POLA violation with \c service=

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index c7a17d7..4ca50b3 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1610,6 +1610,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1623,14 +1625,32 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+	else if (strcmp(user, PQuser(o_conn)) != 0)
+		keep_password = false;
+
 	if (!host)
 		host = PQhost(o_conn);
+	else if (strcmp(host, PQhost(o_conn)) != 0)
+		keep_password = false;
+
 	if (!port)
 		port = PQport(o_conn);
+	else if (strcmp(port, PQport(o_conn)) != 0)
+		keep_password = false;
+
+	has_connection_string = recognized_connection_string(dbname);
+
+	if (has_connection_string)
+		keep_password = false;
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
 
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
@@ -1646,9 +1666,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1656,23 +1680,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index 2001d31..19a5fd4 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,41 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+static const char uri_designator[] = "postgresql://";
+static const char short_uri_designator[] = "postgres://";
+
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * copied from libpq/fe-connect.c
+ */
+static bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 82c926d..e4e4356 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3705,10 +3709,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index bdfb67c..eb6a57b 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 4ac21f2..f290fbc 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1610,6 +1610,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1623,14 +1625,32 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+	else if (strcmp(user, PQuser(o_conn)) != 0)
+		keep_password = false;
+
 	if (!host)
 		host = PQhost(o_conn);
+	else if (strcmp(host, PQhost(o_conn)) != 0)
+		keep_password = false;
+
 	if (!port)
 		port = PQport(o_conn);
+	else if (strcmp(port, PQport(o_conn)) != 0)
+		keep_password = false;
+
+	has_connection_string = recognized_connection_string(dbname);
+
+	if (has_connection_string)
+		keep_password = false;
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
 
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
@@ -1646,9 +1666,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1656,23 +1680,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..c349c66 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,41 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+static const char uri_designator[] = "postgresql://";
+static const char short_uri_designator[] = "postgres://";
+
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * copied from libpq/fe-connect.c
+ */
+static bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index bdfb67c..eb6a57b 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 4ac21f2..f290fbc 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1610,6 +1610,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1623,14 +1625,32 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+	else if (strcmp(user, PQuser(o_conn)) != 0)
+		keep_password = false;
+
 	if (!host)
 		host = PQhost(o_conn);
+	else if (strcmp(host, PQhost(o_conn)) != 0)
+		keep_password = false;
+
 	if (!port)
 		port = PQport(o_conn);
+	else if (strcmp(port, PQport(o_conn)) != 0)
+		keep_password = false;
+
+	has_connection_string = recognized_connection_string(dbname);
+
+	if (has_connection_string)
+		keep_password = false;
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
 
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
@@ -1646,9 +1666,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1656,23 +1680,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 275bdcc..c99a363 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1771,6 +1771,40 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..1da7a46 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,9 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+static const char uri_designator[] = "postgresql://";
+static const char short_uri_designator[] = "postgres://";
+
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index bdfb67c..eb6a57b 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 4ac21f2..bcdf278 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1610,6 +1610,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1623,14 +1625,33 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+	else if (strcmp(user, PQuser(o_conn)) != 0)
+		keep_password = false;
+
 	if (!host)
 		host = PQhost(o_conn);
+	else if (strcmp(host, PQhost(o_conn)) != 0)
+		keep_password = false;
+
 	if (!port)
 		port = PQport(o_conn);
+	else if (strcmp(port, PQport(o_conn)) != 0)
+		keep_password = false;
+
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	if (has_connection_string)
+		keep_password = false;
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
 
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
@@ -1646,9 +1667,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1656,23 +1681,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 275bdcc..e036332 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1771,6 +1771,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..079da43 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index a637001..cae6bf4 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 7c9f28d..ec86e52 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1607,6 +1607,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1620,15 +1622,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1643,9 +1661,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1653,23 +1675,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 275bdcc..e036332 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1771,6 +1771,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..079da43 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index a637001..340a5d5 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -822,6 +824,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 7c9f28d..ec86e52 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1607,6 +1607,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1620,15 +1622,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1643,9 +1661,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1653,23 +1675,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 275bdcc..e036332 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1771,6 +1771,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..079da43 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

commit f0e71c50590b94da5dafb72a377c7c70b49ce488
Author: root <root@localhost.localdomain>
Date:   Fri Feb 20 07:04:53 2015 +0100

    fix segfault due empty variable host

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index a637001..340a5d5 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -822,6 +824,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 7c9f28d..dd9350e 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1607,6 +1607,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1620,15 +1622,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1643,9 +1661,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1653,23 +1675,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
-
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		int paramnum = 0;
+
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 275bdcc..e036332 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1771,6 +1771,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..079da43 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index a637001..173b6c3 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,21 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c       [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string } ] </literal></term>
+        <term><literal>\connect [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -822,6 +825,22 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs, and URIs:
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 4201956..64210bf 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -31,6 +31,7 @@
 #include <sys/stat.h>			/* for stat() */
 #endif
 
+#include "common/connstrings.h"
 #include "portability/instr_time.h"
 
 #include "libpq-fe.h"
@@ -1608,6 +1609,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1621,15 +1624,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = libpq_connstring_is_recognized(dbname);
+
+	keep_password =
+		((strcmp(user, PQuser(o_conn)) == 0) &&
+		 (!host || strcmp(host, PQhost(o_conn)) == 0) &&
+		 (strcmp(port, PQport(o_conn)) == 0) &&
+		 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't trigger
+	 * throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1644,9 +1663,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1654,23 +1677,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
-
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		int			paramnum = 0;
+
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 5ddd654..7f0be95 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -52,6 +52,7 @@
 #include "libpq-fe.h"
 #include "pqexpbuffer.h"
 #include "common.h"
+#include "common/connstrings.h"
 #include "settings.h"
 #include "stringutils.h"
 
@@ -69,6 +70,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3714,10 +3719,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (libpq_connstring_is_recognized(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (libpq_connstring_is_recognized(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
diff --git a/src/common/Makefile b/src/common/Makefile
index 372a21b..d1338c1 100644
--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -26,7 +26,7 @@ LIBS += $(PTHREAD_LIBS)
 OBJS_COMMON = exec.o pg_crc.o pg_lzcompress.o pgfnames.o psprintf.o relpath.o \
 	rmtree.o string.o username.o wait_error.o
 
-OBJS_FRONTEND = $(OBJS_COMMON) fe_memutils.o
+OBJS_FRONTEND = $(OBJS_COMMON) fe_memutils.o connstrings.o
 
 OBJS_SRV = $(OBJS_COMMON:%.o=%_srv.o)
 
diff --git a/src/common/connstrings.c b/src/common/connstrings.c
new file mode 100644
index 0000000..aa5fdb0
--- /dev/null
+++ b/src/common/connstrings.c
@@ -0,0 +1,51 @@
+/*
+ * connstrings.c
+ *		connecting string related functions
+ *
+ *	Copyright (c) 2012-2015, PostgreSQL Global Development Group
+ *
+ *	src/include/common/connstrings.c
+ */
+#include "postgres_fe.h"
+
+#include <string.h>
+
+#include "common/connstrings.h"
+
+
+/* The connection URI must start with either of the following designators: */
+static const char uri_designator[] = "postgresql://";
+static const char short_uri_designator[] = "postgres://";
+
+/*
+ * Checks if the given connection string starts with either of the valid URI
+ * prefix designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ */
+int
+libpq_connstring_uri_prefix_length(const char *connstr)
+{
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * Must be consistent with libpq's parse_connection_string: anything for which
+ * this returns true should at least look like it's parseable by that routine.
+ */
+bool
+libpq_connstring_is_recognized(const char *connstr)
+{
+	return libpq_connstring_uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
diff --git a/src/include/common/connstrings.h b/src/include/common/connstrings.h
new file mode 100644
index 0000000..1fe624e
--- /dev/null
+++ b/src/include/common/connstrings.h
@@ -0,0 +1,16 @@
+/*
+ *	connstrings.h
+ *		connecting string related prototypes
+ *
+ *	Copyright (c) 2012-2015, PostgreSQL Global Development Group
+ *
+ *	src/include/common/connstrings.h
+ */
+#ifndef CONNSTRINGS_H
+#define CONNSTRINGS_H
+
+
+extern int	libpq_connstring_uri_prefix_length(const char *connstr);
+extern bool	libpq_connstring_is_recognized(const char *connstr);
+
+#endif		/* CONNSTRINGS_H */
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 25961b1..e5407dd 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -22,6 +22,7 @@
 #include <time.h>
 #include <unistd.h>
 
+#include "common/connstrings.h"
 #include "libpq-fe.h"
 #include "libpq-int.h"
 #include "fe-auth.h"
@@ -339,8 +340,6 @@ static void closePGconn(PGconn *conn);
 static PQconninfoOption *conninfo_init(PQExpBuffer errorMessage);
 static PQconninfoOption *parse_connection_string(const char *conninfo,
 						PQExpBuffer errorMessage, bool use_defaults);
-static int	uri_prefix_length(const char *connstr);
-static bool recognized_connection_string(const char *connstr);
 static PQconninfoOption *conninfo_parse(const char *conninfo,
 			   PQExpBuffer errorMessage, bool use_defaults);
 static PQconninfoOption *conninfo_array_parse(const char *const * keywords,
@@ -971,7 +970,7 @@ PQsetdbLogin(const char *pghost, const char *pgport, const char *pgoptions,
 	 * If the dbName parameter contains what looks like a connection string,
 	 * parse it into conn struct using connectOptions1.
 	 */
-	if (dbName && recognized_connection_string(dbName))
+	if (dbName && libpq_connstring_is_recognized(dbName))
 	{
 		if (!connectOptions1(conn, dbName))
 			return conn;
@@ -4179,13 +4178,15 @@ conninfo_init(PQExpBuffer errorMessage)
  *
  * If use_defaults is TRUE, default values are filled in (from a service file,
  * environment variables, etc).
+ *
+ * Make sure to keep libpq_connstring_is_recognized in sync with this.
  */
 static PQconninfoOption *
 parse_connection_string(const char *connstr, PQExpBuffer errorMessage,
 						bool use_defaults)
 {
 	/* Parse as URI if connection string matches URI prefix */
-	if (uri_prefix_length(connstr) != 0)
+	if (libpq_connstring_uri_prefix_length(connstr) != 0)
 		return conninfo_uri_parse(connstr, errorMessage, use_defaults);
 
 	/* Parse as default otherwise */
@@ -4193,39 +4194,6 @@ parse_connection_string(const char *connstr, PQExpBuffer errorMessage,
 }
 
 /*
- * Checks if connection string starts with either of the valid URI prefix
- * designators.
- *
- * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
- */
-static int
-uri_prefix_length(const char *connstr)
-{
-	if (strncmp(connstr, uri_designator,
-				sizeof(uri_designator) - 1) == 0)
-		return sizeof(uri_designator) - 1;
-
-	if (strncmp(connstr, short_uri_designator,
-				sizeof(short_uri_designator) - 1) == 0)
-		return sizeof(short_uri_designator) - 1;
-
-	return 0;
-}
-
-/*
- * Recognized connection string either starts with a valid URI prefix or
- * contains a "=" in it.
- *
- * Must be consistent with parse_connection_string: anything for which this
- * returns true should at least look like it's parseable by that routine.
- */
-static bool
-recognized_connection_string(const char *connstr)
-{
-	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
-}
-
-/*
  * Subroutine for parse_connection_string
  *
  * Deal with a string containing key=value pairs.
@@ -4400,7 +4368,7 @@ conninfo_parse(const char *conninfo, PQExpBuffer errorMessage,
  *
  * If expand_dbname is non-zero, and the value passed for the first occurrence
  * of "dbname" keyword is a connection string (as indicated by
- * recognized_connection_string) then parse and process it, overriding any
+ * libpq_connstring_is_recognized) then parse and process it, overriding any
  * previously processed conflicting keywords. Subsequent keywords will take
  * precedence, however.
  */
@@ -4431,7 +4399,7 @@ conninfo_array_parse(const char *const * keywords, const char *const * values,
 			 * defaults here -- those get picked up later. We only want to
 			 * override for those parameters actually passed.
 			 */
-			if (recognized_connection_string(pvalue))
+			if (libpq_connstring_is_recognized(pvalue))
 			{
 				dbname_options = parse_connection_string(pvalue, errorMessage, false);
 				if (dbname_options == NULL)
@@ -4722,7 +4690,7 @@ conninfo_uri_parse_options(PQconninfoOption *options, const char *uri,
 	start = buf;
 
 	/* Skip the URI prefix */
-	prefix_len = uri_prefix_length(uri);
+	prefix_len = libpq_connstring_uri_prefix_length(uri);
 	if (prefix_len == 0)
 	{
 		/* Should never happen */

>From 830d41b9d23716af29491cbab59808c35e25ec12 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 20 Feb 2015 14:36:41 -0300
Subject: [PATCH] Fix psql's \c to work with URIs and conninfo strings
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This makes it more consistent with what can be given in the command
line.

Authors: Andrew Dunstan, David Fetter, Andrew Gierth, Pavel Stěhule
---
 doc/src/sgml/ref/psql-ref.sgml    | 30 ++++++++++++++---
 src/bin/psql/command.c            | 69 +++++++++++++++++++++++++++------------
 src/bin/psql/tab-complete.c       | 20 ++++++++++--
 src/common/Makefile               |  2 +-
 src/common/connstrings.c          | 52 +++++++++++++++++++++++++++++
 src/include/common/connstrings.h  | 16 +++++++++
 src/interfaces/libpq/fe-connect.c | 36 +-------------------
 7 files changed, 162 insertions(+), 63 deletions(-)
 create mode 100644 src/common/connstrings.c
 create mode 100644 src/include/common/connstrings.h

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index a637001..a218af8 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,23 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c       [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string } ] </literal></term>
+        <term><literal>\connect [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>.
+        If the new connection is successfully made, the
+        previous connection is closed.
+        When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.
+        If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -822,6 +827,23 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING">
+        takes two forms: keyword-value pairs, and URIs:
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 7c9f28d..7d8d5bb 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1607,6 +1607,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1620,15 +1622,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password =
+		((strcmp(user, PQuser(o_conn)) == 0) &&
+		 (!host || strcmp(host, PQhost(o_conn)) == 0) &&
+		 (strcmp(port, PQport(o_conn)) == 0) &&
+		 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't trigger
+	 * throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1643,9 +1661,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1653,23 +1675,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
-
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		int			paramnum = 0;
+
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
diff --git a/src/common/Makefile b/src/common/Makefile
index 372a21b..d1338c1 100644
--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -26,7 +26,7 @@ LIBS += $(PTHREAD_LIBS)
 OBJS_COMMON = exec.o pg_crc.o pg_lzcompress.o pgfnames.o psprintf.o relpath.o \
 	rmtree.o string.o username.o wait_error.o
 
-OBJS_FRONTEND = $(OBJS_COMMON) fe_memutils.o
+OBJS_FRONTEND = $(OBJS_COMMON) fe_memutils.o connstrings.o
 
 OBJS_SRV = $(OBJS_COMMON:%.o=%_srv.o)
 
diff --git a/src/common/connstrings.c b/src/common/connstrings.c
new file mode 100644
index 0000000..4a49179
--- /dev/null
+++ b/src/common/connstrings.c
@@ -0,0 +1,52 @@
+/*
+ * connstrings.c
+ *		connecting string processing functions
+ *
+ *	Copyright (c) 2012-2015, PostgreSQL Global Development Group
+ *
+ *	src/include/common/connstrings.c
+ */
+#include "postgres_fe.h"
+
+#include <string.h>
+
+#include "common/connstrings.h"
+
+
+/* The connection URI must start with either of the following designators: */
+static const char uri_designator[] = "postgresql://";
+static const char short_uri_designator[] = "postgres://";
+
+
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ */
+int
+uri_prefix_length(const char *connstr)
+{
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * Must be consistent with parse_connection_string: anything for which this
+ * returns true should at least look like it's parseable by that routine.
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
diff --git a/src/include/common/connstrings.h b/src/include/common/connstrings.h
new file mode 100644
index 0000000..5644bbe
--- /dev/null
+++ b/src/include/common/connstrings.h
@@ -0,0 +1,16 @@
+/*
+ *	connstrings.h
+ *		connecting string processing prototypes
+ *
+ *	Copyright (c) 2012-2015, PostgreSQL Global Development Group
+ *
+ *	src/include/common/connstrings.h
+ */
+#ifndef CONNSTRINGS_H
+#define CONNSTRINGS_H
+
+
+extern int	uri_prefix_length(const char *connstr);
+extern bool	recognized_connection_string(const char *connstr);
+
+#endif		/* CONNSTRINGS_H */
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index e2a06b3..cc14e4e 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -22,6 +22,7 @@
 #include <time.h>
 #include <unistd.h>
 
+#include "common/connstrings.h"
 #include "libpq-fe.h"
 #include "libpq-int.h"
 #include "fe-auth.h"
@@ -339,8 +340,6 @@ static void closePGconn(PGconn *conn);
 static PQconninfoOption *conninfo_init(PQExpBuffer errorMessage);
 static PQconninfoOption *parse_connection_string(const char *conninfo,
 						PQExpBuffer errorMessage, bool use_defaults);
-static int	uri_prefix_length(const char *connstr);
-static bool recognized_connection_string(const char *connstr);
 static PQconninfoOption *conninfo_parse(const char *conninfo,
 			   PQExpBuffer errorMessage, bool use_defaults);
 static PQconninfoOption *conninfo_array_parse(const char *const * keywords,
@@ -4193,39 +4192,6 @@ parse_connection_string(const char *connstr, PQExpBuffer errorMessage,
 }
 
 /*
- * Checks if connection string starts with either of the valid URI prefix
- * designators.
- *
- * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
- */
-static int
-uri_prefix_length(const char *connstr)
-{
-	if (strncmp(connstr, uri_designator,
-				sizeof(uri_designator) - 1) == 0)
-		return sizeof(uri_designator) - 1;
-
-	if (strncmp(connstr, short_uri_designator,
-				sizeof(short_uri_designator) - 1) == 0)
-		return sizeof(short_uri_designator) - 1;
-
-	return 0;
-}
-
-/*
- * Recognized connection string either starts with a valid URI prefix or
- * contains a "=" in it.
- *
- * Must be consistent with parse_connection_string: anything for which this
- * returns true should at least look like it's parseable by that routine.
- */
-static bool
-recognized_connection_string(const char *connstr)
-{
-	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
-}
-
-/*
  * Subroutine for parse_connection_string
  *
  * Deal with a string containing key=value pairs.
-- 
2.1.4

>From 1fcca51973cdd91b1620fdf6502f658f6b557c16 Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Wed, 25 Feb 2015 13:51:17 -0800
Subject: [PATCH] From Alvaro Herrera

---
 doc/src/sgml/ref/psql-ref.sgml | 31 ++++++++++++++++---
 src/bin/psql/command.c         | 67 +++++++++++++++++++++++++++++-------------
 src/bin/psql/common.c          | 36 +++++++++++++++++++++++
 src/bin/psql/common.h          |  2 ++
 src/bin/psql/tab-complete.c    | 20 +++++++++++--
 5 files changed, 130 insertions(+), 26 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index a637001..340a5d5 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -796,18 +796,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -822,6 +824,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 7c9f28d..dd9350e 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1607,6 +1607,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1620,15 +1622,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1643,9 +1661,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1653,23 +1675,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 275bdcc..e036332 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1771,6 +1771,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index eb14d1c..079da43 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -49,4 +49,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index e39a07c..1c57924 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3706,10 +3710,22 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST_CS(my_list);
 	}
+
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 	else if (strcmp(prev2_wd, "\\connect") == 0 || strcmp(prev2_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	{
+		if (recognized_connection_string(prev_wd))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_roles);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
-- 
2.1.0

>From 64c7d3bcfad80dc80857b2ea06c9f2b7fff8f2a5 Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Wed, 25 Feb 2015 13:51:17 -0800
Subject: [PATCH] From Alvaro Herrera

Resolved conflicts:
	src/bin/psql/tab-complete.c

Resolved conflicts:
	src/bin/psql/command.c

Resolved conflicts:
	doc/src/sgml/ref/psql-ref.sgml
	src/bin/psql/command.c
---
 doc/src/sgml/ref/psql-ref.sgml | 61 ++++++++++++++++++++++-----------
 src/bin/psql/command.c         | 77 ++++++++++++++++++++++++++++++++----------
 src/bin/psql/common.c          | 36 ++++++++++++++++++++
 src/bin/psql/common.h          |  2 ++
 src/bin/psql/tab-complete.c    | 12 ++++++-
 5 files changed, 150 insertions(+), 38 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 15bbd7a..b7f0601 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -751,33 +751,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\C [ <replaceable class="parameter">title</replaceable> ]</literal></term>
-        <listitem>
-        <para>
-        Sets the title of any tables being printed as the result of a
-        query or unset any such title. This command is equivalent to
-        <literal>\pset title <replaceable
-        class="parameter">title</replaceable></literal>. (The name of
-        this command derives from <quote>caption</quote>, as it was
-        previously only used to set the caption in an
-        <acronym>HTML</acronym> table.)
-        </para>
-        </listitem>
-      </varlistentry>
-
-      <varlistentry>
-        <term><literal>\connect</literal> (or <literal>\c</literal>) <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -792,6 +779,42 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><literal>\C [ <replaceable class="parameter">title</replaceable> ]</literal></term>
+        <listitem>
+        <para>
+        Sets the title of any tables being printed as the result of a
+        query or unset any such title. This command is equivalent to
+        <literal>\pset title <replaceable
+        class="parameter">title</replaceable></literal>. (The name of
+        this command derives from <quote>caption</quote>, as it was
+        previously only used to set the caption in an
+        <acronym>HTML</acronym> table.)
+        </para>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index d2967ed..49c20bd 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1240,16 +1240,46 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
+
+	if (!o_conn && (!dbname || !user || !host || !port))
+	{
+		/*
+		 * We don't know the supplied connection parameters and don't want to
+		 * connect to the wrong database by using defaults, so require all
+		 * parameters to be specified.
+		 */
+		psql_error("All connection parameters must be supplied because no "
+				   "database connection exists\n");
+		return false;
+	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1264,9 +1294,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1274,21 +1308,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	7
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = NULL;
-		values[6] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 5013ad3..6938d08 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1514,6 +1514,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index 838a552..155771c 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -63,4 +63,6 @@ extern const char *session_username(void);
 
 extern char *expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index feeb76f..98e23b9 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -2451,7 +2455,13 @@ psql_completion(char *text, int start, int end)
 /* Backslash commands */
 /* TODO:  \dc \dd \dl */
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
-- 
2.1.0

>From 968ca9febefe48b2424049a21a9cf51b331defcd Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Wed, 25 Feb 2015 13:51:17 -0800
Subject: [PATCH] From Alvaro Herrera

Resolved conflicts:
	src/bin/psql/tab-complete.c

Resolved conflicts:
	src/bin/psql/command.c
---
 doc/src/sgml/ref/psql-ref.sgml | 31 ++++++++++++++---
 src/bin/psql/command.c         | 79 +++++++++++++++++++++++++++++++-----------
 src/bin/psql/common.c          | 36 +++++++++++++++++++
 src/bin/psql/common.h          |  2 ++
 src/bin/psql/tab-complete.c    | 12 ++++++-
 5 files changed, 135 insertions(+), 25 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 6b64cd5..54bde8d 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -745,18 +745,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -771,6 +773,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index fdb2404..adfc60f 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1467,16 +1467,46 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
+
+	if (!o_conn && (!dbname || !user || !host || !port))
+	{
+		/*
+		 * We don't know the supplied connection parameters and don't want to
+		 * connect to the wrong database by using defaults, so require all
+		 * parameters to be specified.
+		 */
+		psql_error("All connection parameters must be supplied because no "
+				   "database connection exists\n");
+		return false;
+	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1491,9 +1521,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1501,23 +1535,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index abb1082..82f2320 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1514,6 +1514,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index a26b868..20951d7 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -63,4 +63,6 @@ extern const char *session_username(void);
 
 extern char *expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d90d281..b5316fa 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -2776,7 +2780,13 @@ psql_completion(char *text, int start, int end)
 /* Backslash commands */
 /* TODO:  \dc \dd \dl */
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
-- 
2.1.0

>From 8c21e0d49c0ce8c4b21bd14d13b681f9148d68da Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Wed, 25 Feb 2015 13:51:17 -0800
Subject: [PATCH] From Alvaro Herrera

Resolved conflicts:
	src/bin/psql/tab-complete.c

Resolved conflicts:
	src/bin/psql/command.c
---
 doc/src/sgml/ref/psql-ref.sgml | 31 ++++++++++++++---
 src/bin/psql/command.c         | 79 +++++++++++++++++++++++++++++++-----------
 src/bin/psql/common.c          | 36 +++++++++++++++++++
 src/bin/psql/common.h          |  2 ++
 src/bin/psql/tab-complete.c    | 12 ++++++-
 5 files changed, 135 insertions(+), 25 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 9d9c573..7d741ed 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -771,18 +771,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -797,6 +799,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index b74db20..5a8b24d 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1506,16 +1506,46 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
+
+	if (!o_conn && (!dbname || !user || !host || !port))
+	{
+		/*
+		 * We don't know the supplied connection parameters and don't want to
+		 * connect to the wrong database by using defaults, so require all
+		 * parameters to be specified.
+		 */
+		psql_error("All connection parameters must be supplied because no "
+				   "database connection exists\n");
+		return false;
+	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1530,9 +1560,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1540,23 +1574,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 49ee47a..8b13a8f 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1626,6 +1626,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index cfe0dad..7364908 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -63,4 +63,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 870dd6f..ae55189 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -2938,7 +2942,13 @@ psql_completion(char *text, int start, int end)
 /* Backslash commands */
 /* TODO:  \dc \dd \dl */
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
-- 
2.1.0

>From 2ab01b469297e0dd0eeae8b227924667e9aad814 Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Wed, 25 Feb 2015 13:51:17 -0800
Subject: [PATCH] From Alvaro Herrera

Resolved conflicts:
	src/bin/psql/tab-complete.c
---
 doc/src/sgml/ref/psql-ref.sgml | 31 ++++++++++++++++---
 src/bin/psql/command.c         | 67 +++++++++++++++++++++++++++++-------------
 src/bin/psql/common.c          | 36 +++++++++++++++++++++++
 src/bin/psql/common.h          |  2 ++
 src/bin/psql/tab-complete.c    | 12 +++++++-
 5 files changed, 123 insertions(+), 25 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index ca1daea..a8403cb 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -772,18 +772,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -798,6 +800,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 0152a76..8786a1a 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1559,6 +1559,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1572,15 +1574,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1595,9 +1613,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1605,23 +1627,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 6f16a5c..2d98d44 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1654,6 +1654,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index db645da..dd2fdcf 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -46,4 +46,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 0a210cb..a4e5a6e 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3256,7 +3260,13 @@ psql_completion(char *text, int start, int end)
 /* Backslash commands */
 /* TODO:  \dc \dd \dl */
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
-- 
2.1.0

>From 86f7d6549dc74c1baa58cf9d66f2f2cf4df32666 Mon Sep 17 00:00:00 2001
From: David Fetter <david@fetter.org>
Date: Wed, 25 Feb 2015 13:51:17 -0800
Subject: [PATCH] From Alvaro Herrera

Resolved conflicts:
	src/bin/psql/tab-complete.c
---
 doc/src/sgml/ref/psql-ref.sgml | 31 ++++++++++++++++---
 src/bin/psql/command.c         | 67 +++++++++++++++++++++++++++++-------------
 src/bin/psql/common.c          | 36 +++++++++++++++++++++++
 src/bin/psql/common.h          |  2 ++
 src/bin/psql/tab-complete.c    | 12 +++++++-
 5 files changed, 123 insertions(+), 25 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 1d034df..d985201 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -778,18 +778,20 @@ testdb=&gt;
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal> [ { [ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> string | <replaceable class="parameter">URI</replaceable> } ] </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
+        server using positional parameters as described below, a
+        <parameter>conninfo</parameter> string, or a <acronym>URI</acronym>. If the new connection is
+        successfully made, the
+        previous connection is closed.  When using positional parameters, if any of <replaceable
         class="parameter">dbname</replaceable>, <replaceable
         class="parameter">username</replaceable>, <replaceable
         class="parameter">host</replaceable> or <replaceable
         class="parameter">port</replaceable> are omitted or specified
         as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
+        previous connection is used.  If using positional parameters and there is no previous
         connection, the <application>libpq</application> default for
         the parameter's value is used.
         </para>
@@ -804,6 +806,27 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Positional syntax:
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+</programlisting>
+        </para>
+
+        <para>
+        The conninfo form detailed in <xref linkend="LIBPQ-CONNSTRING"> takes two forms: keyword-value pairs
+        </para>
+<programlisting>
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+</programlisting>
+        <para>
+        and URIs:
+        </para>
+<programlisting>
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 8f8c785..391f60b 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1595,6 +1595,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password = true;
+	bool		has_connection_string = false;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1608,15 +1610,31 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
 	if (!user)
 		user = PQuser(o_conn);
+
 	if (!host)
 		host = PQhost(o_conn);
+
 	if (!port)
 		port = PQport(o_conn);
 
+	if (dbname)
+		has_connection_string = recognized_connection_string(dbname);
+
+	keep_password = (
+			(strcmp(user, PQuser(o_conn)) == 0) &&
+			(!host || strcmp(host, PQhost(o_conn)) == 0) &&
+			(strcmp(port, PQport(o_conn)) == 0) &&
+			 !has_connection_string);
+
+	/*
+	 * Unlike the previous stanzas, changing only the dbname shouldn't
+	 * trigger throwing away the password.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1631,9 +1649,13 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
@@ -1641,23 +1663,28 @@ do_connect(char *dbname, char *user, char *host, char *port)
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int paramnum = 0;
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index c08c813..da4f414 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -1691,6 +1691,42 @@ session_username(void)
 		return PQuser(pset.db);
 }
 
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	const char uri_designator[] = "postgresql://";
+	const char short_uri_designator[] = "postgres://";
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * XXX copied from libpq/fe-connect.c
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}
+
 
 /* expand_tilde
  *
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index f58c545..069c1b8 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -46,4 +46,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 9841c1a..3e51ecb 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -69,6 +69,10 @@ extern char *filename_completion_function();
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "
 
+/* XXX Until we can tab complete for URIs and services, each of which
+ * should populate their own lists */
+static const char *const empty_list[] = {NULL};
+
 /*
  * This struct is used to define "schema queries", which are custom-built
  * to obtain possibly-schema-qualified names of database objects.  There is
@@ -3413,7 +3417,13 @@ psql_completion(const char *text, int start, int end)
 /* Backslash commands */
 /* TODO:  \dc \dd \dl */
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		/* URI/service completion.  Nothing for now */
+		if (recognized_connection_string(text))
+			COMPLETE_WITH_LIST(empty_list);
+		else
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);
-- 
2.1.0