Take suggestion from Jukka to have calls to typed dicts always result in exact declared type

See #2621 (comment)

Author: Roy Williams

mypy/checkexpr.py

@@ -246,12 +246,12 @@ def check_typeddict_call_with_kwargs(self, callee: TypedDictType,
         for (item_name, item_expected_type) in callee.items.items():
             item_value = kwargs[item_name]
 
-            item_actual_type = self.chk.check_simple_assignment(
+            self.chk.check_simple_assignment(
                 lvalue_type=item_expected_type, rvalue=item_value, context=item_value,
                 msg=messages.INCOMPATIBLE_TYPES,
                 lvalue_name='TypedDict item "{}"'.format(item_name),
                 rvalue_name='expression')
-            items[item_name] = item_actual_type
+            items[item_name] = item_expected_type
 
         mapping_value_type = join.join_type_list(list(items.values()))
         fallback = self.chk.named_generic_type('typing.Mapping',

mypy/subtypes.py

@@ -211,7 +211,7 @@ def visit_typeddict_type(self, left: TypedDictType) -> bool:
             if not left.names_are_wider_than(right):
                 return False
             for (_, l, r) in left.zip(right):
-                if not is_subtype(l, r, self.check_type_parameter):
+                if not is_equivalent(l, r, self.check_type_parameter):
                     return False
             # (NOTE: Fallbacks don't matter.)
             return True

test-data/unit/check-typeddict.test

@@ -88,6 +88,14 @@ def convert(op: ObjectPoint) -> Point:
     return op  # E: Incompatible return value type (got "ObjectPoint", expected "Point")
 [builtins fixtures/dict.pyi]
 
+[case testCannotConvertTypedDictToSimilarTypedDictWithWiderItemTypes]
+from mypy_extensions import TypedDict
+Point = TypedDict('Point', {'x': int, 'y': int})
+ObjectPoint = TypedDict('ObjectPoint', {'x': object, 'y': object})
+def convert(p: Point) -> ObjectPoint:
+    return p  # E: Incompatible return value type (got "Point", expected "ObjectPoint")
+[builtins fixtures/dict.pyi]
+
 [case testCannotConvertTypedDictToSimilarTypedDictWithIncompatibleItemTypes]
 from mypy_extensions import TypedDict
 Point = TypedDict('Point', {'x': int, 'y': int})
@@ -143,7 +151,6 @@ Point = TypedDict('Point', {'x': int, 'y': int})
 def create_point() -> Point:
     return Point(x=1.2, y=2.5)
 [out]
-main:5: error: Incompatible return value type (got "TypedDict(x=float, y=float)", expected "Point")
 main:5: error: Incompatible types (expression has type "float", TypedDict item "x" has type "int")
 main:5: error: Incompatible types (expression has type "float", TypedDict item "y" has type "int")
 [builtins fixtures/dict.pyi]
@@ -214,9 +221,9 @@ CellWithObject = TypedDict('CellWithObject', {'value': object, 'meta': object})
 c1 = CellWithInt(value=1, meta=42)
 c2 = CellWithObject(value=2, meta='turtle doves')
 joined_cells = [c1, c2]
-reveal_type(c1)             # E: Revealed type is 'TypedDict(value=builtins.int, meta=builtins.int, _fallback=typing.Mapping[builtins.str, builtins.int])'
-reveal_type(c2)             # E: Revealed type is 'TypedDict(value=builtins.int, meta=builtins.str, _fallback=typing.Mapping[builtins.str, builtins.object])'
-reveal_type(joined_cells)   # E: Revealed type is 'builtins.list[TypedDict(value=builtins.int, _fallback=typing.Mapping[builtins.str, builtins.int])]'
+reveal_type(c1)             # E: Revealed type is 'TypedDict(value=builtins.object, meta=builtins.int, _fallback=typing.Mapping[builtins.str, builtins.object])'
+reveal_type(c2)             # E: Revealed type is 'TypedDict(value=builtins.object, meta=builtins.object, _fallback=typing.Mapping[builtins.str, builtins.object])'
+reveal_type(joined_cells)   # E: Revealed type is 'builtins.list[TypedDict(value=builtins.object, _fallback=typing.Mapping[builtins.str, builtins.object])]'
 [builtins fixtures/dict.pyi]
 
 [case testJoinOfDisjointTypedDictsIsEmptyTypedDict]
@@ -227,7 +234,7 @@ d1 = Point(x=0, y=0)
 d2 = Cell(value='pear tree')
 joined_dicts = [d1, d2]
 reveal_type(d1)             # E: Revealed type is 'TypedDict(x=builtins.int, y=builtins.int, _fallback=typing.Mapping[builtins.str, builtins.int])'
-reveal_type(d2)             # E: Revealed type is 'TypedDict(value=builtins.str, _fallback=typing.Mapping[builtins.str, builtins.str])'
+reveal_type(d2)             # E: Revealed type is 'TypedDict(value=builtins.object, _fallback=typing.Mapping[builtins.str, builtins.object])'
 reveal_type(joined_dicts)   # E: Revealed type is 'builtins.list[TypedDict(_fallback=typing.Mapping[builtins.str, builtins.None])]'
 [builtins fixtures/dict.pyi]