From 785323a138398465bb10e8ecdda5fef9cd19edd1 Mon Sep 17 00:00:00 2001
From: Jeff Davis <jeff@j-davis.com>
Date: Thu, 4 Dec 2025 10:38:11 -0800
Subject: [PATCH v12 4/8] 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.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com
---
 contrib/ltree/crc32.c     | 46 ++++++++++++++++++++++++++++++++-------
 contrib/ltree/lquery_op.c | 39 ++++++++++++++++++++++++++++++---
 2 files changed, 74 insertions(+), 11 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 d58e34769b8..8abd0de1a9c 100644
--- a/contrib/ltree/lquery_op.c
+++ b/contrib/ltree/lquery_op.c
@@ -94,11 +94,44 @@ ltree_prefix_eq(const char *a, size_t a_sz, const char *b, size_t b_sz)
 bool
 ltree_prefix_eq_ci(const char *a, size_t a_sz, const char *b, size_t b_sz)
 {
-	char	   *al = str_tolower(a, a_sz, DEFAULT_COLLATION_OID);
-	char	   *bl = str_tolower(b, b_sz, DEFAULT_COLLATION_OID);
+	static pg_locale_t locale = NULL;
+	size_t		al_sz = a_sz + 1;
+	size_t		al_len;
+	char	   *al = palloc(al_sz);
+	size_t		bl_sz = b_sz + 1;
+	size_t		bl_len;
+	char	   *bl = palloc(bl_sz);
 	bool		res;
 
-	res = (strncmp(al, bl, a_sz) == 0);
+	if (!locale)
+		locale = pg_database_locale();
+
+	/* casefold both a and b */
+
+	al_len = pg_strfold(al, al_sz, a, a_sz, locale);
+	if (al_len + 1 > al_sz)
+	{
+		/* grow buffer if needed and retry */
+		al_sz = al_len + 1;
+		al = repalloc(al, al_sz);
+		al_len = pg_strfold(al, al_sz, a, a_sz, locale);
+		Assert(al_len + 1 <= al_sz);
+	}
+
+	bl_len = pg_strfold(bl, bl_sz, b, b_sz, locale);
+	if (bl_len + 1 > bl_sz)
+	{
+		/* grow buffer if needed and retry */
+		bl_sz = bl_len + 1;
+		bl = repalloc(bl, bl_sz);
+		bl_len = pg_strfold(bl, bl_sz, b, b_sz, locale);
+		Assert(bl_len + 1 <= bl_sz);
+	}
+
+	if (al_len > bl_len)
+		res = false;
+	else
+		res = (strncmp(al, bl, al_len) == 0);
 
 	pfree(al);
 	pfree(bl);
-- 
2.43.0