Set TypedDicts to always be their declared type as opposed to the type inferred when instantiated (2) (#3099)

[This was implemented originally by @rowillia in #2621. This PR includes
a few test updates.]

* Allow fields on a TypedDict to be subtypes of their declared types.

TypedDicts appear to have explicitly decided not to accept subtypes on fields,
but this behavior is counter intuitive.  This made it so TypedDicts didn't
respect `Any` and caused problems with what should have been ducktype
compatible.  This also brings TypedDicts more in line with other container
types and with how fields on classes behave.

```python
from typing import Dict

def foo() -> Dict[float, object]:
    return {
        1: 32
    }
```

This fixes #2610

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

See #2621 (comment)

Author: JukkaL

mypy/checkexpr.py

@@ -255,12 +255,12 @@ 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',

test-data/unit/check-typeddict.test

@@ -152,7 +152,7 @@ class Point(TypedDict):
     z = int # E: Invalid statement in TypedDict definition; expected "field_name: field_type"
 
 p = Point(x=42, y=1337, z='whatever')
-reveal_type(p)  # E: Revealed type is 'TypedDict(x=builtins.int, y=builtins.int, z=builtins.str, _fallback=typing.Mapping[builtins.str, builtins.object])'
+reveal_type(p)  # E: Revealed type is 'TypedDict(x=builtins.int, y=builtins.int, z=Any, _fallback=typing.Mapping[builtins.str, Any])'
 [builtins fixtures/dict.pyi]
 
 [case testCanCreateTypedDictTypeWithUnderscoreItemName]
@@ -286,6 +286,44 @@ def as_mapping(p: Point) -> Mapping[str, str]:
     return p  # E: Incompatible return value type (got "Point", expected Mapping[str, str])
 [builtins fixtures/dict.pyi]
 
+[case testTypedDictAcceptsIntForFloatDuckTypes]
+from mypy_extensions import TypedDict
+from typing import Any, Mapping
+Point = TypedDict('Point', {'x': float, 'y': float})
+def create_point() -> Point:
+    return Point(x=1, y=2)
+reveal_type(Point(x=1, y=2))  # E: Revealed type is 'TypedDict(x=builtins.float, y=builtins.float, _fallback=typing.Mapping[builtins.str, builtins.float])'
+[builtins fixtures/dict.pyi]
+
+[case testTypedDictDoesNotAcceptsFloatForInt]
+from mypy_extensions import TypedDict
+from typing import Any, Mapping
+Point = TypedDict('Point', {'x': int, 'y': int})
+def create_point() -> Point:
+    return Point(x=1.2, y=2.5)
+[out]
+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]
+
+[case testTypedDictAcceptsAnyType]
+from mypy_extensions import TypedDict
+from typing import Any, Mapping
+Point = TypedDict('Point', {'x': float, 'y': float})
+def create_point(something: Any) -> Point:
+    return Point({
+      'x': something.x,
+      'y': something.y
+    })
+[builtins fixtures/dict.pyi]
+
+[case testTypedDictValueTypeContext]
+from mypy_extensions import TypedDict
+from typing import List
+D = TypedDict('D', {'x': List[int]})
+reveal_type(D(x=[]))  # E: Revealed type is 'TypedDict(x=builtins.list[builtins.int], _fallback=typing.Mapping[builtins.str, builtins.list[builtins.int]])'
+[builtins fixtures/dict.pyi]
+
 -- TODO: Fix mypy stubs so that the following passes in the test suite
 --[case testCanConvertTypedDictToAnySuperclassOfMapping]
 --from mypy_extensions import TypedDict
@@ -341,9 +379,9 @@ 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]
@@ -354,7 +392,7 @@ 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, <uninhabited>])]'
 [builtins fixtures/dict.pyi]