Still typecheck default parameter, add test case with invalid default parameter

Author: Roy Williams

mypy/checkexpr.py

@@ -341,13 +341,6 @@ def check_call(self, callee: Type, args: List[Expression],
         """
         arg_messages = arg_messages or self.msg
         if isinstance(callee, CallableType):
-            if isinstance(callee, TypedDictGetFunction):
-                if 1 <= len(args) <= 2 and isinstance(args[0], (StrExpr, UnicodeExpr)):
-                    return_type = self.get_typeddict_index_type(callee.typed_dict, args[0])
-                    if len(args) == 1:
-                        return_type = UnionType.make_union([
-                            return_type, NoneTyp()])
-                    return return_type, callee
             if callee.is_concrete_type_obj() and callee.type_object().is_abstract:
                 type = callee.type_object()
                 self.msg.cannot_instantiate_abstract_class(
@@ -369,6 +362,24 @@ def check_call(self, callee: Type, args: List[Expression],
             arg_types = self.infer_arg_types_in_context2(
                 callee, args, arg_kinds, formal_to_actual)
 
+            if isinstance(callee, TypedDictGetFunction):
+                if 1 <= len(args) <= 2 and isinstance(args[0], (StrExpr, UnicodeExpr)):
+                    return_type = self.get_typeddict_index_type(callee.typed_dict, args[0])
+                    if len(args) == 1:
+                        return_type = UnionType.make_union([
+                            return_type, NoneTyp()])
+                    else:
+                        # Explicitly set the return type to be a the TypedDict in cases where the
+                        # call site is of the form `x.get('key', {})` and x['key'] is another
+                        # TypedDict.  This special case allows for chaining of `get` methods when
+                        # accessing elements deep within nested dictionaries in a safe and
+                        # concise way without having to set up exception handlers.
+                        if not (isinstance(return_type, TypedDictType) and
+                                is_subtype(arg_types[1], self.named_type('typing.Mapping'))):
+                            return_type = UnionType.make_simplified_union(
+                                [return_type, arg_types[1]])
+                    return return_type, callee
+
             self.check_argument_count(callee, arg_types, arg_kinds,
                                       arg_names, formal_to_actual, context, self.msg)
 

test-data/unit/check-typeddict.test

@@ -438,6 +438,15 @@ p = TaggedPoint(type='2d', x=42, y=1337)
 reveal_type(p.get('type'))  # E: Revealed type is 'Union[builtins.str, builtins.None]'
 reveal_type(p.get('x'))     # E: Revealed type is 'Union[builtins.int, builtins.None]'
 reveal_type(p.get('y', 0))     # E: Revealed type is 'builtins.int'
+reveal_type(p.get('y', 'hello'))     # E: Revealed type is 'Union[builtins.int, builtins.str]'
+reveal_type(p.get('y', {}))     # E: Revealed type is 'Union[builtins.int, builtins.dict[builtins.None, builtins.None]]'
+[builtins fixtures/dict.pyi]
+
+[case testDefaultParameterStillTypeChecked]
+from mypy_extensions import TypedDict
+TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': int, 'y': int})
+p = TaggedPoint(type='2d', x=42, y=1337)
+p.get('x', 1 + 'y')     # E: Unsupported operand types for + ("int" and "str")
 [builtins fixtures/dict.pyi]
 
 [case testCannotGetMethodWithInvalidStringLiteralKey]
@@ -455,14 +464,22 @@ key = 'type'
 reveal_type(p.get(key))  # E: Revealed type is 'builtins.object*'
 [builtins fixtures/dict.pyi]
 
-[case testChainedGetMethodWithFallback]
+[case testChainedGetMethodWithDictFallback]
 from mypy_extensions import TypedDict
 TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': int, 'y': int})
 PointSet = TypedDict('PointSet', {'first_point': TaggedPoint})
 p = PointSet(first_point=TaggedPoint(type='2d', x=42, y=1337))
 reveal_type(p.get('first_point', {}).get('x', 0))  # E: Revealed type is 'builtins.int'
 [builtins fixtures/dict.pyi]
 
+[case testChainedGetMethodWithNonDictFallback]
+from mypy_extensions import TypedDict
+TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': int, 'y': int})
+PointSet = TypedDict('PointSet', {'first_point': TaggedPoint})
+p = PointSet(first_point=TaggedPoint(type='2d', x=42, y=1337))
+p.get('first_point', 32).get('x', 0)  # E: Some element of union has no attribute "get"
+[builtins fixtures/dict.pyi]
+
 [case testDictGetMethodStillCallable]
 from typing import Callable
 from mypy_extensions import TypedDict