fix #16935 fix type of tuple[X,Y] expression (#17235)

implement the mypy/checkexpr.py TODO: Specialize the callable for the
type arguments
... so e.g. reveal_type(tuple[int, int]) gives expected
def (p0: tuple[builtins.int, builtins.int]) -> tuple[builtins.int,
builtins.int]

... rather than
def [_T_co] (typing.Iterable[_T_co`1] =) -> builtins.tuple[_T_co`1, ...]

Fixes #16935

mypy/checkexpr.py

@@ -4836,8 +4836,21 @@ def apply_type_arguments_to_callable(
                 len(args) < min_arg_count or len(args) > len(tp.variables)
             ) and not has_type_var_tuple:
                 if tp.is_type_obj() and tp.type_object().fullname == "builtins.tuple":
-                    # TODO: Specialize the callable for the type arguments
-                    return tp
+                    # e.g. expression tuple[X, Y]
+                    # - want the type of the expression i.e. a function with that as its return type
+                    # - tp is type of tuple (note it won't have params as we are only called
+                    #   with generic callable type)
+                    # - tuple[X, Y]() takes a single arg that is a tuple containing an X and a Y
+                    return CallableType(
+                        [TupleType(list(args), self.chk.named_type("tuple"))],
+                        [ARG_POS],
+                        [None],
+                        TupleType(list(args), self.chk.named_type("tuple")),
+                        tp.fallback,
+                        name="tuple",
+                        definition=tp.definition,
+                        bound_args=tp.bound_args,
+                    )
                 self.msg.incompatible_type_application(
                     min_arg_count, len(tp.variables), len(args), ctx
                 )

test-data/unit/check-type-object-type-inference.test

@@ -0,0 +1,41 @@
+[case testInferTupleType]
+# flags: --python-version 3.9
+from typing import TypeVar, Generic, Type
+from abc import abstractmethod
+
+T = TypeVar('T')
+class E(Generic[T]):
+    @abstractmethod
+    def e(self, t: T) -> str:
+        ...
+
+class F:
+    @abstractmethod
+    def f(self, tp: Type[T]) -> E[T]:
+        ...
+
+def g(f: F):
+    f.f(int).e(7)
+    f.f(tuple[int,str])
+    f.f(tuple[int,str]).e('x')  # E: Argument 1 to "e" of "E" has incompatible type "str"; expected "Tuple[int, str]"
+    f.f(tuple[int,str]).e( (7,8) )  # E: Argument 1 to "e" of "E" has incompatible type "Tuple[int, int]"; expected "Tuple[int, str]"
+    f.f(tuple[int,str]).e( (7,'x') )  # OK
+    reveal_type(f.f(tuple[int,str]).e)  # N: Revealed type is "def (t: Tuple[builtins.int, builtins.str]) -> builtins.str"
+
+def h(f: F):
+    f.f(int).e(7)
+    f.f(tuple)
+    f.f(tuple).e('y') # E: Argument 1 to "e" of "E" has incompatible type "str"; expected "Tuple[Any, ...]"
+    f.f(tuple).e( (8,'y') )  # OK
+    reveal_type(f.f(tuple).e)  # N: Revealed type is "def (t: builtins.tuple[Any, ...]) -> builtins.str"
+
+def i(f: F):
+    f.f(tuple[int,tuple[int,str]])
+    f.f(tuple[int,tuple[int,str]]).e('z')  # E: Argument 1 to "e" of "E" has incompatible type "str"; expected "Tuple[int, Tuple[int, str]]"
+    f.f(tuple[int,tuple[int,str]]).e( (8,9) )  # E: Argument 1 to "e" of "E" has incompatible type "Tuple[int, int]"; expected "Tuple[int, Tuple[int, str]]"
+    f.f(tuple[int,tuple[int,str]]).e( (17, (28, 29)) )  # E: Argument 1 to "e" of "E" has incompatible type "Tuple[int, Tuple[int, int]]"; expected "Tuple[int, Tuple[int, str]]"
+    f.f(tuple[int,tuple[int,str]]).e( (27,(28,'z')) )  # OK
+    reveal_type(f.f(tuple[int,tuple[int,str]]).e)  # N: Revealed type is "def (t: Tuple[builtins.int, Tuple[builtins.int, builtins.str]]) -> builtins.str"
+
+x = tuple[int,str][str]  # E: The type "Type[Tuple[Any, ...]]" is not generic and not indexable
+[builtins fixtures/tuple.pyi]

test-data/unit/pythoneval.test

@@ -1834,7 +1834,6 @@ RHSAlias3: type = tuple[int, ...]
 WrongTypeElement = str | tuple[float, 1]  # Error
 WrongEllipsis = tuple[float, float, ...] | str  # Error
 
-# TODO: This should produce a fixed-length tuple
 reveal_type(tuple[int, str]((1, "x")))
 [out]
 _testTupleWithDifferentArgsPy310.py:15: note: Revealed type is "Union[builtins.str, Tuple[builtins.float, builtins.float, builtins.str]]"
@@ -1845,7 +1844,7 @@ _testTupleWithDifferentArgsPy310.py:19: note: Revealed type is "builtins.tuple[b
 _testTupleWithDifferentArgsPy310.py:20: note: Revealed type is "builtins.list[Tuple[builtins.int, builtins.str]]"
 _testTupleWithDifferentArgsPy310.py:26: error: Invalid type: try using Literal[1] instead?
 _testTupleWithDifferentArgsPy310.py:27: error: Unexpected "..."
-_testTupleWithDifferentArgsPy310.py:30: note: Revealed type is "builtins.tuple[builtins.object, ...]"
+_testTupleWithDifferentArgsPy310.py:29: note: Revealed type is "Tuple[builtins.int, builtins.str]"
 
 [case testEnumIterMetaInference]
 import socket