Show only the missing argument names in error msg (#6795)

rafaelcaricio · ilevkivskyi · commit 7560ee0a868c · 2019-05-07T15:19:51.000-04:00
Fixes #3963
diff --git a/mypy/messages.py b/mypy/messages.py
@@ -644,7 +644,9 @@ def too_few_arguments(self, callee: CallableType, context: Context,
                           argument_names: Optional[Sequence[Optional[str]]]) -> None:
         if (argument_names is not None and not all(k is None for k in argument_names)
                 and len(argument_names) >= 1):
-            diff = [k for k in callee.arg_names if k not in argument_names]
+            num_positional_args = sum(k is None for k in argument_names)
+            arguments_left = callee.arg_names[num_positional_args:]
+            diff = [k for k in arguments_left if k not in argument_names]
             if len(diff) == 1:
                 msg = 'Missing positional argument'
             else:
diff --git a/test-data/unit/check-functions.test b/test-data/unit/check-functions.test
@@ -2328,6 +2328,14 @@ def foo(__b: int, x: int, y: int) -> int: pass
 foo(x=2, y=2)  # E: Missing positional argument
 foo(y=2)  # E: Missing positional arguments
 
+[case testMissingArgumentError]
+def f(a, b, c, d=None) -> None: pass
+f(1, 2, d=3) # E: Missing positional argument "c" in call to "f"
+
+[case testMissingArgumentsError]
+def f(a, b, c, d=None) -> None: pass
+f(1, d=3) # E: Missing positional arguments "b", "c" in call to "f"
+
 [case testReturnTypeLineNumberWithDecorator]
 def dec(f): pass
 
