bpo-40000: Improve error messages when validating invalid ast.Constant nodes (GH-19055)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

Lib/test/test_ast.py

@@ -582,6 +582,15 @@ class AST_Tests(unittest.TestCase):
             compile(m, "<test>", "exec")
         self.assertIn("identifier must be of type str", str(cm.exception))
 
+    def test_invalid_constant(self):
+        for invalid_constant in int, (1, 2, int), frozenset((1, 2, int)):
+            e = ast.Expression(body=ast.Constant(invalid_constant))
+            ast.fix_missing_locations(e)
+            with self.assertRaisesRegex(
+                TypeError, "invalid type in Constant: type"
+            ):
+                compile(e, "<test>", "eval")
+
     def test_empty_yield_from(self):
         # Issue 16546: yield from value is not optional.
         empty_yield_from = ast.parse("def f():\n yield from g()")

Misc/NEWS.d/next/Library/2020-03-18-12-54-25.bpo-40000.FnsPZC.rst

@@ -0,0 +1,2 @@
+Improved error messages for validation of ``ast.Constant`` nodes. Patch by
+Batuhan Taskaya.

Python/ast.c

@@ -147,6 +147,11 @@ validate_constant(PyObject *value)
         return 1;
     }
 
+    if (!PyErr_Occurred()) {
+        PyErr_Format(PyExc_TypeError,
+                     "got an invalid type in Constant: %s",
+                     _PyType_Name(Py_TYPE(value)));
+    }
     return 0;
 }
 
@@ -261,9 +266,6 @@ validate_expr(expr_ty exp, expr_context_ty ctx)
             validate_keywords(exp->v.Call.keywords);
     case Constant_kind:
         if (!validate_constant(exp->v.Constant.value)) {
-            PyErr_Format(PyExc_TypeError,
-                         "got an invalid type in Constant: %s",
-                         _PyType_Name(Py_TYPE(exp->v.Constant.value)));
             return 0;
         }
         return 1;