Better error messages for illegal bounds/constraints

JelleZijlstra · JelleZijlstra · commit 17c80600d615 · 2023-04-29T17:43:53.000-07:00
diff --git a/Grammar/python.gram b/Grammar/python.gram
@@ -646,7 +646,17 @@ type_param_seq[asdl_typeparam_seq*]: a[asdl_typeparam_seq*]=','.type_param+ [','
 
 type_param[typeparam_ty] (memo):
     | a=NAME b=[type_param_bound] { _PyAST_TypeVar(a->v.Name.id, b, EXTRA) }
+    | '*' a=NAME colon=":" e=expression {
+            RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
+                ? "cannot use constraints with TypeVarTuple"
+                : "cannot use bound with TypeVarTuple")
+        }
     | '*' a=NAME { _PyAST_TypeVarTuple(a->v.Name.id, EXTRA) }
+    | '**' a=NAME colon=":" e=expression {
+            RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
+                ? "cannot use constraints with ParamSpec"
+                : "cannot use bound with ParamSpec")
+        }
     | '**' a=NAME { _PyAST_ParamSpec(a->v.Name.id, EXTRA) }
 
 type_param_bound[expr_ty]: ":" e=expression { e }
diff --git a/Lib/test/test_type_params.py b/Lib/test/test_type_params.py
@@ -452,8 +452,18 @@ async def coroutine[B]():
 
 class TypeParamsTypeVarTupleTest(unittest.TestCase):
     def test_typevartuple_01(self):
-        code = """def func1[*A: str](): return (A, B, C)"""
-        check_syntax_error(self, code, r"expected '\('")
+        code = """def func1[*A: str](): pass"""
+        check_syntax_error(self, code, "cannot use bound with TypeVarTuple")
+        code = """def func1[*A: (int, str)](): pass"""
+        check_syntax_error(self, code, "cannot use constraints with TypeVarTuple")
+        code = """class X[*A: str]: pass"""
+        check_syntax_error(self, code, "cannot use bound with TypeVarTuple")
+        code = """class X[*A: (int, str)]: pass"""
+        check_syntax_error(self, code, "cannot use constraints with TypeVarTuple")
+        code = """type X[*A: str] = int"""
+        check_syntax_error(self, code, "cannot use bound with TypeVarTuple")
+        code = """type X[*A: (int, str)] = int"""
+        check_syntax_error(self, code, "cannot use constraints with TypeVarTuple")
 
     def test_typevartuple_02(self):
         def func1[*A]():
@@ -465,8 +475,18 @@ def func1[*A]():
 
 class TypeParamsTypeVarParamSpec(unittest.TestCase):
     def test_paramspec_01(self):
-        code = """def func1[**A: str](): return (A, B, C)"""
-        check_syntax_error(self, code, r"expected '\('")
+        code = """def func1[**A: str](): pass"""
+        check_syntax_error(self, code, "cannot use bound with ParamSpec")
+        code = """def func1[**A: (int, str)](): pass"""
+        check_syntax_error(self, code, "cannot use constraints with ParamSpec")
+        code = """class X[**A: str]: pass"""
+        check_syntax_error(self, code, "cannot use bound with ParamSpec")
+        code = """class X[**A: (int, str)]: pass"""
+        check_syntax_error(self, code, "cannot use constraints with ParamSpec")
+        code = """type X[**A: str] = int"""
+        check_syntax_error(self, code, "cannot use bound with ParamSpec")
+        code = """type X[**A: (int, str)] = int"""
+        check_syntax_error(self, code, "cannot use constraints with ParamSpec")
 
     def test_paramspec_02(self):
         def func1[**A]():
diff --git a/Parser/parser.c b/Parser/parser.c
