gh-104482: Fix error handling bugs in ast.c

Misc/NEWS.d/next/Core and Builtins/2023-05-14-18-56-54.gh-issue-104482.yaQsv8.rst

@@ -0,0 +1 @@
+Fix two error handling bugs in ast.c's parsing of pattern matching statements.

Python/ast.c

@@ -580,7 +580,9 @@ validate_pattern(struct validator *state, pattern_ty p, int star_ok)
                     break;
                 }
             }
-
+            if (ret == 0) {
+                break;
+            }
             ret = validate_patterns(state, p->v.MatchMapping.patterns, /*star_ok=*/0);
             break;
         case MatchClass_kind:
@@ -619,7 +621,9 @@ validate_pattern(struct validator *state, pattern_ty p, int star_ok)
                     break;
                 }
             }
-
+            if (ret == 0) {
+                break;
+            }
             if (!validate_patterns(state, p->v.MatchClass.patterns, /*star_ok=*/0)) {
                 ret = 0;
                 break;

Python/compile.c

@@ -567,6 +567,7 @@ PyCodeObject *
 _PyAST_Compile(mod_ty mod, PyObject *filename, PyCompilerFlags *pflags,
                int optimize, PyArena *arena)
 {
+    assert(!PyErr_Occurred());
     struct compiler *c = new_compiler(mod, filename, pflags, optimize, arena);
     if (c == NULL) {
         return NULL;