bpo-43908: Apply Py_TPFLAGS_IMMUTABLETYPE to re types

Author: Erlend E. Aasland

Modules/_sre.c

@@ -2690,7 +2690,7 @@ static PyType_Spec pattern_spec = {
     .name = "re.Pattern",
     .basicsize = sizeof(PatternObject),
     .itemsize = sizeof(SRE_CODE),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE,
     .slots = pattern_slots,
 };
 
@@ -2755,7 +2755,7 @@ static PyType_Spec match_spec = {
     .name = "re.Match",
     .basicsize = sizeof(MatchObject),
     .itemsize = sizeof(Py_ssize_t),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE,
     .slots = match_slots,
 };
 
@@ -2781,7 +2781,7 @@ static PyType_Slot scanner_slots[] = {
 static PyType_Spec scanner_spec = {
     .name = "_" SRE_MODULE ".SRE_Scanner",
     .basicsize = sizeof(ScannerObject),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE,
     .slots = scanner_slots,
 };