From 7e5e0de5a77b4f69cb9a3273470f3e5a4ec5a025 Mon Sep 17 00:00:00 2001
From: Nitin Motiani <nitinmotiani@google.com>
Date: Thu, 14 May 2026 10:49:54 +0000
Subject: [PATCH v1] Fix LIKE matching with nondeterministic collations and
 backslashes

Commit 85b7efa1cd added support for LIKE with nondeterministic
collations, but it included a bug in the unescaping logic for pattern
partitions. When the pattern contained a literal backslash (which is
represented as '\\' in the internal pattern), the code would skip both
backslashes, resulting in an incorrect match failure against the
original text.

This fix ensures that an escape backslash correctly causes the following
character to be copied literally into the subpattern before comparison.

A regression test is added to verify the fix and prevent future
regressions.

Reported-by: b/19474 on pgsql-bugs
---
 src/backend/utils/adt/like_match.c             | 5 ++---
 src/test/regress/expected/collate.icu.utf8.out | 7 +++++++
 src/test/regress/sql/collate.icu.utf8.sql      | 3 +++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/adt/like_match.c b/src/backend/utils/adt/like_match.c
index f5f72b82e21..149538cafbc 100644
--- a/src/backend/utils/adt/like_match.c
+++ b/src/backend/utils/adt/like_match.c
@@ -257,9 +257,8 @@ MatchText(const char *t, int tlen, const char *p, int plen, pg_locale_t locale)
 				for (const char *c = p; c < p1; c++)
 				{
 					if (*c == '\\')
-						;
-					else
-						*(b++) = *c;
+						c++;
+					*(b++) = *c;
 				}
 
 				subpat = buf;
diff --git a/src/test/regress/expected/collate.icu.utf8.out b/src/test/regress/expected/collate.icu.utf8.out
index 04e2f6df037..3ee7580b05d 100644
--- a/src/test/regress/expected/collate.icu.utf8.out
+++ b/src/test/regress/expected/collate.icu.utf8.out
@@ -2741,6 +2741,13 @@ SELECT U&'\0061\0308bc' LIKE U&'_\00e4bc' COLLATE ignore_accents;
 -- escape character at end of pattern
 SELECT 'foox' LIKE 'foo\' COLLATE ignore_accents;
 ERROR:  LIKE pattern must not end with escape character
+-- literal backslash with nondeterministic collation (bug #19474)
+SELECT 'back\slash' COLLATE ignore_accents LIKE 'back\slash%' ESCAPE '#';
+ ?column? 
+----------
+ t
+(1 row)
+
 -- foreign keys (mixing different nondeterministic collations not allowed)
 CREATE TABLE test10pk (x text COLLATE case_sensitive PRIMARY KEY);
 CREATE TABLE test10fk (x text COLLATE case_insensitive REFERENCES test10pk (x) ON UPDATE CASCADE ON DELETE CASCADE);  -- error
diff --git a/src/test/regress/sql/collate.icu.utf8.sql b/src/test/regress/sql/collate.icu.utf8.sql
index 18c47e6e05a..7810e56da6e 100644
--- a/src/test/regress/sql/collate.icu.utf8.sql
+++ b/src/test/regress/sql/collate.icu.utf8.sql
@@ -960,6 +960,9 @@ SELECT U&'\0061\0308bc' LIKE U&'_\00e4bc' COLLATE ignore_accents;
 -- escape character at end of pattern
 SELECT 'foox' LIKE 'foo\' COLLATE ignore_accents;
 
+-- literal backslash with nondeterministic collation (bug #19474)
+SELECT 'back\slash' COLLATE ignore_accents LIKE 'back\slash%' ESCAPE '#';
+
 -- foreign keys (mixing different nondeterministic collations not allowed)
 CREATE TABLE test10pk (x text COLLATE case_sensitive PRIMARY KEY);
 CREATE TABLE test10fk (x text COLLATE case_insensitive REFERENCES test10pk (x) ON UPDATE CASCADE ON DELETE CASCADE);  -- error
-- 
2.54.0.563.g4f69b47b94-goog

