Assertion fails in is_overlapping_types() when comparing Unpack TypeVarTuple with default type

[h4l]

Crash Report

mypy reports INTERNAL ERROR (failed assertion) when checking code that calls type(f) is Foo where Foo is a tuple type with Unpacked TypeVarTuple using a default type.

It seems to be related to using the default type of a TypeVarTuple. When the TypeVarTuple's default is not relied on, the internal error does not occur.

Traceback

$ mypy test/test_mypy_is_overlapping_types.py --show-traceback --pdb --strict
test/test_mypy_is_overlapping_types.py:19: 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: 1.14.0+dev.7788c21269006ac2e3ac3bc69e52d68403741e6e
Dropping into pdb
> /home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py(584)is_overlapping_types()
-> assert type(left) != type(right), f"{type(left)} vs {type(right)}"
(Pdb) left
Unpack[builtins.tuple[Union[builtins.str, builtins.int], ...]]
(Pdb) right
Unpack[Pieces`1 = Unpack[builtins.tuple[Union[builtins.str, builtins.int], ...]]]
(Pdb) exit
Traceback (most recent call last):
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/main.py", line 109, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/main.py", line 193, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/build.py", line 194, in build
    result = _build(
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/build.py", line 269, in _build
    graph = dispatch(sources, manager, stdout)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/build.py", line 2940, in dispatch
    process_graph(graph, manager)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/build.py", line 3338, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/build.py", line 3439, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/build.py", line 2309, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 483, in check_first_pass
    self.accept(d)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 592, in accept
    stmt.accept(self)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/nodes.py", line 827, in accept
    return visitor.visit_func_def(self)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 1046, in visit_func_def
    self._visit_func_def(defn)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 1050, in _visit_func_def
    self.check_func_item(defn, name=defn.name)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 1084, in check_func_item
    self.check_func_def(defn, typ, name, allow_empty)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 1360, in check_func_def
    self.accept(item.body)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 592, in accept
    stmt.accept(self)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/nodes.py", line 1277, in accept
    return visitor.visit_block(self)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 2951, in visit_block
    self.accept(s)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 592, in accept
    stmt.accept(self)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/nodes.py", line 1490, in accept
    return visitor.visit_assert_stmt(self)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checker.py", line 4778, in visit_assert_stmt
    self.expr_checker.accept(s.expr)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checkexpr.py", line 5885, in accept
    typ = node.accept(self)
          ^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/nodes.py", line 2156, in accept
    return visitor.visit_comparison_expr(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checkexpr.py", line 3645, in visit_comparison_expr
    if self.dangerous_comparison(left_type, right_type):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/checkexpr.py", line 3790, in dangerous_comparison
    return not is_overlapping_types(left, right, ignore_promotions=False)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 481, in is_overlapping_types
    return _type_object_overlap(left, right) or _type_object_overlap(right, left)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 466, in _type_object_overlap
    return _is_overlapping_types(left.item, right.ret_type)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 306, in _is_overlapping_types
    return is_overlapping_types(
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 570, in is_overlapping_types
    if all(
       ^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 571, in <genexpr>
    _is_overlapping_types(left_arg, right_arg)
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 306, in _is_overlapping_types
    return is_overlapping_types(
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.cache/pypoetry/virtualenvs/denokv-G2ZV__I8-py3.12/lib/python3.12/site-packages/mypy/meet.py", line 584, in is_overlapping_types
    assert type(left) != type(right), f"{type(left)} vs {type(right)}"
           ^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: <class 'mypy.types.UnpackType'> vs <class 'mypy.types.UnpackType'>
test/test_mypy_is_overlapping_types.py:19: : note: use --pdb to drop into pdb

To Reproduce

Run mypy on this code to reproduce (this is what I ran on in the traceback above).

• Changing the Pieces default value to tuple[object ...] stops the error occurring also

from __future__ import annotations

from typing_extensions import TypeVarTuple
from typing_extensions import Unpack

Pieces = TypeVarTuple("Pieces", default=Unpack[tuple[str | int, ...]])


class Foo(tuple[Unpack[Pieces]]):
    pass


def test_mypy_is_overlapping_types_assertion_failure() -> None:
    pieces: tuple[str, int] = ("a", 1)
    f1: Foo[tuple[str, int]] = Foo(pieces)
    assert type(f1) is Foo  # ok

    f2 = Foo(pieces)
    assert type(f2) is Foo  # mypy internal error

Your Environment

• Mypy version used: 1.14.0+dev.7788c21269006ac2e3ac3bc69e52d68403741e6e
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files): None as far as I know, I removed my own config file before running the example above.
• Python version used: Python 3.12.7
• Operating system and version: Debian 12, aarch64 (Linux container)