gh-88091: Fix unicodedata.decomposition() for Hangul Syllables (GH-144993)

Author: StanFromIreland

Lib/test/test_unicodedata.py

@@ -378,6 +378,12 @@ def test_decomposition(self):
         # New in 17.0.0
         self.assertEqual(self.db.decomposition('\uA7F1'), '' if self.old else '<super> 0053')
 
+        # Hangul characters
+        self.assertEqual(self.db.decomposition('\uAC00'), '1100 1161')
+        self.assertEqual(self.db.decomposition('\uD4DB'), '1111 1171 11B6')
+        self.assertEqual(self.db.decomposition('\uC2F8'), '110A 1161')
+        self.assertEqual(self.db.decomposition('\uD7A3'), '1112 1175 11C2')
+
         self.assertRaises(TypeError, self.db.decomposition)
         self.assertRaises(TypeError, self.db.decomposition, 'xx')
 
@@ -687,9 +693,9 @@ class UnicodeFunctionsTest(unittest.TestCase, BaseUnicodeFunctionsTest):
 
     # Update this if the database changes. Make sure to do a full rebuild
     # (e.g. 'make distclean && make') to get the correct checksum.
-    expectedchecksum = ('668dbbea1136e69d4f00677a5988b23bc78aefc6'
+    expectedchecksum = ('00b13fa975a60b1d3f490f1fc8c126ab24990c75'
                         if quicktest else
-                        'b869af769bd8fe352c04622ab90533dc54df5cf3')
+                        'ebfc9dd281c2226998fd435744dd2e9321899beb')
 
     @requires_resource('network')
     def test_all_names(self):
@@ -1068,9 +1074,9 @@ def test_block_invalid_input(self):
 class Unicode_3_2_0_FunctionsTest(unittest.TestCase, BaseUnicodeFunctionsTest):
     db = unicodedata.ucd_3_2_0
     old = True
-    expectedchecksum = ('2164a66700e03cba9c9f5ed9e9a8d594d2da136a'
+    expectedchecksum = ('cb5bbbd1f55b67371e18222b90a8e21c87f16b72'
                         if quicktest else
-                        'a8276cec9b6991779c5bdaa46c1ae7cc50bc2403')
+                        '74936dffe949d99203a47e6a66565b2fc337bae7')
 
 
 class UnicodeMiscTest(unittest.TestCase):

Misc/NEWS.d/next/Library/2026-02-19-10-57-40.gh-issue-88091.N7qGV-.rst

@@ -0,0 +1 @@
+Fix :func:`unicodedata.decomposition` for Hangul characters.

Modules/unicodedata.c

@@ -429,6 +429,17 @@ unicodedata_UCD_east_asian_width_impl(PyObject *self, int chr)
     return PyUnicode_FromString(_PyUnicode_EastAsianWidthNames[index]);
 }
 
+// For Hangul decomposition
+#define SBase   0xAC00
+#define LBase   0x1100
+#define VBase   0x1161
+#define TBase   0x11A7
+#define LCount  19
+#define VCount  21
+#define TCount  28
+#define NCount  (VCount*TCount)
+#define SCount  (LCount*NCount)
+
 /*[clinic input]
 @permit_long_summary
 unicodedata.UCD.decomposition
@@ -460,6 +471,25 @@ unicodedata_UCD_decomposition_impl(PyObject *self, int chr)
             return Py_GetConstant(Py_CONSTANT_EMPTY_STR); /* unassigned */
     }
 
+    // Hangul Decomposition.
+    // See section 3.12.2, "Hangul Syllable Decomposition"
+    // https://www.unicode.org/versions/latest/core-spec/chapter-3/#G56669
+    if (SBase <= code && code < (SBase + SCount)) {
+        int SIndex = code - SBase;
+        int L = LBase + SIndex / NCount;
+        int V = VBase + (SIndex % NCount) / TCount;
+        int T = TBase + SIndex % TCount;
+        if (T != TBase) {
+            PyOS_snprintf(decomp, sizeof(decomp),
+                          "%04X %04X %04X", L, V, T);
+        }
+        else {
+            PyOS_snprintf(decomp, sizeof(decomp),
+                          "%04X %04X", L, V);
+        }
+        return PyUnicode_FromString(decomp);
+    }
+
     if (code < 0 || code >= 0x110000)
         index = 0;
     else {
@@ -522,16 +552,6 @@ get_decomp_record(PyObject *self, Py_UCS4 code,
     (*index)++;
 }
 
-#define SBase   0xAC00
-#define LBase   0x1100
-#define VBase   0x1161
-#define TBase   0x11A7
-#define LCount  19
-#define VCount  21
-#define TCount  28
-#define NCount  (VCount*TCount)
-#define SCount  (LCount*NCount)
-
 static PyObject*
 nfd_nfkd(PyObject *self, PyObject *input, int k)
 {
@@ -585,7 +605,9 @@ nfd_nfkd(PyObject *self, PyObject *input, int k)
                 }
                 output = new_output;
             }
-            /* Hangul Decomposition. */
+            // Hangul Decomposition.
+            // See section 3.12.2, "Hangul Syllable Decomposition"
+            // https://www.unicode.org/versions/latest/core-spec/chapter-3/#G56669
             if (SBase <= code && code < (SBase+SCount)) {
                 int SIndex = code - SBase;
                 int L = LBase + SIndex / NCount;