Correct missing positional args when optional args present (python#7547)

PattenR · msullivan · commit bd0864e158dc · 2019-09-21T13:24:46.000-07:00
Fixes python#7527
diff --git a/mypy/messages.py b/mypy/messages.py
@@ -523,7 +523,7 @@ def too_few_arguments(self, callee: CallableType, context: Context,
         if (argument_names is not None and not all(k is None for k in argument_names)
                 and len(argument_names) >= 1):
             num_positional_args = sum(k is None for k in argument_names)
-            arguments_left = callee.arg_names[num_positional_args:]
+            arguments_left = callee.arg_names[num_positional_args:callee.min_args]
             diff = [k for k in arguments_left if k not in argument_names]
             if len(diff) == 1:
                 msg = 'Missing positional argument'
diff --git a/test-data/unit/check-functions.test b/test-data/unit/check-functions.test
@@ -2333,6 +2333,10 @@ foo(y=2)  # E: Missing positional arguments
 def f(a, b, c, d=None) -> None: pass
 f(1, 2, d=3) # E: Missing positional argument "c" in call to "f"
 
+[case testMissingArgumentErrorMoreThanOneOptional]
+def f(a: int, b=None, c=None) -> None: pass
+f(b=4) # E: Missing positional argument "a" 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"
