From dcd90b2751f4aaf11d6164ea9fec3309e0817125 Mon Sep 17 00:00:00 2001
From: Jeff Davis <jeff@j-davis.com>
Date: Wed, 19 Nov 2025 10:20:36 -0800
Subject: [PATCH v10 06/11] Fix inconsistency between ltree_strncasecmp() and
 ltree_crc32_sz().

Previously, ltree_strncasecmp() used lowercasing with the default
collation; while ltree_crc32_sz used tolower() directly. These were
equivalent only if the default collation provider was libc and the
encoding is single-byte.

Change both to use casefolding with the default collation.

Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com
---
 contrib/ltree/crc32.c     | 46 ++++++++++++++++++++++++++++++++-------
 contrib/ltree/lquery_op.c | 31 ++++++++++++++++++++++++--
 2 files changed, 67 insertions(+), 10 deletions(-)

diff --git a/contrib/ltree/crc32.c b/contrib/ltree/crc32.c
index 134f46a805e..3918d4a0ec2 100644
--- a/contrib/ltree/crc32.c
+++ b/contrib/ltree/crc32.c
@@ -10,31 +10,61 @@
 #include "postgres.h"
 #include "ltree.h"
 
+#include "crc32.h"
+#include "utils/pg_crc.h"
 #ifdef LOWER_NODE
-#include <ctype.h>
-#define TOLOWER(x)	tolower((unsigned char) (x))
-#else
-#define TOLOWER(x)	(x)
+#include "utils/pg_locale.h"
 #endif
 
-#include "crc32.h"
-#include "utils/pg_crc.h"
+#ifdef LOWER_NODE
 
 unsigned int
 ltree_crc32_sz(const char *buf, int size)
 {
 	pg_crc32	crc;
 	const char *p = buf;
+	static pg_locale_t locale = NULL;
+
+	if (!locale)
+		locale = pg_database_locale();
 
 	INIT_TRADITIONAL_CRC32(crc);
 	while (size > 0)
 	{
-		char		c = (char) TOLOWER(*p);
+		char		foldstr[UNICODE_CASEMAP_BUFSZ];
+		int			srclen = pg_mblen(p);
+		size_t		foldlen;
+
+		/* fold one codepoint at a time */
+		foldlen = pg_strfold(foldstr, UNICODE_CASEMAP_BUFSZ, p, srclen,
+							 locale);
+
+		COMP_TRADITIONAL_CRC32(crc, foldstr, foldlen);
+
+		size -= srclen;
+		p += srclen;
+	}
+	FIN_TRADITIONAL_CRC32(crc);
+	return (unsigned int) crc;
+}
+
+#else
 
-		COMP_TRADITIONAL_CRC32(crc, &c, 1);
+unsigned int
+ltree_crc32_sz(const char *buf, int size)
+{
+	pg_crc32	crc;
+	const char *p = buf;
+
+	INIT_TRADITIONAL_CRC32(crc);
+	while (size > 0)
+	{
+		COMP_TRADITIONAL_CRC32(crc, p, 1);
 		size--;
 		p++;
 	}
 	FIN_TRADITIONAL_CRC32(crc);
 	return (unsigned int) crc;
 }
+
+#endif							/* !LOWER_NODE */
diff --git a/contrib/ltree/lquery_op.c b/contrib/ltree/lquery_op.c
index a6466f575fd..d6754eb613f 100644
--- a/contrib/ltree/lquery_op.c
+++ b/contrib/ltree/lquery_op.c
@@ -77,10 +77,37 @@ compare_subnode(ltree_level *t, char *qn, int len, int (*cmpptr) (const char *,
 int
 ltree_strncasecmp(const char *a, const char *b, size_t s)
 {
-	char	   *al = str_tolower(a, s, DEFAULT_COLLATION_OID);
-	char	   *bl = str_tolower(b, s, DEFAULT_COLLATION_OID);
+	static pg_locale_t locale = NULL;
+	size_t		al_sz = s + 1;
+	char	   *al = palloc(al_sz);
+	size_t		bl_sz = s + 1;
+	char	   *bl = palloc(bl_sz);
+	size_t		needed;
 	int			res;
 
+	if (!locale)
+		locale = pg_database_locale();
+
+	needed = pg_strfold(al, al_sz, a, s, locale);
+	if (needed + 1 > al_sz)
+	{
+		/* grow buffer if needed and retry */
+		al_sz = needed + 1;
+		al = repalloc(al, al_sz);
+		needed = pg_strfold(al, al_sz, a, s, locale);
+		Assert(needed + 1 <= al_sz);
+	}
+
+	needed = pg_strfold(bl, bl_sz, b, s, locale);
+	if (needed + 1 > bl_sz)
+	{
+		/* grow buffer if needed and retry */
+		bl_sz = needed + 1;
+		bl = repalloc(bl, bl_sz);
+		needed = pg_strfold(bl, bl_sz, b, s, locale);
+		Assert(needed + 1 <= bl_sz);
+	}
+
 	res = strncmp(al, bl, s);
 
 	pfree(al);
-- 
2.43.0