Render star args in error messages properly

Author: Morgan Bartholomew

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Basedmypy Changelog
 
 ## [Unreleased]
+### Fixes
+- Render star args in error messages properly (#551)
 
 ## [2.2.1]
 ### Fixes

mypy/messages.py

@@ -2484,10 +2484,14 @@ def format_callable_args(
                 arg_strings.append(f"{arg_name}: {format(arg_type)} = ...")
                 continue
             elif arg_kind is ARG_STAR:
-                arg_strings.append(f"*{arg_name}: {format(arg_type)}")
+                arg_strings.append(
+                    f"*{arg_name}: {format(arg_type)}" if arg_name else f"*{format(arg_type)}"
+                )
                 continue
             elif arg_kind is ARG_STAR2:
-                arg_strings.append(f"**{arg_name}: {format(arg_type)}")
+                arg_strings.append(
+                    f"**{arg_name}: {format(arg_type)}" if arg_name else f"**{format(arg_type)}"
+                )
                 continue
         if arg_kind == ARG_POS and arg_name is None or verbosity == 0 and arg_kind.is_positional():
             arg_strings.append(format(arg_type))

mypy_self_check.ini

@@ -17,7 +17,7 @@ allow_any_decorated = True
 no_warn_unreachable = True
 implicit_reexport = True
 disallow_redefinition = True
-disable_error_code = truthy-bool, no-untyped-usage, possibly-undefined
+disable_error_code = truthy-bool, no-untyped-usage, possibly-undefined, explicit-override
 bare_literals = True
 show_error_code_links = True
 

test-data/unit/check-based-type-render.test

@@ -79,3 +79,16 @@ b = 1  # E: Incompatible types in assignment (expression has type "int", variabl
 def foo(): ...
 reveal_type(foo)  # N: Revealed type is "def () -> None"
 foo = 1  # E: Incompatible types in assignment (expression has type "int", variable has type "() -> None")  [assignment]
+
+
+[case testRenderErrorStar]
+from typing import Callable, ParamSpec
+
+P = ParamSpec("P")
+
+def f(fn: Callable[P, None]): ...
+f(1)  # E: Argument 1 to "f" has incompatible type "int"; expected "(*Never, **Never) -> None"  [arg-type]
+def f2(*args: int, **kwargs: str): ...
+a = f2
+a = 1  # E: Incompatible types in assignment (expression has type "int", variable has type "(*args: int, **kwargs: str) -> None")  [assignment]
+[builtins fixtures/tuple.pyi]