Using `typing_extension.Unpack` results in INTERNAL ERROR

[stoney95]

Bug Report
I'm trying to use typing_extensions.Unpack in python 3.7.11 to check the annotation of a higher order function. The function with annotation looks like this:

from typing import Tuple, TypeVar
from typing_extension import ParamSpec, Unpack

pipeline(*funcs: Unpack[Tuple[Callable[P, Any], Unpack[Tuple[Callable, ...]], Callable[..., Output]]]) -> Callable[P, Output]:
  ...

I first used the latest published version of mypy (0.982) to do the type checking. this lead to this error:

test_unpack.py:37: error: "Unpack" is not supported yet, use --enable-incomplete-features

Running with the suggested flag --enable-incomplete-features produced another error:

test_unpack.py:37: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
If this issue continues with mypy master, please report a bug at https://github.com/python/mypy/issues
version: 0.982
delete_me.py:37: : note: please use --show-traceback to print a traceback when reporting a bug

So I installed mypy from source. The build version is: 1.0.0+dev.55d0adf17a15ddbd0a8e9fb9d27f848117522a17.
I ran the type check again with the Unpack feature enabled: mypy test_unpack.py --enable-incomplete-feature=Unpack. This resulted in the same error:

test_unpack.py:37: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.0.0+dev.55d0adf17a15ddbd0a8e9fb9d27f848117522a17
Traceback (most recent call last):
  File "/Users/simons/anaconda3/envs/pypely/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/main.py", line 95, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/main.py", line 174, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/build.py", line 194, in build
    sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr, extra_plugins
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/build.py", line 276, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/build.py", line 2903, in dispatch
    process_graph(graph, manager)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/build.py", line 3287, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/build.py", line 3388, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/build.py", line 2309, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 465, in check_first_pass
    self.accept(d)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 573, in accept
    stmt.accept(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/nodes.py", line 822, in accept
    return visitor.visit_func_def(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 938, in visit_func_def
    self._visit_func_def(defn)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 942, in _visit_func_def
    self.check_func_item(defn, name=defn.name)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 1011, in check_func_item
    self.check_func_def(defn, typ, name, allow_empty)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 1208, in check_func_def
    self.accept(item.body)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 573, in accept
    stmt.accept(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/nodes.py", line 1218, in accept
    return visitor.visit_block(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 2569, in visit_block
    self.accept(s)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 573, in accept
    stmt.accept(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/nodes.py", line 1301, in accept
    return visitor.visit_assignment_stmt(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 2617, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checker.py", line 2840, in check_assignment
    rvalue_type = self.expr_checker.accept(rvalue, type_context=type_context)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 4665, in accept
    typ = node.accept(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/nodes.py", line 1838, in accept
    return visitor.visit_call_expr(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 410, in visit_call_expr
    return self.visit_call_expr_inner(e, allow_none_return=allow_none_return)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 531, in visit_call_expr_inner
    callee_type, e, fullname, object_type, member
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 1189, in check_call_expr_with_callee_type
    object_type=object_type,
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 1276, in check_call
    callee, args, arg_kinds, arg_names, callable_name, object_type, context
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 2142, in check_overload_call
    context,
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 2295, in infer_overload_return_type
    object_type=object_type,
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 1272, in check_call
    object_type,
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 1407, in check_callable_call
    callee, args, arg_kinds, formal_to_actual, context
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 1732, in infer_function_type_arguments
    callee_type, args, arg_kinds, formal_to_actual, inferred_args, context
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/checkexpr.py", line 1793, in infer_function_type_arguments_pass2
    context=self.argument_infer_context(),
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/infer.py", line 55, in infer_function_type_arguments
    callee_type, arg_types, arg_kinds, formal_to_actual, context
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 147, in infer_constraints_for_callable
    c = infer_constraints(callee.arg_types[i], actual_type, SUPERTYPE_OF)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 189, in infer_constraints
    return _infer_constraints(template, actual, direction)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 268, in _infer_constraints
    return template.accept(ConstraintBuilderVisitor(actual, direction))
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/types.py", line 1792, in accept
    return visitor.visit_callable_type(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 917, in visit_callable_type
    res.extend(infer_constraints(t, a, neg_op(self.direction)))
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 189, in infer_constraints
    return _infer_constraints(template, actual, direction)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 268, in _infer_constraints
    return template.accept(ConstraintBuilderVisitor(actual, direction))
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/types.py", line 933, in accept
    return visitor.visit_unpack_type(self)
  File "/Users/simons/anaconda3/envs/pypely/lib/python3.7/site-packages/mypy/constraints.py", line 540, in visit_unpack_type
    raise NotImplementedError
NotImplementedError: 
test_unpack.py:37: : note: use --pdb to drop into pdb

To Reproduce

from typing import Any, Callable, Tuple, TypeVar
from typing_extensions import ParamSpec, Unpack
from functools import reduce

P = ParamSpec("P")
CombineFirstOutput = TypeVar("CombineFirstOutput")
CombineSecondOutput = TypeVar("CombineSecondOutput")
Output = TypeVar("Output")

def double(x: int) -> Tuple[int, int]:
    return x*2, x

def add(x: int, y: int) -> int:
    return x + y

def to_string(x: int) -> str:
    return str(x)

def combine(
    func1: Callable[P, CombineFirstOutput], 
    func2: Callable[[CombineFirstOutput], CombineSecondOutput]
) -> Callable[P, CombineSecondOutput]:
    def _inner(*args: P.args, **kwargs: P.kwargs) -> CombineSecondOutput:
        return func2(func1(*args, **kwargs))

    return _inner


def pipeline(*funcs: Unpack[Tuple[Callable[P, Any], Unpack[Tuple[Callable, ...]], Callable[..., Output]]]) -> Callable[P, Output]:
    func = reduce(combine, funcs)

    return func

test2 = pipeline(add, double, add, to_string)

result = test2(3,4)
print(result.upper())

Expected Behavior
A passing type check

Actual Behavior
INTERNAL ERROR occured, which is asking to raise an issue here. As the last error in the verbose traceback is a NotImplementedError I guess the expected behaviour is not implemented yet. This issue is raised as it's stated in the error message.

Your Environment

• Mypy version used: 1.0.0+dev.55d0adf17a15ddbd0a8e9fb9d27f848117522a17 (compiled: no)
• Mypy command-line flags: --enable-incomplete-feature=Unpack
• Mypy configuration options from mypy.ini (and other config files): -
• Python version used: 3.7.11

[ilevkivskyi]

cc @jhance FYI

[hauntsaninja]

Similarly:

from typing import Any, TypeVar
from typing_extensions import Unpack
T = TypeVar("T")

def convert(obj: Any, *to_classes: Unpack[tuple[type[T], ...]]) -> T | None:
    for class_ in to_classes:
        try:
            return class_(...)
        except:
            pass

x = convert(1, int, str)
reveal_type(x)  # int | str | None