0001-Fix-off-by-one-with-NFC-recomposition-for-Hangul-U-1.patch

From 0614fd3227eedffe91c31468def76400fd01d134 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 4 Jun 2026 12:56:36 +0900
Subject: [PATCH] Fix off-by-one with NFC recomposition for Hangul U+11A7
 (TBASE)

The NFC recomposition incorrectly included TBASE as a valid T syllable,
which is incorrect based on the Unicode spec (TBASE is one below the
start of the range, range beginning at U+11A8).

This would cause the TBASE to be silently swallowed in the
normalization, leading to an incorrect result.

A couple of regression tests are added to check more patterns with
Hangul recomposition and decomposition, on top of a test to check this
issue with TBASE.

Author: Diego Frias <mail@dzfrias.dev>
Discussion: https://postgr.es/m/B92ED640-7D4A-4505-B09F-3548F58CBB16@dzfrias.dev
Backpatch-through: 14
---
 src/common/unicode_norm.c             |  2 +-
 src/test/regress/expected/unicode.out | 78 +++++++++++++++++++++++++++
 src/test/regress/sql/unicode.sql      | 20 +++++++
 3 files changed, 99 insertions(+), 1 deletion(-)

diff --git a/src/common/unicode_norm.c b/src/common/unicode_norm.c
index cf84f2024140..0534ae34640f 100644
--- a/src/common/unicode_norm.c
+++ b/src/common/unicode_norm.c
@@ -236,7 +236,7 @@ recompose_code(uint32 start, uint32 code, uint32 *result)
 	/* Check if two current characters are LV and T */
 	else if (start >= SBASE && start < (SBASE + SCOUNT) &&
 			 ((start - SBASE) % TCOUNT) == 0 &&
-			 code >= TBASE && code < (TBASE + TCOUNT))
+			 code > TBASE && code < (TBASE + TCOUNT))
 	{
 		/* make syllable of form LVT */
 		uint32		tindex = code - TBASE;
diff --git a/src/test/regress/expected/unicode.out b/src/test/regress/expected/unicode.out
index 1e06de226491..63e48d3a961f 100644
--- a/src/test/regress/expected/unicode.out
+++ b/src/test/regress/expected/unicode.out
@@ -105,3 +105,81 @@ ORDER BY num;
 
 SELECT is_normalized('abc', 'def');  -- run-time error
 ERROR:  invalid normalization form: def
+-- Hangul NFC recomposition tests
+-- L+V -> LV composition (first and last)
+SELECT normalize(U&'\1100\1161', NFC) = U&'\AC00' COLLATE "C" AS hangul_lv_first;
+ hangul_lv_first 
+-----------------
+ t
+(1 row)
+
+SELECT normalize(U&'\1112\1175', NFC) = U&'\D788' COLLATE "C" AS hangul_lv_last;
+ hangul_lv_last 
+----------------
+ t
+(1 row)
+
+-- LV+T -> LVT composition
+SELECT normalize(U&'\AC00\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_lvt_first_t;
+ hangul_lvt_first_t 
+--------------------
+ t
+(1 row)
+
+SELECT normalize(U&'\AC00\11C2', NFC) = U&'\AC1B' COLLATE "C" AS hangul_lvt_last_t;
+ hangul_lvt_last_t 
+-------------------
+ t
+(1 row)
+
+SELECT normalize(U&'\D788\11A8', NFC) = U&'\D789' COLLATE "C" AS hangul_lvt_last_lv;
+ hangul_lvt_last_lv 
+--------------------
+ t
+(1 row)
+
+-- L+V+T -> LVT composition
+SELECT normalize(U&'\1100\1161\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_full_lvt;
+ hangul_full_lvt 
+-----------------
+ t
+(1 row)
+
+SELECT normalize(U&'\1112\1175\11C2', NFC) = U&'\D7A3' COLLATE "C" AS hangul_full_lvt;
+ hangul_full_lvt 
+-----------------
+ t
+(1 row)
+
+-- TBASE invalid T syllable
+SELECT normalize(U&'\AC00\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_tbase_not_combined;
+ hangul_tbase_not_combined 
+---------------------------
+ t
+(1 row)
+
+SELECT normalize(U&'\1100\1161\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_lv_tbase_separate;
+ hangul_lv_tbase_separate 
+--------------------------
+ t
+(1 row)
+
+-- Hangul NFD decomposition tests
+SELECT normalize(U&'\AC00', NFD) = U&'\1100\1161' COLLATE "C" AS hangul_nfd_lv;
+ hangul_nfd_lv 
+---------------
+ t
+(1 row)
+
+SELECT normalize(U&'\AC01', NFD) = U&'\1100\1161\11A8' COLLATE "C" AS hangul_nfd_lvt;
+ hangul_nfd_lvt 
+----------------
+ t
+(1 row)
+
+SELECT normalize(U&'\D7A3', NFD) = U&'\1112\1175\11C2' COLLATE "C" AS hangul_nfd_last;
+ hangul_nfd_last 
+-----------------
+ t
+(1 row)
+
diff --git a/src/test/regress/sql/unicode.sql b/src/test/regress/sql/unicode.sql
index e50adb68ed0d..951f86a336e8 100644
--- a/src/test/regress/sql/unicode.sql
+++ b/src/test/regress/sql/unicode.sql
@@ -36,3 +36,23 @@ FROM
 ORDER BY num;
 
 SELECT is_normalized('abc', 'def');  -- run-time error
+
+-- Hangul NFC recomposition tests
+-- L+V -> LV composition (first and last)
+SELECT normalize(U&'\1100\1161', NFC) = U&'\AC00' COLLATE "C" AS hangul_lv_first;
+SELECT normalize(U&'\1112\1175', NFC) = U&'\D788' COLLATE "C" AS hangul_lv_last;
+-- LV+T -> LVT composition
+SELECT normalize(U&'\AC00\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_lvt_first_t;
+SELECT normalize(U&'\AC00\11C2', NFC) = U&'\AC1B' COLLATE "C" AS hangul_lvt_last_t;
+SELECT normalize(U&'\D788\11A8', NFC) = U&'\D789' COLLATE "C" AS hangul_lvt_last_lv;
+-- L+V+T -> LVT composition
+SELECT normalize(U&'\1100\1161\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_full_lvt;
+SELECT normalize(U&'\1112\1175\11C2', NFC) = U&'\D7A3' COLLATE "C" AS hangul_full_lvt;
+-- TBASE invalid T syllable
+SELECT normalize(U&'\AC00\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_tbase_not_combined;
+SELECT normalize(U&'\1100\1161\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_lv_tbase_separate;
+
+-- Hangul NFD decomposition tests
+SELECT normalize(U&'\AC00', NFD) = U&'\1100\1161' COLLATE "C" AS hangul_nfd_lv;
+SELECT normalize(U&'\AC01', NFD) = U&'\1100\1161\11A8' COLLATE "C" AS hangul_nfd_lvt;
+SELECT normalize(U&'\D7A3', NFD) = U&'\1112\1175\11C2' COLLATE "C" AS hangul_nfd_last;
-- 
2.54.0