gh-101955: Fix SystemError in possesive quantifier with alternative and group (GH-111362)

Co-authored-by: <wjssz@users.noreply.github.com>

3 files changed, 26 insertions, 0 deletions

diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index 1612fc7663e..0d3599be87f 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -2640,6 +2640,12 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.match("(?>(?:ab?c){1,3})", "aca").span(), (0, 2))
         self.assertEqual(re.match("(?:ab?c){1,3}+", "aca").span(), (0, 2))
 
+    def test_bug_gh101955(self):
+        # Possessive quantifier with nested alternative with capture groups
+        self.assertEqual(re.match('((x)|y|z)*+', 'xyz').groups(), ('z', 'x'))
+        self.assertEqual(re.match('((x)|y|z){3}+', 'xyz').groups(), ('z', 'x'))
+        self.assertEqual(re.match('((x)|y|z){3,}+', 'xyz').groups(), ('z', 'x'))
+
     @unittest.skipIf(multiprocessing is None, 'test requires multiprocessing')
     def test_regression_gh94675(self):
         pattern = re.compile(r'(?<=[({}])(((//[^\n]*)?[\n])([\000-\040])*)*'
diff --git a/Misc/NEWS.d/next/Library/2023-10-26-16-36-22.gh-issue-101955.Ixu3IF.rst b/Misc/NEWS.d/next/Library/2023-10-26-16-36-22.gh-issue-101955.Ixu3IF.rst
new file mode 100644
index 00000000000..89431010f78
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-10-26-16-36-22.gh-issue-101955.Ixu3IF.rst
@@ -0,0 +1,2 @@
+Fix SystemError when match regular expression pattern containing some
+combination of possessive quantifier, alternative and capture group.
diff --git a/Modules/_sre/sre_lib.h b/Modules/_sre/sre_lib.h
index 0c93f512110..af4bfc56083 100644
--- a/Modules/_sre/sre_lib.h
+++ b/Modules/_sre/sre_lib.h
@@ -1306,6 +1306,17 @@ dispatch:
                pointer */
             state->ptr = ptr;
 
+            /* Set state->repeat to non-NULL */
+            ctx->u.rep = repeat_pool_malloc(state);
+            if (!ctx->u.rep) {
+                RETURN_ERROR(SRE_ERROR_MEMORY);
+            }
+            ctx->u.rep->count = -1;
+            ctx->u.rep->pattern = NULL;
+            ctx->u.rep->prev = state->repeat;
+            ctx->u.rep->last_ptr = NULL;
+            state->repeat = ctx->u.rep;
+
             /* Initialize Count to 0 */
             ctx->count = 0;
 
@@ -1320,6 +1331,9 @@ dispatch:
                 }
                 else {
                     state->ptr = ptr;
+                    /* Restore state->repeat */
+                    state->repeat = ctx->u.rep->prev;
+                    repeat_pool_free(state, ctx->u.rep);
                     RETURN_FAILURE;
                 }
             }
@@ -1392,6 +1406,10 @@ dispatch:
                 }
             }
 
+            /* Restore state->repeat */
+            state->repeat = ctx->u.rep->prev;
+            repeat_pool_free(state, ctx->u.rep);
+
             /* Evaluate Tail */
             /* Jump to end of pattern indicated by skip, and then skip
                the SUCCESS op code that follows it. */