Now *CustomType and **CustomType arguments are properly checked

mypy/argmap.py

@@ -1,12 +1,16 @@
 """Utilities for mapping between actual and formal arguments (and their types)."""
 
-from typing import List, Optional, Sequence, Callable, Set
+from typing import TYPE_CHECKING, List, Optional, Sequence, Callable, Set
 
+from mypy.maptype import map_instance_to_supertype
 from mypy.types import (
     Type, Instance, TupleType, AnyType, TypeOfAny, TypedDictType, get_proper_type
 )
 from mypy import nodes
 
+if TYPE_CHECKING:
+    from mypy.infer import ArgumentInferContext
+
 
 def map_actuals_to_formals(actual_kinds: List[nodes.ArgKind],
                            actual_names: Optional[Sequence[Optional[str]]],
@@ -140,11 +144,13 @@ def f(x: int, *args: str) -> None: ...
     needs a separate instance since instances have per-call state.
     """
 
-    def __init__(self) -> None:
+    def __init__(self, context: 'ArgumentInferContext') -> None:
         # Next tuple *args index to use.
         self.tuple_index = 0
         # Keyword arguments in TypedDict **kwargs used.
         self.kwargs_used: Set[str] = set()
+        # Type context for `*` and `**` arg kinds.
+        self.context = context
 
     def expand_actual_type(self,
                            actual_type: Type,
@@ -162,16 +168,21 @@ def expand_actual_type(self,
         This is supposed to be called for each formal, in order. Call multiple times per
         formal if multiple actuals map to a formal.
         """
+        from mypy.subtypes import is_subtype
+
         actual_type = get_proper_type(actual_type)
         if actual_kind == nodes.ARG_STAR:
-            if isinstance(actual_type, Instance):
-                if actual_type.type.fullname == 'builtins.list':
-                    # List *arg.
-                    return actual_type.args[0]
-                elif actual_type.args:
-                    # TODO: Try to map type arguments to Iterable
-                    return actual_type.args[0]
+            if isinstance(actual_type, Instance) and actual_type.args:
+                if is_subtype(actual_type, self.context.iterable_type):
+                    return map_instance_to_supertype(
+                        actual_type,
+                        self.context.iterable_type.type,
+                    ).args[0]
                 else:
+                    # We cannot properly unpack anything other
+                    # than `Iterable` type with `*`.
+                    # Just return `Any`, other parts of code would raise
+                    # a different error for improper use.
                     return AnyType(TypeOfAny.from_error)
             elif isinstance(actual_type, TupleType):
                 # Get the next tuple item of a tuple *arg.
@@ -193,11 +204,17 @@ def expand_actual_type(self,
                     formal_name = (set(actual_type.items.keys()) - self.kwargs_used).pop()
                 self.kwargs_used.add(formal_name)
                 return actual_type.items[formal_name]
-            elif (isinstance(actual_type, Instance)
-                  and (actual_type.type.fullname == 'builtins.dict')):
-                # Dict **arg.
-                # TODO: Handle arbitrary Mapping
-                return actual_type.args[1]
+            elif (
+                isinstance(actual_type, Instance) and
+                len(actual_type.args) > 1 and
+                is_subtype(actual_type, self.context.mapping_type)
+            ):
+                # Only `Mapping` type can be unpacked with `**`.
+                # Other types will produce an error somewhere else.
+                return map_instance_to_supertype(
+                    actual_type,
+                    self.context.mapping_type.type,
+                ).args[1]
             else:
                 return AnyType(TypeOfAny.from_error)
         else:

mypy/checkexpr.py

@@ -45,7 +45,9 @@
 from mypy.maptype import map_instance_to_supertype
 from mypy.messages import MessageBuilder
 from mypy import message_registry
-from mypy.infer import infer_type_arguments, infer_function_type_arguments
+from mypy.infer import (
+    ArgumentInferContext, infer_type_arguments, infer_function_type_arguments,
+)
 from mypy import join
 from mypy.meet import narrow_declared_type, is_overlapping_types
 from mypy.subtypes import is_subtype, is_proper_subtype, is_equivalent, non_method_protocol_members
@@ -1240,6 +1242,7 @@ def infer_function_type_arguments(self, callee_type: CallableType,
 
             inferred_args = infer_function_type_arguments(
                 callee_type, pass1_args, arg_kinds, formal_to_actual,
+                context=self.argument_infer_context(),
                 strict=self.chk.in_checked_function())
 
             if 2 in arg_pass_nums:
@@ -1301,10 +1304,18 @@ def infer_function_type_arguments_pass2(
             callee_type, args, arg_kinds, formal_to_actual)
 
         inferred_args = infer_function_type_arguments(
-            callee_type, arg_types, arg_kinds, formal_to_actual)
+            callee_type, arg_types, arg_kinds, formal_to_actual,
+            context=self.argument_infer_context(),
+        )
 
         return callee_type, inferred_args
 
+    def argument_infer_context(self) -> ArgumentInferContext:
+        return ArgumentInferContext(
+            self.chk.named_type('typing.Mapping'),
+            self.chk.named_type('typing.Iterable'),
+        )
+
     def get_arg_infer_passes(self, arg_types: List[Type],
                              formal_to_actual: List[List[int]],
                              num_actuals: int) -> List[int]:
@@ -1479,7 +1490,7 @@ def check_argument_types(self,
         messages = messages or self.msg
         check_arg = check_arg or self.check_arg
         # Keep track of consumed tuple *arg items.
-        mapper = ArgTypeExpander()
+        mapper = ArgTypeExpander(self.argument_infer_context())
         for i, actuals in enumerate(formal_to_actual):
             for actual in actuals:
                 actual_type = arg_types[actual]

mypy/constraints.py

@@ -1,6 +1,6 @@
 """Type inference constraints."""
 
-from typing import Iterable, List, Optional, Sequence
+from typing import TYPE_CHECKING, Iterable, List, Optional, Sequence
 from typing_extensions import Final
 
 from mypy.types import (
@@ -18,6 +18,9 @@
 from mypy.argmap import ArgTypeExpander
 from mypy.typestate import TypeState
 
+if TYPE_CHECKING:
+    from mypy.infer import ArgumentInferContext
+
 SUBTYPE_OF: Final = 0
 SUPERTYPE_OF: Final = 1
 
@@ -45,14 +48,17 @@ def __repr__(self) -> str:
 
 
 def infer_constraints_for_callable(
-        callee: CallableType, arg_types: Sequence[Optional[Type]], arg_kinds: List[ArgKind],
-        formal_to_actual: List[List[int]]) -> List[Constraint]:
+        callee: CallableType,
+        arg_types: Sequence[Optional[Type]],
+        arg_kinds: List[ArgKind],
+        formal_to_actual: List[List[int]],
+        context: 'ArgumentInferContext') -> List[Constraint]:
     """Infer type variable constraints for a callable and actual arguments.
 
     Return a list of constraints.
     """
     constraints: List[Constraint] = []
-    mapper = ArgTypeExpander()
+    mapper = ArgTypeExpander(context)
 
     for i, actuals in enumerate(formal_to_actual):
         for actual in actuals:

mypy/infer.py

@@ -1,19 +1,34 @@
 """Utilities for type argument inference."""
 
-from typing import List, Optional, Sequence
+from typing import List, Optional, Sequence, NamedTuple
 
 from mypy.constraints import (
     infer_constraints, infer_constraints_for_callable, SUBTYPE_OF, SUPERTYPE_OF
 )
-from mypy.types import Type, TypeVarId, CallableType
+from mypy.types import Type, TypeVarId, CallableType, Instance
 from mypy.nodes import ArgKind
 from mypy.solve import solve_constraints
 
 
+class ArgumentInferContext(NamedTuple):
+    """Type argument inference context.
+
+    We need this because we pass around ``Mapping`` and ``Iterable`` types.
+    These types are only known by ``TypeChecker`` itself.
+    It is required for ``*`` and ``**`` argument inference.
+
+    https://github.com/python/mypy/issues/11144
+    """
+
+    mapping_type: Instance
+    iterable_type: Instance
+
+
 def infer_function_type_arguments(callee_type: CallableType,
                                   arg_types: Sequence[Optional[Type]],
                                   arg_kinds: List[ArgKind],
                                   formal_to_actual: List[List[int]],
+                                  context: ArgumentInferContext,
                                   strict: bool = True) -> List[Optional[Type]]:
     """Infer the type arguments of a generic function.
 
@@ -30,7 +45,7 @@ def infer_function_type_arguments(callee_type: CallableType,
     """
     # Infer constraints.
     constraints = infer_constraints_for_callable(
-        callee_type, arg_types, arg_kinds, formal_to_actual)
+        callee_type, arg_types, arg_kinds, formal_to_actual, context)
 
     # Solve constraints.
     type_vars = callee_type.type_var_ids()

test-data/unit/check-expressions.test

@@ -63,13 +63,7 @@ if str():
     a = 1.1
 class A:
     pass
-[file builtins.py]
-class object:
-    def __init__(self): pass
-class type: pass
-class function: pass
-class float: pass
-class str: pass
+[builtins fixtures/dict.pyi]
 
 [case testComplexLiteral]
 a = 0.0j
@@ -80,13 +74,7 @@ if str():
     a = 1.1j
 class A:
     pass
-[file builtins.py]
-class object:
-    def __init__(self): pass
-class type: pass
-class function: pass
-class complex: pass
-class str: pass
+[builtins fixtures/dict.pyi]
 
 [case testBytesLiteral]
 b, a = None, None # type: (bytes, A)
@@ -99,14 +87,7 @@ if str():
 if str():
     a = b'foo' # E: Incompatible types in assignment (expression has type "bytes", variable has type "A")
 class A: pass
-[file builtins.py]
-class object:
-    def __init__(self): pass
-class type: pass
-class tuple: pass
-class function: pass
-class bytes: pass
-class str: pass
+[builtins fixtures/dict.pyi]
 
 [case testUnicodeLiteralInPython3]
 s = None  # type: str
@@ -1535,15 +1516,7 @@ if str():
 ....a  # E: "ellipsis" has no attribute "a"
 
 class A: pass
-[file builtins.py]
-class object:
-    def __init__(self): pass
-class ellipsis:
-    def __init__(self): pass
-    __class__ = object()
-class type: pass
-class function: pass
-class str: pass
+[builtins fixtures/dict.pyi]
 [out]