From 9a500e02535b09051816a55ebb6f75e4421da270 Mon Sep 17 00:00:00 2001
From: steve-chavez <stevechavezast@gmail.com>
Date: Mon, 1 Dec 2025 20:13:36 -0500
Subject: [PATCH 1/2] refactor: isolate relation errors to a function

Also add levenshtein_is_absurd explaining more about the formula used.
---
 src/backend/parser/parse_relation.c | 74 ++++++++++++++++-------------
 1 file changed, 40 insertions(+), 34 deletions(-)

diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
index d544a69fc80..c1563f1b51b 100644
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -101,6 +101,8 @@ static int	specialAttNum(const char *attname);
 static bool rte_visible_if_lateral(ParseState *pstate, RangeTblEntry *rte);
 static bool rte_visible_if_qualified(ParseState *pstate, RangeTblEntry *rte);
 
+static inline bool levenshtein_is_absurd(int distance, int matchlen);
+static void errorMissingRelation(ParseState *pstate, const RangeVar *relation);
 
 /*
  * refnameNamespaceItem
@@ -615,11 +617,7 @@ updateFuzzyAttrMatchState(int fuzzy_rte_penalty,
 									  - fuzzy_rte_penalty,
 									  true);
 
-	/*
-	 * If more than half the characters are different, don't treat it as a
-	 * match, to avoid making ridiculous suggestions.
-	 */
-	if (columndistance > matchlen / 2)
+	if (levenshtein_is_absurd(columndistance, matchlen))
 		return;
 
 	/*
@@ -1416,6 +1414,31 @@ buildNSItemFromLists(RangeTblEntry *rte, Index rtindex,
 	return nsitem;
 }
 
+void
+errorMissingRelation(ParseState *pstate, const RangeVar *relation)
+{
+	/*
+	 * An unqualified name might have been meant as a reference to
+	 * some not-yet-in-scope CTE.  The bare "does not exist" message
+	 * has proven remarkably unhelpful for figuring out such problems,
+	 * so we take pains to offer a specific hint.
+	 */
+	if (isFutureCTE(pstate, relation->relname))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_TABLE),
+				 errmsg("relation \"%s\" does not exist",
+						relation->relname),
+				 errdetail("There is a WITH item named \"%s\", but it cannot be referenced from this part of the query.",
+						   relation->relname),
+				 errhint("Use WITH RECURSIVE, or re-order the WITH items to remove forward references.")));
+	else
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_TABLE),
+				 relation->schemaname ?
+					errmsg("relation \"%s.%s\" does not exist", relation->schemaname, relation->relname) :
+					errmsg("relation \"%s\" does not exist", relation->relname)));
+}
+
 /*
  * Open a table during parse analysis
  *
@@ -1436,35 +1459,7 @@ parserOpenTable(ParseState *pstate, const RangeVar *relation, int lockmode)
 	setup_parser_errposition_callback(&pcbstate, pstate, relation->location);
 	rel = table_openrv_extended(relation, lockmode, true);
 	if (rel == NULL)
-	{
-		if (relation->schemaname)
-			ereport(ERROR,
-					(errcode(ERRCODE_UNDEFINED_TABLE),
-					 errmsg("relation \"%s.%s\" does not exist",
-							relation->schemaname, relation->relname)));
-		else
-		{
-			/*
-			 * An unqualified name might have been meant as a reference to
-			 * some not-yet-in-scope CTE.  The bare "does not exist" message
-			 * has proven remarkably unhelpful for figuring out such problems,
-			 * so we take pains to offer a specific hint.
-			 */
-			if (isFutureCTE(pstate, relation->relname))
-				ereport(ERROR,
-						(errcode(ERRCODE_UNDEFINED_TABLE),
-						 errmsg("relation \"%s\" does not exist",
-								relation->relname),
-						 errdetail("There is a WITH item named \"%s\", but it cannot be referenced from this part of the query.",
-								   relation->relname),
-						 errhint("Use WITH RECURSIVE, or re-order the WITH items to remove forward references.")));
-			else
-				ereport(ERROR,
-						(errcode(ERRCODE_UNDEFINED_TABLE),
-						 errmsg("relation \"%s\" does not exist",
-								relation->relname)));
-		}
-	}
+		errorMissingRelation(pstate, relation);
 	cancel_parser_errposition_callback(&pcbstate);
 	return rel;
 }
@@ -3971,3 +3966,14 @@ getRTEPermissionInfo(List *rteperminfos, RangeTblEntry *rte)
 
 	return perminfo;
 }
+
+
+/*
+ * Ignore absurd suggestions (e.g., mostly different characters).
+ * Having MAX_FUZZY_DISTANCE = 3, `abc` and `xyz` have a levenshtein distance of 3 which falls under MAX_FUZZY_DISTANCE, but yet they're mostly different.
+ */
+static inline bool
+levenshtein_is_absurd(int distance, int matchlen)
+{
+	return distance > matchlen / 2;
+}
-- 
2.42.0