Mypy crash when unpacking typevar tuples (not TypeVarTuple)

Crash Report

Unpacked *args tuple type with TypeVar crashes mypy. Offending source below, crash occurred after introducing *tuple[_S1] as the *args type. This overload is necessary instead of a TypeVarTuple due to the challenge described here

_S1 = TypeVar("_S1", bound=_ScopeType)

@overload
def create_scoped(
    arg1: Arg1,
    arg2: Union[type[TraitsLikeT], TraitsLikeT],
    *scopes: * tuple[_S1 | type[_S1] ],
) -> ScopeContainer[TraitsLikeT, _S1]: ...

Traceback

src/mylib/api/scope.py:238: 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: 1.11.2
Traceback (most recent call last):
  File "mypy/checker.py", line 591, in accept
  File "mypy/nodes.py", line 589, in accept
  File "mypy/checker.py", line 628, in visit_overloaded_func_def
  File "mypy/checker.py", line 658, in _visit_overloaded_func_def
  File "mypy/checker.py", line 825, in check_overlapping_overloads
  File "mypy/subtypes.py", line 1855, in unify_generic_callable
  File "mypy/constraints.py", line 317, in infer_constraints
  File "mypy/constraints.py", line 410, in _infer_constraints
  File "mypy/types.py", line 2004, in accept
  File "mypy/constraints.py", line 1085, in visit_callable_type
  File "mypy/constraints.py", line 1440, in repack_callable_args
AssertionError:

Your Environment

Mypy version used: mypy 1.11.2 (compiled: yes)
Mypy command-line flags:
Mypy configuration options from mypy.ini (and other config files): Only set python_version = 3.11
Python version used: Python 3.11.9
Operating system and version: rhel8

Latest commit on master yields a slightly different backtrace:

version: 1.12.0+dev.0c1036717578b00e35625cc353a538e4eb63bc37
  File ".venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File ".venv/lib/python3.11/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File ".venv/lib/python3.11/site-packages/mypy/main.py", line 102, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File ".venv/lib/python3.11/site-packages/mypy/main.py", line 186, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File ".venv/lib/python3.11/site-packages/mypy/build.py", line 193, in build
    result = _build(
  File ".venv/lib/python3.11/site-packages/mypy/build.py", line 268, in _build
    graph = dispatch(sources, manager, stdout)
  File ".venv/lib/python3.11/site-packages/mypy/build.py", line 2950, in dispatch
    process_graph(graph, manager)
  File ".venv/lib/python3.11/site-packages/mypy/build.py", line 3348, in process_graph
    process_stale_scc(graph, scc, manager)
  File ".venv/lib/python3.11/site-packages/mypy/build.py", line 3449, in process_stale_scc
    graph[id].type_check_first_pass()
  File ".venv/lib/python3.11/site-packages/mypy/build.py", line 2314, in type_check_first_pass
    self.type_checker().check_first_pass()
  File ".venv/lib/python3.11/site-packages/mypy/checker.py", line 483, in check_first_pass
    self.accept(d)
  File ".venv/lib/python3.11/site-packages/mypy/checker.py", line 592, in accept
    stmt.accept(self)
  File ".venv/lib/python3.11/site-packages/mypy/nodes.py", line 589, in accept
    return visitor.visit_overloaded_func_def(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/checker.py", line 629, in visit_overloaded_func_def
    self._visit_overloaded_func_def(defn)
  File ".venv/lib/python3.11/site-packages/mypy/checker.py", line 659, in _visit_overloaded_func_def
    self.check_overlapping_overloads(defn)
  File ".venv/lib/python3.11/site-packages/mypy/checker.py", line 828, in check_overlapping_overloads
    impl: CallableType | None = unify_generic_callable(
                                ^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/subtypes.py", line 1855, in unify_generic_callable
    cs = mypy.constraints.infer_constraints(
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/constraints.py", line 317, in infer_constraints
    return _infer_constraints(template, actual, direction, skip_neg_op)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/constraints.py", line 410, in _infer_constraints
    return template.accept(ConstraintBuilderVisitor(actual, direction, skip_neg_op))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/types.py", line 2004, in accept
    return visitor.visit_callable_type(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/constraints.py", line 1085, in visit_callable_type
    actual_types = repack_callable_args(cactual, tuple_type)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/mypy/constraints.py", line 1440, in repack_callable_args
    assert isinstance(tp.items[0], UnpackType)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pdb shows:

-> assert isinstance(tp.items[0], UnpackType)
(Pdb) p tp.items[0]
Union[_S1`-2, type[_S1`-2]]

Could you please post a more complete (ideally self-contained) example? I am having trouble reproducing this.

Reproduces on the following (playground):

from typing import TypeVar, overload

_T = TypeVar("_T")

@overload
def fn() -> tuple[()]: ...
@overload
def fn(*scopes: *tuple[_T]) -> tuple[_T]: ...
def fn(*scopes: *tuple[_T]) -> tuple[_T]: ...

Fix crash on type inference against non-normal callables (python#18858)

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Mypy crash when unpacking typevar tuples (not TypeVarTuple) #17755

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Mypy crash when unpacking typevar tuples (not TypeVarTuple) #17755

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kdkavanagh commented on Sep 10, 2024

ilevkivskyi commented on Feb 10, 2025

sterliakov commented on Mar 30, 2025

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