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.

diff --git a/Lib/test/test_peg_parser.py b/Lib/test/test_peg_parser.py
index ea4afa6e1797328e06a2c5cc7b80b754ccd3a6d5..43d30bae84984717051eba8c22ca4bcb962806d2 100644 (file)
--- a/Lib/test/test_peg_parser.py
+++ b/Lib/test/test_peg_parser.py
@@ -699,7 +699,7 @@ class ASTGenerationTest(unittest.TestCase):
         self.maxDiff = None
         for source in TEST_SOURCES:
             actual_ast = peg_parser.parse_string(source)
-            expected_ast = ast.parse(source)
+            expected_ast = peg_parser.parse_string(source, oldparser=True)
             self.assertEqual(
                 ast.dump(actual_ast, include_attributes=True),
                 ast.dump(expected_ast, include_attributes=True),
@@ -721,12 +721,11 @@ class ASTGenerationTest(unittest.TestCase):
                 f"Actual error message does not match expexted for {source}"
             )
 
-    @support.skip_if_new_parser("This tests nothing for now, since compile uses pegen as well")
     @unittest.expectedFailure
     def test_correct_but_known_to_fail_ast_generation_on_source_files(self) -> None:
         for source in GOOD_BUT_FAIL_SOURCES:
             actual_ast = peg_parser.parse_string(source)
-            expected_ast = ast.parse(source)
+            expected_ast = peg_parser.parse_string(source, oldparser=True)
             self.assertEqual(
                 ast.dump(actual_ast, include_attributes=True),
                 ast.dump(expected_ast, include_attributes=True),
@@ -736,7 +735,7 @@ class ASTGenerationTest(unittest.TestCase):
     def test_correct_ast_generation_without_pos_info(self) -> None:
         for source in GOOD_BUT_FAIL_SOURCES:
             actual_ast = peg_parser.parse_string(source)
-            expected_ast = ast.parse(source)
+            expected_ast = peg_parser.parse_string(source, oldparser=True)
             self.assertEqual(
                 ast.dump(actual_ast),
                 ast.dump(expected_ast),
@@ -752,7 +751,7 @@ class ASTGenerationTest(unittest.TestCase):
     def test_correct_ast_generatrion_eval(self) -> None:
         for source in EXPRESSIONS_TEST_SOURCES:
             actual_ast = peg_parser.parse_string(source, mode='eval')
-            expected_ast = ast.parse(source, mode='eval')
+            expected_ast = peg_parser.parse_string(source, mode='eval', oldparser=True)
             self.assertEqual(
                 ast.dump(actual_ast, include_attributes=True),
                 ast.dump(expected_ast, include_attributes=True),

diff --git a/Modules/_peg_parser.c b/Modules/_peg_parser.c
index e1ec36e07bd57fd9cc7c62f9a99474828270de69..59b80f9e06e9e3fdd2d5c3225769f1710789b139 100644 (file)
--- 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;
     }