Preserve the name of first argument in methods when serializing

mypy/messages.py

@@ -1254,6 +1254,13 @@ def [T <: int] f(self, x: int, y: T) -> None
                     s = ', ' + s
                 s = definition_args[0] + s
             s = '{}({})'.format(tp.definition.name(), s)
+        elif tp.name:
+            first_arg = tp.def_extras.get('first_arg')
+            if first_arg:
+                if s:
+                    s = ', ' + s
+                s = first_arg + s
+            s = '{}({})'.format(tp.name.split()[0], s)  # skip "of Class" part
         else:
             s = '({})'.format(s)
 

mypy/types.py

@@ -13,6 +13,7 @@
 from mypy import experiments
 from mypy.nodes import (
     INVARIANT, SymbolNode, ARG_POS, ARG_OPT, ARG_STAR, ARG_STAR2, ARG_NAMED, ARG_NAMED_OPT,
+    FuncDef
 )
 from mypy.sharedparse import argument_elide_name
 from mypy.util import IdMapper
@@ -676,6 +677,8 @@ class CallableType(FunctionLike):
                                     # instantiation?
                  'bound_args',  # Bound type args, mostly unused but may be useful for
                                 # tools that consume mypy ASTs
+                 'def_extras',  # Information about original definition we want to serialize.
+                                # This is used for more detailed error messages.
                  )
 
     def __init__(self,
@@ -695,6 +698,7 @@ def __init__(self,
                  special_sig: Optional[str] = None,
                  from_type_type: bool = False,
                  bound_args: Sequence[Optional[Type]] = (),
+                 def_extras: Optional[Dict[str, Any]] = None,
                  ) -> None:
         super().__init__(line, column)
         assert len(arg_types) == len(arg_kinds) == len(arg_names)
@@ -721,6 +725,18 @@ def __init__(self,
         if not bound_args:
             bound_args = ()
         self.bound_args = bound_args
+        if def_extras:
+            self.def_extras = def_extras
+        elif isinstance(definition, FuncDef):
+            # This information would be lost if we don't have definition
+            # after serialization, but it is useful in error messages.
+            # TODO: decide how to add more info here (file, line, column)
+            # without changing interface hash.
+            self.def_extras = {'first_arg': definition.arg_names[0]
+                               if definition.arg_names and definition.info and
+                               not definition.is_static else None}
+        else:
+            self.def_extras = {}
 
     def copy_modified(self,
                       arg_types: List[Type] = _dummy,
@@ -736,7 +752,8 @@ def copy_modified(self,
                       is_ellipsis_args: bool = _dummy,
                       special_sig: Optional[str] = _dummy,
                       from_type_type: bool = _dummy,
-                      bound_args: List[Optional[Type]] = _dummy) -> 'CallableType':
+                      bound_args: List[Optional[Type]] = _dummy,
+                      def_extras: Dict[str, Any] = _dummy) -> 'CallableType':
         return CallableType(
             arg_types=arg_types if arg_types is not _dummy else self.arg_types,
             arg_kinds=arg_kinds if arg_kinds is not _dummy else self.arg_kinds,
@@ -755,6 +772,7 @@ def copy_modified(self,
             special_sig=special_sig if special_sig is not _dummy else self.special_sig,
             from_type_type=from_type_type if from_type_type is not _dummy else self.from_type_type,
             bound_args=bound_args if bound_args is not _dummy else self.bound_args,
+            def_extras=def_extras if def_extras is not _dummy else dict(self.def_extras),
         )
 
     def is_type_obj(self) -> bool:
@@ -907,6 +925,7 @@ def serialize(self) -> JsonDict:
                 'is_classmethod_class': self.is_classmethod_class,
                 'bound_args': [(None if t is None else t.serialize())
                                for t in self.bound_args],
+                'def_extras': dict(self.def_extras),
                 }
 
     @classmethod
@@ -925,6 +944,7 @@ def deserialize(cls, data: JsonDict) -> 'CallableType':
                             is_classmethod_class=data['is_classmethod_class'],
                             bound_args=[(None if t is None else deserialize_type(t))
                                         for t in data['bound_args']],
+                            def_extras=data['def_extras']
                             )
 
 

test-data/unit/check-incremental.test

@@ -4378,3 +4378,35 @@ from d import k
 [file t.py.2]
 from d import k
 # dummy change
+
+[case testCachedBadProtocolNote]
+import b
+[file a.py]
+from mypy_extensions import TypedDict
+Point = TypedDict('Point', {'x': int, 'y': int})
+[file b.py]
+from typing import Iterable
+from a import Point
+p: Point
+it: Iterable[int] = p
+[file b.py.2]
+from typing import Iterable
+from a import Point
+p: Point
+it: Iterable[int] = p  # change
+[typing fixtures/typing-full.pyi]
+[builtins fixtures/dict.pyi]
+[out]
+tmp/b.py:4: error: Incompatible types in assignment (expression has type "Point", variable has type "Iterable[int]")
+tmp/b.py:4: note: Following member(s) of "Point" have conflicts:
+tmp/b.py:4: note:     Expected:
+tmp/b.py:4: note:         def __iter__(self) -> Iterator[int]
+tmp/b.py:4: note:     Got:
+tmp/b.py:4: note:         def __iter__(self) -> Iterator[str]
+[out2]
+tmp/b.py:4: error: Incompatible types in assignment (expression has type "Point", variable has type "Iterable[int]")
+tmp/b.py:4: note: Following member(s) of "Point" have conflicts:
+tmp/b.py:4: note:     Expected:
+tmp/b.py:4: note:         def __iter__(self) -> Iterator[int]
+tmp/b.py:4: note:     Got:
+tmp/b.py:4: note:         def __iter__(self) -> Iterator[str]