bpo-40334: Fix test_peg_parser to actually use the old parser (GH-19778)

Now that the default parser is the new PEG parser, ast.parse uses it, which means that we don't actually test something in test_peg_parser. This commit introduces a new keyword argument (`oldparser`) for `_peg_parser.parse_string` for specifying that a string needs to be parsed with the old parser. This keyword argument is used in the tests to actually compare the ASTs the new parser generates with those generated by the old parser.

1 files changed, 11 insertions, 3 deletions

diff --git a/Modules/_peg_parser.c b/Modules/_peg_parser.c
index e1ec36e07b..59b80f9e06 100644
--- a/Modules/_peg_parser.c
+++ b/Modules/_peg_parser.c
@@ -45,11 +45,13 @@ error:
 PyObject *
 _Py_parse_string(PyObject *self, PyObject *args, PyObject *kwds)
 {
-    static char *keywords[] = {"string", "mode", NULL};
+    static char *keywords[] = {"string", "mode", "oldparser", NULL};
     char *the_string;
     char *mode_str = "exec";
+    int oldparser = 0;
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "s|s", keywords, &the_string, &mode_str)) {
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "s|sp", keywords,
+            &the_string, &mode_str, &oldparser)) {
         return NULL;
     }
 
@@ -77,7 +79,13 @@ _Py_parse_string(PyObject *self, PyObject *args, PyObject *kwds)
     PyCompilerFlags flags = _PyCompilerFlags_INIT;
     flags.cf_flags = PyCF_IGNORE_COOKIE;
 
-    mod_ty res = PyPegen_ASTFromString(the_string, mode, &flags, arena);
+    mod_ty res;
+    if (oldparser) {
+        res = PyParser_ASTFromString(the_string, "<string>", mode, &flags, arena);
+    }
+    else {
+        res = PyPegen_ASTFromString(the_string, mode, &flags, arena);
+    }
     if (res == NULL) {
         goto error;
     }