pg_collation_actual_version() ERROR: cache lookup failed for collation 123

From 992608eb81265856af3b9cbcb63597d91876090a Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:10:40 +1300
Subject: [PATCH 1/4] Improve error message for pg_collation_actual_version().

Instead of an internal "cache lookup failed" message, show a message
intended for end user consumption, considering this is a user-exposed
function.

Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/backend/catalog/index.c          |  5 +++--
 src/backend/catalog/pg_depend.c      |  3 ++-
 src/backend/commands/collationcmds.c |  8 +++++++-
 src/backend/utils/adt/pg_locale.c    | 17 +++++++++++++++--
 src/include/utils/pg_locale.h        |  2 +-
 5 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 1514937748..1c808f55c5 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1290,7 +1290,8 @@ do_collation_version_check(const ObjectAddress *otherObject,
 		return false;
 
 	/* Ask the provider for the current version.  Give up if unsupported. */
-	current_version = get_collation_version_for_oid(otherObject->objectId);
+	current_version = get_collation_version_for_oid(otherObject->objectId,
+													NULL);
 	if (!current_version)
 		return false;
 
@@ -1369,7 +1370,7 @@ do_collation_version_update(const ObjectAddress *otherObject,
 	if (OidIsValid(*coll) && otherObject->objectId != *coll)
 		return false;
 
-	*new_version = get_collation_version_for_oid(otherObject->objectId);
+	*new_version = get_collation_version_for_oid(otherObject->objectId, NULL);
 
 	return true;
 }
diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
index 63da24322d..aee59eef39 100644
--- a/src/backend/catalog/pg_depend.c
+++ b/src/backend/catalog/pg_depend.c
@@ -116,7 +116,8 @@ recordMultipleDependencies(const ObjectAddress *depender,
 					referenced->objectId == POSIX_COLLATION_OID)
 					continue;
 
-				version = get_collation_version_for_oid(referenced->objectId);
+				version = get_collation_version_for_oid(referenced->objectId,
+														NULL);
 
 				/*
 				 * Default collation is pinned, so we need to force recording
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 9634ae6809..b3c59e6e9f 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -272,8 +272,14 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
+	bool		found;
 
-	version = get_collation_version_for_oid(collid);
+	version = get_collation_version_for_oid(collid, &found);
+
+	if (!found)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("no collation found for OID %u", collid)));
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index e9c1231f9b..3cd9257800 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1726,10 +1726,12 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 /*
  * Get provider-specific collation version string for a given collation OID.
  * Return NULL if the provider doesn't support versions, or the collation is
- * unversioned (for example "C").
+ * unversioned (for example "C").  If "found" is non-NULL, unknown OIDs are
+ * reported through this output parameter; otherwise, an internal error is
+ * raised for unknown OIDs.
  */
 char *
-get_collation_version_for_oid(Oid oid)
+get_collation_version_for_oid(Oid oid, bool *found)
 {
 	HeapTuple	tp;
 	char	   *version;
@@ -1744,6 +1746,8 @@ get_collation_version_for_oid(Oid oid)
 		dbform = (Form_pg_database) GETSTRUCT(tp);
 		version = get_collation_actual_version(COLLPROVIDER_LIBC,
 											   NameStr(dbform->datcollate));
+		if (found)
+			*found = true;
 	}
 	else
 	{
@@ -1751,10 +1755,19 @@ get_collation_version_for_oid(Oid oid)
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(oid));
 		if (!HeapTupleIsValid(tp))
+		{
+			if (found)
+			{
+				*found = false;
+				return NULL;
+			}
 			elog(ERROR, "cache lookup failed for collation %u", oid);
+		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 		version = get_collation_actual_version(collform->collprovider,
 											   NameStr(collform->collcollate));
+		if (found)
+			*found = true;
 	}
 
 	ReleaseSysCache(tp);
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 34dff74bd1..9d73774a19 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -103,7 +103,7 @@ typedef struct pg_locale_struct *pg_locale_t;
 
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
-extern char *get_collation_version_for_oid(Oid collid);
+extern char *get_collation_version_for_oid(Oid collid, bool *found);
 
 #ifdef USE_ICU
 extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);
-- 
2.30.0

From 190263b628cd48f5058f983c4ef33389a09afae8 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:19:40 +1300
Subject: [PATCH 2/4] pg_collation_actual_version() ->
 pg_collation_current_version().

The new name seems a bit more natural.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 doc/src/sgml/func.sgml                         |  8 ++++----
 src/backend/commands/collationcmds.c           |  2 +-
 src/backend/utils/adt/pg_locale.c              | 14 +++++++-------
 src/include/catalog/pg_proc.dat                |  4 ++--
 src/test/regress/expected/collate.icu.utf8.out |  2 +-
 src/test/regress/sql/collate.icu.utf8.sql      |  2 +-
 6 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1ab31a9056..d8224272a5 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -26227,14 +26227,14 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
-         <primary>pg_collation_actual_version</primary>
+         <primary>pg_collation_current_version</primary>
         </indexterm>
-        <function>pg_collation_actual_version</function> ( <type>oid</type> )
+        <function>pg_collation_current_version</function> ( <type>oid</type> )
         <returnvalue>text</returnvalue>
        </para>
        <para>
-        Returns the actual version of the collation object as it is currently
-        installed in the operating system.  <literal>null</literal> is returned
+        Returns the version of the collation object as reported by the ICU
+        library or operating system.  <literal>null</literal> is returned
         on operating systems where <productname>PostgreSQL</productname>
         doesn't have support for versions.
        </para></entry>
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index b3c59e6e9f..a694e19dd1 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -268,7 +268,7 @@ IsThereCollationInNamespace(const char *collname, Oid nspOid)
 }
 
 Datum
-pg_collation_actual_version(PG_FUNCTION_ARGS)
+pg_collation_current_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 3cd9257800..1d8af6fb88 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -127,8 +127,8 @@ static char *IsoLocaleName(const char *);	/* MSVC specific */
 static void icu_set_collation_attributes(UCollator *collator, const char *loc);
 #endif
 
-static char *get_collation_actual_version(char collprovider,
-										  const char *collcollate);
+static char *get_collation_current_version(char collprovider,
+										   const char *collcollate);
 
 /*
  * pg_perm_setlocale
@@ -1610,7 +1610,7 @@ pg_newlocale_from_collation(Oid collid)
  * the operating system/library.
  */
 static char *
-get_collation_actual_version(char collprovider, const char *collcollate)
+get_collation_current_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
@@ -1744,8 +1744,8 @@ get_collation_version_for_oid(Oid oid, bool *found)
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
 		dbform = (Form_pg_database) GETSTRUCT(tp);
-		version = get_collation_actual_version(COLLPROVIDER_LIBC,
-											   NameStr(dbform->datcollate));
+		version = get_collation_current_version(COLLPROVIDER_LIBC,
+												NameStr(dbform->datcollate));
 		if (found)
 			*found = true;
 	}
@@ -1764,8 +1764,8 @@ get_collation_version_for_oid(Oid oid, bool *found)
 			elog(ERROR, "cache lookup failed for collation %u", oid);
 		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
-		version = get_collation_actual_version(collform->collprovider,
-											   NameStr(collform->collcollate));
+		version = get_collation_current_version(collform->collprovider,
+												NameStr(collform->collcollate));
 		if (found)
 			*found = true;
 	}
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 1487710d59..16044125ba 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -11321,9 +11321,9 @@
 
 { oid => '3448',
   descr => 'get actual version of collation from operating system',
-  proname => 'pg_collation_actual_version', procost => '100',
+  proname => 'pg_collation_current_version', procost => '100',
   provolatile => 'v', prorettype => 'text', proargtypes => 'oid',
-  prosrc => 'pg_collation_actual_version' },
+  prosrc => 'pg_collation_current_version' },
 
 # system management/monitoring related functions
 { oid => '3353', descr => 'list files in the log directory',
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index bc3752e923..970638ed37 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -2018,7 +2018,7 @@ SELECT objid::regclass::text collate "C", refobjid::regcollation::text collate "
 CASE
 WHEN refobjid = 'default'::regcollation THEN 'XXX' -- depends on libc version support
 WHEN refobjversion IS NULL THEN 'version not tracked'
-WHEN refobjversion = pg_collation_actual_version(refobjid) THEN 'up to date'
+WHEN refobjversion = pg_collation_current_version(refobjid) THEN 'up to date'
 ELSE 'out of date'
 END AS version
 FROM pg_depend d
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 0de2ed8d85..be5b464ffa 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -820,7 +820,7 @@ SELECT objid::regclass::text collate "C", refobjid::regcollation::text collate "
 CASE
 WHEN refobjid = 'default'::regcollation THEN 'XXX' -- depends on libc version support
 WHEN refobjversion IS NULL THEN 'version not tracked'
-WHEN refobjversion = pg_collation_actual_version(refobjid) THEN 'up to date'
+WHEN refobjversion = pg_collation_current_version(refobjid) THEN 'up to date'
 ELSE 'out of date'
 END AS version
 FROM pg_depend d
-- 
2.30.0

From 4885e32e5e978631b1232feee4c2078a589a35cd Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:36:43 +1300
Subject: [PATCH 3/4] Refactor get_collation_current_version().

The code paths for three different OSes finished up with three different
ways of excluding C[.xxx] and POSIX from consideration.  Merge them.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/backend/utils/adt/pg_locale.c | 35 +++++--------------------------
 1 file changed, 5 insertions(+), 30 deletions(-)

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 1d8af6fb88..7d2d1a9a04 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1636,37 +1636,18 @@ get_collation_current_version(char collprovider, const char *collcollate)
 	}
 	else
 #endif
-	if (collprovider == COLLPROVIDER_LIBC)
+	if (collprovider == COLLPROVIDER_LIBC &&
+		pg_strcasecmp("C", collcollate) != 0 &&
+		pg_strncasecmp("C.", collcollate, 2) != 0 &&
+		pg_strcasecmp("POSIX", collcollate) != 0 &&
+		pg_strncasecmp("POSIX.", collcollate, 5) != 0)
 	{
 #if defined(__GLIBC__)
-		char	   *copy = pstrdup(collcollate);
-		char	   *copy_suffix = strstr(copy, ".");
-		bool		need_version = true;
-
-		/*
-		 * Check for names like C.UTF-8 by chopping off the encoding suffix on
-		 * our temporary copy, so we can skip the version.
-		 */
-		if (copy_suffix)
-			*copy_suffix = '\0';
-		if (pg_strcasecmp("c", copy) == 0 ||
-			pg_strcasecmp("posix", copy) == 0)
-			need_version = false;
-		pfree(copy);
-		if (!need_version)
-			return NULL;
-
 		/* Use the glibc version because we don't have anything better. */
 		collversion = pstrdup(gnu_get_libc_version());
 #elif defined(LC_VERSION_MASK)
 		locale_t    loc;
 
-		/* C[.encoding] and POSIX never change. */
-		if (strcmp("C", collcollate) == 0 ||
-			strncmp("C.", collcollate, 2) == 0 ||
-			strcmp("POSIX", collcollate) == 0)
-			return NULL;
-
 		/* Look up FreeBSD collation version. */
 		loc = newlocale(LC_COLLATE, collcollate, NULL);
 		if (loc)
@@ -1687,12 +1668,6 @@ get_collation_current_version(char collprovider, const char *collcollate)
 		NLSVERSIONINFOEX version = {sizeof(NLSVERSIONINFOEX)};
 		WCHAR		wide_collcollate[LOCALE_NAME_MAX_LENGTH];
 
-		/* These would be invalid arguments, but have no version. */
-		if (pg_strcasecmp("c", collcollate) == 0 ||
-			pg_strcasecmp("posix", collcollate) == 0)
-			return NULL;
-
-		/* For all other names, ask the OS. */
 		MultiByteToWideChar(CP_ACP, 0, collcollate, -1, wide_collcollate,
 							LOCALE_NAME_MAX_LENGTH);
 		if (!GetNLSVersionEx(COMPARE_STRING, wide_collcollate, &version))
-- 
2.30.0

From eb83951dbe44940e8e8239dac214cbab9d3e0e9e Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 15:05:04 +1300
Subject: [PATCH 4/4] Tab-complete CREATE COLLATION.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/bin/psql/tab-complete.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 1e1c315bae..da45877ed4 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2424,6 +2424,20 @@ psql_completion(const char *text, int start, int end)
 	else if (Matches("CREATE", "ACCESS", "METHOD", MatchAny, "TYPE", MatchAny))
 		COMPLETE_WITH("HANDLER");
 
+	/* CREATE COLLATION */
+	else if (Matches("CREATE", "COLLATION", MatchAny))
+		COMPLETE_WITH("(");
+	else if (HeadMatches("CREATE", "COLLATION"))
+	{
+		if (TailMatches("(|*,"))
+			COMPLETE_WITH("LOCALE =", "LC_COLLATE =", "LC_CTYPE =",
+						  "PROVIDER =", "DETERMINISTIC =");
+		else if (TailMatches("PROVIDER", "="))
+			COMPLETE_WITH("libc", "icu");
+		else if (TailMatches("DETERMINISTIC", "="))
+			COMPLETE_WITH("true", "false");
+	}
+
 	/* CREATE DATABASE */
 	else if (Matches("CREATE", "DATABASE", MatchAny))
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
-- 
2.30.0

From 36acff2cdb3dbde81b82ca425b61b0b8a62e27c9 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:10:40 +1300
Subject: [PATCH v2 1/4] Hide internal error for
 pg_collation_actual_version(<bad OID>).

Instead of an unsightly internal "cache lookup failed" message, just
return NULL for bad OIDs, as seems to be the convention for other
similar things.

Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/backend/catalog/index.c          | 5 +++--
 src/backend/catalog/pg_depend.c      | 3 ++-
 src/backend/commands/collationcmds.c | 2 +-
 src/backend/utils/adt/pg_locale.c    | 9 +++++++--
 src/include/utils/pg_locale.h        | 2 +-
 5 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index b4ab0b88ad..a9e3679631 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1290,7 +1290,8 @@ do_collation_version_check(const ObjectAddress *otherObject,
 		return false;
 
 	/* Ask the provider for the current version.  Give up if unsupported. */
-	current_version = get_collation_version_for_oid(otherObject->objectId);
+	current_version = get_collation_version_for_oid(otherObject->objectId,
+													false);
 	if (!current_version)
 		return false;
 
@@ -1369,7 +1370,7 @@ do_collation_version_update(const ObjectAddress *otherObject,
 	if (OidIsValid(*coll) && otherObject->objectId != *coll)
 		return false;
 
-	*new_version = get_collation_version_for_oid(otherObject->objectId);
+	*new_version = get_collation_version_for_oid(otherObject->objectId, false);
 
 	return true;
 }
diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
index 63da24322d..362db7fe91 100644
--- a/src/backend/catalog/pg_depend.c
+++ b/src/backend/catalog/pg_depend.c
@@ -116,7 +116,8 @@ recordMultipleDependencies(const ObjectAddress *depender,
 					referenced->objectId == POSIX_COLLATION_OID)
 					continue;
 
-				version = get_collation_version_for_oid(referenced->objectId);
+				version = get_collation_version_for_oid(referenced->objectId,
+														false);
 
 				/*
 				 * Default collation is pinned, so we need to force recording
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 9634ae6809..a7ee452e19 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -273,7 +273,7 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
 
-	version = get_collation_version_for_oid(collid);
+	version = get_collation_version_for_oid(collid, true);
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index e9c1231f9b..34b82b9335 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1726,10 +1726,11 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 /*
  * Get provider-specific collation version string for a given collation OID.
  * Return NULL if the provider doesn't support versions, or the collation is
- * unversioned (for example "C").
+ * unversioned (for example "C").  Unknown OIDs result in NULL if missing_ok is
+ * true.
  */
 char *
-get_collation_version_for_oid(Oid oid)
+get_collation_version_for_oid(Oid oid, bool missing_ok)
 {
 	HeapTuple	tp;
 	char	   *version;
@@ -1751,7 +1752,11 @@ get_collation_version_for_oid(Oid oid)
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(oid));
 		if (!HeapTupleIsValid(tp))
+		{
+			if (missing_ok)
+				return NULL;
 			elog(ERROR, "cache lookup failed for collation %u", oid);
+		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 		version = get_collation_actual_version(collform->collprovider,
 											   NameStr(collform->collcollate));
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 34dff74bd1..5a37caefbe 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -103,7 +103,7 @@ typedef struct pg_locale_struct *pg_locale_t;
 
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
-extern char *get_collation_version_for_oid(Oid collid);
+extern char *get_collation_version_for_oid(Oid collid, bool missing_ok);
 
 #ifdef USE_ICU
 extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);
-- 
2.30.0

From b52fad59748cf669c509552676907fcb87de8aec Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:19:40 +1300
Subject: [PATCH v2 2/4] pg_collation_actual_version() ->
 pg_collation_current_version().

The new name seems a bit more natural.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 doc/src/sgml/func.sgml                         |  8 ++++----
 src/backend/commands/collationcmds.c           |  2 +-
 src/backend/utils/adt/pg_locale.c              | 14 +++++++-------
 src/include/catalog/pg_proc.dat                |  4 ++--
 src/test/regress/expected/collate.icu.utf8.out |  2 +-
 src/test/regress/sql/collate.icu.utf8.sql      |  2 +-
 6 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1ab31a9056..d8224272a5 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -26227,14 +26227,14 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
-         <primary>pg_collation_actual_version</primary>
+         <primary>pg_collation_current_version</primary>
         </indexterm>
-        <function>pg_collation_actual_version</function> ( <type>oid</type> )
+        <function>pg_collation_current_version</function> ( <type>oid</type> )
         <returnvalue>text</returnvalue>
        </para>
        <para>
-        Returns the actual version of the collation object as it is currently
-        installed in the operating system.  <literal>null</literal> is returned
+        Returns the version of the collation object as reported by the ICU
+        library or operating system.  <literal>null</literal> is returned
         on operating systems where <productname>PostgreSQL</productname>
         doesn't have support for versions.
        </para></entry>
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index a7ee452e19..4b76a6051d 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -268,7 +268,7 @@ IsThereCollationInNamespace(const char *collname, Oid nspOid)
 }
 
 Datum
-pg_collation_actual_version(PG_FUNCTION_ARGS)
+pg_collation_current_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 34b82b9335..2e4c6e9a26 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -127,8 +127,8 @@ static char *IsoLocaleName(const char *);	/* MSVC specific */
 static void icu_set_collation_attributes(UCollator *collator, const char *loc);
 #endif
 
-static char *get_collation_actual_version(char collprovider,
-										  const char *collcollate);
+static char *get_collation_current_version(char collprovider,
+										   const char *collcollate);
 
 /*
  * pg_perm_setlocale
@@ -1610,7 +1610,7 @@ pg_newlocale_from_collation(Oid collid)
  * the operating system/library.
  */
 static char *
-get_collation_actual_version(char collprovider, const char *collcollate)
+get_collation_current_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
@@ -1743,8 +1743,8 @@ get_collation_version_for_oid(Oid oid, bool missing_ok)
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
 		dbform = (Form_pg_database) GETSTRUCT(tp);
-		version = get_collation_actual_version(COLLPROVIDER_LIBC,
-											   NameStr(dbform->datcollate));
+		version = get_collation_current_version(COLLPROVIDER_LIBC,
+												NameStr(dbform->datcollate));
 	}
 	else
 	{
@@ -1758,8 +1758,8 @@ get_collation_version_for_oid(Oid oid, bool missing_ok)
 			elog(ERROR, "cache lookup failed for collation %u", oid);
 		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
-		version = get_collation_actual_version(collform->collprovider,
-											   NameStr(collform->collcollate));
+		version = get_collation_current_version(collform->collprovider,
+												NameStr(collform->collcollate));
 	}
 
 	ReleaseSysCache(tp);
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 1487710d59..16044125ba 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -11321,9 +11321,9 @@
 
 { oid => '3448',
   descr => 'get actual version of collation from operating system',
-  proname => 'pg_collation_actual_version', procost => '100',
+  proname => 'pg_collation_current_version', procost => '100',
   provolatile => 'v', prorettype => 'text', proargtypes => 'oid',
-  prosrc => 'pg_collation_actual_version' },
+  prosrc => 'pg_collation_current_version' },
 
 # system management/monitoring related functions
 { oid => '3353', descr => 'list files in the log directory',
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index bc3752e923..970638ed37 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -2018,7 +2018,7 @@ SELECT objid::regclass::text collate "C", refobjid::regcollation::text collate "
 CASE
 WHEN refobjid = 'default'::regcollation THEN 'XXX' -- depends on libc version support
 WHEN refobjversion IS NULL THEN 'version not tracked'
-WHEN refobjversion = pg_collation_actual_version(refobjid) THEN 'up to date'
+WHEN refobjversion = pg_collation_current_version(refobjid) THEN 'up to date'
 ELSE 'out of date'
 END AS version
 FROM pg_depend d
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 0de2ed8d85..be5b464ffa 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -820,7 +820,7 @@ SELECT objid::regclass::text collate "C", refobjid::regcollation::text collate "
 CASE
 WHEN refobjid = 'default'::regcollation THEN 'XXX' -- depends on libc version support
 WHEN refobjversion IS NULL THEN 'version not tracked'
-WHEN refobjversion = pg_collation_actual_version(refobjid) THEN 'up to date'
+WHEN refobjversion = pg_collation_current_version(refobjid) THEN 'up to date'
 ELSE 'out of date'
 END AS version
 FROM pg_depend d
-- 
2.30.0

From df2a4625f40c4469b2331f6485e607c9d25c23aa Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:36:43 +1300
Subject: [PATCH v2 3/4] Refactor get_collation_current_version().

The code paths for three different OSes finished up with three different
ways of excluding C[.xxx] and POSIX from consideration.  Merge them.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/backend/utils/adt/pg_locale.c | 35 +++++--------------------------
 1 file changed, 5 insertions(+), 30 deletions(-)

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 2e4c6e9a26..697d518e63 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1636,37 +1636,18 @@ get_collation_current_version(char collprovider, const char *collcollate)
 	}
 	else
 #endif
-	if (collprovider == COLLPROVIDER_LIBC)
+	if (collprovider == COLLPROVIDER_LIBC &&
+		pg_strcasecmp("C", collcollate) != 0 &&
+		pg_strncasecmp("C.", collcollate, 2) != 0 &&
+		pg_strcasecmp("POSIX", collcollate) != 0 &&
+		pg_strncasecmp("POSIX.", collcollate, 6) != 0)
 	{
 #if defined(__GLIBC__)
-		char	   *copy = pstrdup(collcollate);
-		char	   *copy_suffix = strstr(copy, ".");
-		bool		need_version = true;
-
-		/*
-		 * Check for names like C.UTF-8 by chopping off the encoding suffix on
-		 * our temporary copy, so we can skip the version.
-		 */
-		if (copy_suffix)
-			*copy_suffix = '\0';
-		if (pg_strcasecmp("c", copy) == 0 ||
-			pg_strcasecmp("posix", copy) == 0)
-			need_version = false;
-		pfree(copy);
-		if (!need_version)
-			return NULL;
-
 		/* Use the glibc version because we don't have anything better. */
 		collversion = pstrdup(gnu_get_libc_version());
 #elif defined(LC_VERSION_MASK)
 		locale_t    loc;
 
-		/* C[.encoding] and POSIX never change. */
-		if (strcmp("C", collcollate) == 0 ||
-			strncmp("C.", collcollate, 2) == 0 ||
-			strcmp("POSIX", collcollate) == 0)
-			return NULL;
-
 		/* Look up FreeBSD collation version. */
 		loc = newlocale(LC_COLLATE, collcollate, NULL);
 		if (loc)
@@ -1687,12 +1668,6 @@ get_collation_current_version(char collprovider, const char *collcollate)
 		NLSVERSIONINFOEX version = {sizeof(NLSVERSIONINFOEX)};
 		WCHAR		wide_collcollate[LOCALE_NAME_MAX_LENGTH];
 
-		/* These would be invalid arguments, but have no version. */
-		if (pg_strcasecmp("c", collcollate) == 0 ||
-			pg_strcasecmp("posix", collcollate) == 0)
-			return NULL;
-
-		/* For all other names, ask the OS. */
 		MultiByteToWideChar(CP_ACP, 0, collcollate, -1, wide_collcollate,
 							LOCALE_NAME_MAX_LENGTH);
 		if (!GetNLSVersionEx(COMPARE_STRING, wide_collcollate, &version))
-- 
2.30.0

From 721a943dd86071a93089b8c6edd6a77b93ec8b60 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 15:05:04 +1300
Subject: [PATCH v2 4/4] Tab-complete CREATE COLLATION.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/bin/psql/tab-complete.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index b64db82f02..578e59ea2c 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -2433,6 +2433,20 @@ psql_completion(const char *text, int start, int end)
 	else if (Matches("CREATE", "ACCESS", "METHOD", MatchAny, "TYPE", MatchAny))
 		COMPLETE_WITH("HANDLER");
 
+	/* CREATE COLLATION */
+	else if (Matches("CREATE", "COLLATION", MatchAny))
+		COMPLETE_WITH("(");
+	else if (HeadMatches("CREATE", "COLLATION"))
+	{
+		if (TailMatches("(|*,"))
+			COMPLETE_WITH("LOCALE =", "LC_COLLATE =", "LC_CTYPE =",
+						  "PROVIDER =", "DETERMINISTIC =");
+		else if (TailMatches("PROVIDER", "="))
+			COMPLETE_WITH("libc", "icu");
+		else if (TailMatches("DETERMINISTIC", "="))
+			COMPLETE_WITH("true", "false");
+	}
+
 	/* CREATE DATABASE */
 	else if (Matches("CREATE", "DATABASE", MatchAny))
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
-- 
2.30.0

From 1a3092e6ca386bac3292aa60c20e3b2a2ce08fff Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:10:40 +1300
Subject: [PATCH v3 1/4] Hide internal error for
 pg_collation_actual_version(<bad OID>).

Instead of an unsightly internal "cache lookup failed" message, just
return NULL for bad OIDs, as seems to be the convention for other
similar things.

Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/backend/catalog/index.c                    |  5 +++--
 src/backend/catalog/pg_depend.c                |  3 ++-
 src/backend/commands/collationcmds.c           |  2 +-
 src/backend/utils/adt/pg_locale.c              |  9 +++++++--
 src/include/utils/pg_locale.h                  |  2 +-
 src/test/regress/expected/collate.icu.utf8.out | 14 ++++++++++++++
 src/test/regress/sql/collate.icu.utf8.sql      |  5 +++++
 7 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index b4ab0b88ad..a9e3679631 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1290,7 +1290,8 @@ do_collation_version_check(const ObjectAddress *otherObject,
 		return false;
 
 	/* Ask the provider for the current version.  Give up if unsupported. */
-	current_version = get_collation_version_for_oid(otherObject->objectId);
+	current_version = get_collation_version_for_oid(otherObject->objectId,
+													false);
 	if (!current_version)
 		return false;
 
@@ -1369,7 +1370,7 @@ do_collation_version_update(const ObjectAddress *otherObject,
 	if (OidIsValid(*coll) && otherObject->objectId != *coll)
 		return false;
 
-	*new_version = get_collation_version_for_oid(otherObject->objectId);
+	*new_version = get_collation_version_for_oid(otherObject->objectId, false);
 
 	return true;
 }
diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
index 63da24322d..362db7fe91 100644
--- a/src/backend/catalog/pg_depend.c
+++ b/src/backend/catalog/pg_depend.c
@@ -116,7 +116,8 @@ recordMultipleDependencies(const ObjectAddress *depender,
 					referenced->objectId == POSIX_COLLATION_OID)
 					continue;
 
-				version = get_collation_version_for_oid(referenced->objectId);
+				version = get_collation_version_for_oid(referenced->objectId,
+														false);
 
 				/*
 				 * Default collation is pinned, so we need to force recording
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index 9634ae6809..a7ee452e19 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -273,7 +273,7 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
 
-	version = get_collation_version_for_oid(collid);
+	version = get_collation_version_for_oid(collid, true);
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index e9c1231f9b..34b82b9335 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1726,10 +1726,11 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 /*
  * Get provider-specific collation version string for a given collation OID.
  * Return NULL if the provider doesn't support versions, or the collation is
- * unversioned (for example "C").
+ * unversioned (for example "C").  Unknown OIDs result in NULL if missing_ok is
+ * true.
  */
 char *
-get_collation_version_for_oid(Oid oid)
+get_collation_version_for_oid(Oid oid, bool missing_ok)
 {
 	HeapTuple	tp;
 	char	   *version;
@@ -1751,7 +1752,11 @@ get_collation_version_for_oid(Oid oid)
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(oid));
 		if (!HeapTupleIsValid(tp))
+		{
+			if (missing_ok)
+				return NULL;
 			elog(ERROR, "cache lookup failed for collation %u", oid);
+		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 		version = get_collation_actual_version(collform->collprovider,
 											   NameStr(collform->collcollate));
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 34dff74bd1..5a37caefbe 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -103,7 +103,7 @@ typedef struct pg_locale_struct *pg_locale_t;
 
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
-extern char *get_collation_version_for_oid(Oid collid);
+extern char *get_collation_version_for_oid(Oid collid, bool missing_ok);
 
 #ifdef USE_ICU
 extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index bc3752e923..de70cb1212 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -2155,3 +2155,17 @@ DROP SCHEMA collate_tests CASCADE;
 RESET client_min_messages;
 -- leave a collation for pg_upgrade test
 CREATE COLLATION coll_icu_upgrade FROM "und-x-icu";
+-- Test user-visible function for inspecting versions
+SELECT pg_collation_actual_version('"en-x-icu"'::regcollation) is not null;
+ ?column? 
+----------
+ t
+(1 row)
+
+-- Invalid OIDs are silently ignored
+SELECT pg_collation_actual_version(0) is null;
+ ?column? 
+----------
+ t
+(1 row)
+
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 0de2ed8d85..dd5d208854 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -883,3 +883,8 @@ RESET client_min_messages;
 
 -- leave a collation for pg_upgrade test
 CREATE COLLATION coll_icu_upgrade FROM "und-x-icu";
+
+-- Test user-visible function for inspecting versions
+SELECT pg_collation_actual_version('"en-x-icu"'::regcollation) is not null;
+-- Invalid OIDs are silently ignored
+SELECT pg_collation_actual_version(0) is null;
-- 
2.30.0

From ff2f63d3a98b059edc2c0e868f0734c017ec3825 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:19:40 +1300
Subject: [PATCH v3 2/4] pg_collation_actual_version() ->
 pg_collation_current_version().

The new name seems a bit more natural.

Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 doc/src/sgml/func.sgml                         |  8 ++++----
 src/backend/commands/collationcmds.c           |  2 +-
 src/backend/utils/adt/pg_locale.c              | 14 +++++++-------
 src/include/catalog/pg_proc.dat                |  4 ++--
 src/test/regress/expected/collate.icu.utf8.out |  6 +++---
 src/test/regress/sql/collate.icu.utf8.sql      |  6 +++---
 6 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1ab31a9056..d8224272a5 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -26227,14 +26227,14 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
-         <primary>pg_collation_actual_version</primary>
+         <primary>pg_collation_current_version</primary>
         </indexterm>
-        <function>pg_collation_actual_version</function> ( <type>oid</type> )
+        <function>pg_collation_current_version</function> ( <type>oid</type> )
         <returnvalue>text</returnvalue>
        </para>
        <para>
-        Returns the actual version of the collation object as it is currently
-        installed in the operating system.  <literal>null</literal> is returned
+        Returns the version of the collation object as reported by the ICU
+        library or operating system.  <literal>null</literal> is returned
         on operating systems where <productname>PostgreSQL</productname>
         doesn't have support for versions.
        </para></entry>
diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
index a7ee452e19..4b76a6051d 100644
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -268,7 +268,7 @@ IsThereCollationInNamespace(const char *collname, Oid nspOid)
 }
 
 Datum
-pg_collation_actual_version(PG_FUNCTION_ARGS)
+pg_collation_current_version(PG_FUNCTION_ARGS)
 {
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 34b82b9335..2e4c6e9a26 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -127,8 +127,8 @@ static char *IsoLocaleName(const char *);	/* MSVC specific */
 static void icu_set_collation_attributes(UCollator *collator, const char *loc);
 #endif
 
-static char *get_collation_actual_version(char collprovider,
-										  const char *collcollate);
+static char *get_collation_current_version(char collprovider,
+										   const char *collcollate);
 
 /*
  * pg_perm_setlocale
@@ -1610,7 +1610,7 @@ pg_newlocale_from_collation(Oid collid)
  * the operating system/library.
  */
 static char *
-get_collation_actual_version(char collprovider, const char *collcollate)
+get_collation_current_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
@@ -1743,8 +1743,8 @@ get_collation_version_for_oid(Oid oid, bool missing_ok)
 		if (!HeapTupleIsValid(tp))
 			elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
 		dbform = (Form_pg_database) GETSTRUCT(tp);
-		version = get_collation_actual_version(COLLPROVIDER_LIBC,
-											   NameStr(dbform->datcollate));
+		version = get_collation_current_version(COLLPROVIDER_LIBC,
+												NameStr(dbform->datcollate));
 	}
 	else
 	{
@@ -1758,8 +1758,8 @@ get_collation_version_for_oid(Oid oid, bool missing_ok)
 			elog(ERROR, "cache lookup failed for collation %u", oid);
 		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
-		version = get_collation_actual_version(collform->collprovider,
-											   NameStr(collform->collcollate));
+		version = get_collation_current_version(collform->collprovider,
+												NameStr(collform->collcollate));
 	}
 
 	ReleaseSysCache(tp);
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 1487710d59..16044125ba 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -11321,9 +11321,9 @@
 
 { oid => '3448',
   descr => 'get actual version of collation from operating system',
-  proname => 'pg_collation_actual_version', procost => '100',
+  proname => 'pg_collation_current_version', procost => '100',
   provolatile => 'v', prorettype => 'text', proargtypes => 'oid',
-  prosrc => 'pg_collation_actual_version' },
+  prosrc => 'pg_collation_current_version' },
 
 # system management/monitoring related functions
 { oid => '3353', descr => 'list files in the log directory',
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index de70cb1212..43fbff1de2 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -2018,7 +2018,7 @@ SELECT objid::regclass::text collate "C", refobjid::regcollation::text collate "
 CASE
 WHEN refobjid = 'default'::regcollation THEN 'XXX' -- depends on libc version support
 WHEN refobjversion IS NULL THEN 'version not tracked'
-WHEN refobjversion = pg_collation_actual_version(refobjid) THEN 'up to date'
+WHEN refobjversion = pg_collation_current_version(refobjid) THEN 'up to date'
 ELSE 'out of date'
 END AS version
 FROM pg_depend d
@@ -2156,14 +2156,14 @@ RESET client_min_messages;
 -- leave a collation for pg_upgrade test
 CREATE COLLATION coll_icu_upgrade FROM "und-x-icu";
 -- Test user-visible function for inspecting versions
-SELECT pg_collation_actual_version('"en-x-icu"'::regcollation) is not null;
+SELECT pg_collation_current_version('"en-x-icu"'::regcollation) is not null;
  ?column? 
 ----------
  t
 (1 row)
 
 -- Invalid OIDs are silently ignored
-SELECT pg_collation_actual_version(0) is null;
+SELECT pg_collation_current_version(0) is null;
  ?column? 
 ----------
  t
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index dd5d208854..8b341dbb24 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -820,7 +820,7 @@ SELECT objid::regclass::text collate "C", refobjid::regcollation::text collate "
 CASE
 WHEN refobjid = 'default'::regcollation THEN 'XXX' -- depends on libc version support
 WHEN refobjversion IS NULL THEN 'version not tracked'
-WHEN refobjversion = pg_collation_actual_version(refobjid) THEN 'up to date'
+WHEN refobjversion = pg_collation_current_version(refobjid) THEN 'up to date'
 ELSE 'out of date'
 END AS version
 FROM pg_depend d
@@ -885,6 +885,6 @@ RESET client_min_messages;
 CREATE COLLATION coll_icu_upgrade FROM "und-x-icu";
 
 -- Test user-visible function for inspecting versions
-SELECT pg_collation_actual_version('"en-x-icu"'::regcollation) is not null;
+SELECT pg_collation_current_version('"en-x-icu"'::regcollation) is not null;
 -- Invalid OIDs are silently ignored
-SELECT pg_collation_actual_version(0) is null;
+SELECT pg_collation_current_version(0) is null;
-- 
2.30.0

From 5ebcead5e357a67d26a257c041e898002d0b16f7 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 14:36:43 +1300
Subject: [PATCH v3 3/4] Refactor get_collation_current_version().

The code paths for three different OSes finished up with three different
ways of excluding C[.xxx] and POSIX from consideration.  Merge them.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/backend/utils/adt/pg_locale.c | 34 ++++---------------------------
 1 file changed, 4 insertions(+), 30 deletions(-)

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 2e4c6e9a26..df1f36132d 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1636,37 +1636,17 @@ get_collation_current_version(char collprovider, const char *collcollate)
 	}
 	else
 #endif
-	if (collprovider == COLLPROVIDER_LIBC)
+	if (collprovider == COLLPROVIDER_LIBC &&
+		pg_strcasecmp("C", collcollate) != 0 &&
+		pg_strncasecmp("C.", collcollate, 2) != 0 &&
+		pg_strcasecmp("POSIX", collcollate) != 0)
 	{
 #if defined(__GLIBC__)
-		char	   *copy = pstrdup(collcollate);
-		char	   *copy_suffix = strstr(copy, ".");
-		bool		need_version = true;
-
-		/*
-		 * Check for names like C.UTF-8 by chopping off the encoding suffix on
-		 * our temporary copy, so we can skip the version.
-		 */
-		if (copy_suffix)
-			*copy_suffix = '\0';
-		if (pg_strcasecmp("c", copy) == 0 ||
-			pg_strcasecmp("posix", copy) == 0)
-			need_version = false;
-		pfree(copy);
-		if (!need_version)
-			return NULL;
-
 		/* Use the glibc version because we don't have anything better. */
 		collversion = pstrdup(gnu_get_libc_version());
 #elif defined(LC_VERSION_MASK)
 		locale_t    loc;
 
-		/* C[.encoding] and POSIX never change. */
-		if (strcmp("C", collcollate) == 0 ||
-			strncmp("C.", collcollate, 2) == 0 ||
-			strcmp("POSIX", collcollate) == 0)
-			return NULL;
-
 		/* Look up FreeBSD collation version. */
 		loc = newlocale(LC_COLLATE, collcollate, NULL);
 		if (loc)
@@ -1687,12 +1667,6 @@ get_collation_current_version(char collprovider, const char *collcollate)
 		NLSVERSIONINFOEX version = {sizeof(NLSVERSIONINFOEX)};
 		WCHAR		wide_collcollate[LOCALE_NAME_MAX_LENGTH];
 
-		/* These would be invalid arguments, but have no version. */
-		if (pg_strcasecmp("c", collcollate) == 0 ||
-			pg_strcasecmp("posix", collcollate) == 0)
-			return NULL;
-
-		/* For all other names, ask the OS. */
 		MultiByteToWideChar(CP_ACP, 0, collcollate, -1, wide_collcollate,
 							LOCALE_NAME_MAX_LENGTH);
 		if (!GetNLSVersionEx(COMPARE_STRING, wide_collcollate, &version))
-- 
2.30.0

From bdaadc82251bb490d25cf55e4aaca4957d52e32d Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 17 Feb 2021 15:05:04 +1300
Subject: [PATCH v3 4/4] Tab-complete CREATE COLLATION.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com
---
 src/bin/psql/tab-complete.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index b64db82f02..62e1ccc397 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -981,6 +981,11 @@ static const SchemaQuery Query_for_list_of_statistics = {
 "   FROM pg_catalog.pg_cursors "\
 "  WHERE substring(pg_catalog.quote_ident(name),1,%d)='%s'"
 
+#define Query_for_list_of_collations \
+" SELECT pg_catalog.quote_ident(collname) "\
+"   FROM pg_catalog.pg_collation "\
+"  WHERE collencoding IN (-1, pg_catalog.pg_char_to_encoding(pg_catalog.getdatabaseencoding())) AND substring(pg_catalog.quote_ident(collname),1,%d)='%s'"
+
 /*
  * These object types were introduced later than our support cutoff of
  * server version 7.4.  We use the VersionedQuery infrastructure so that
@@ -1031,7 +1036,7 @@ static const pgsql_thing_t words_after_create[] = {
 	{"AGGREGATE", NULL, NULL, Query_for_list_of_aggregates},
 	{"CAST", NULL, NULL, NULL}, /* Casts have complex structures for names, so
 								 * skip it */
-	{"COLLATION", "SELECT pg_catalog.quote_ident(collname) FROM pg_catalog.pg_collation WHERE collencoding IN (-1, pg_catalog.pg_char_to_encoding(pg_catalog.getdatabaseencoding())) AND substring(pg_catalog.quote_ident(collname),1,%d)='%s'"},
+	{"COLLATION", Query_for_list_of_collations},
 
 	/*
 	 * CREATE CONSTRAINT TRIGGER is not supported here because it is designed
@@ -2433,6 +2438,22 @@ psql_completion(const char *text, int start, int end)
 	else if (Matches("CREATE", "ACCESS", "METHOD", MatchAny, "TYPE", MatchAny))
 		COMPLETE_WITH("HANDLER");
 
+	/* CREATE COLLATION */
+	else if (Matches("CREATE", "COLLATION", MatchAny))
+		COMPLETE_WITH("(", "FROM");
+	else if (Matches("CREATE", "COLLATION", MatchAny, "FROM"))
+		COMPLETE_WITH_QUERY(Query_for_list_of_collations);
+	else if (HeadMatches("CREATE", "COLLATION", MatchAny, "(*"))
+	{
+		if (TailMatches("(|*,"))
+			COMPLETE_WITH("LOCALE =", "LC_COLLATE =", "LC_CTYPE =",
+						  "PROVIDER =", "DETERMINISTIC =");
+		else if (TailMatches("PROVIDER", "="))
+			COMPLETE_WITH("libc", "icu");
+		else if (TailMatches("DETERMINISTIC", "="))
+			COMPLETE_WITH("true", "false");
+	}
+
 	/* CREATE DATABASE */
 	else if (Matches("CREATE", "DATABASE", MatchAny))
 		COMPLETE_WITH("OWNER", "TEMPLATE", "ENCODING", "TABLESPACE",
-- 
2.30.0