INTERNAL ERROR when using typing.ParamSpec

[evhub]

Crash Report

MyPy INTERNAL ERROR when running reproduction code below.

Traceback

break_mypy.py:32: error: An overloaded function outside a stub file must have an implementation  [no-overload-impl]
break_mypy.py:32: 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: 1.6.0
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "mypy\checker.py", line 585, in accept
  File "mypy\nodes.py", line 588, in accept
  File "mypy\checker.py", line 622, in visit_overloaded_func_def
  File "mypy\checker.py", line 652, in _visit_overloaded_func_def
  File "mypy\checker.py", line 762, in check_overlapping_overloads
  File "mypy\checker.py", line 7268, in is_unsafe_overlapping_overload_signatures
  File "mypy\subtypes.py", line 1425, in is_callable_compatible
  File "mypy\subtypes.py", line 1749, in unify_generic_callable
  File "mypy\applytype.py", line 129, in apply_generic_arguments
  File "mypy\expandtype.py", line 71, in expand_type
  File "mypy\types.py", line 1953, in accept
  File "mypy\expandtype.py", line 342, in visit_callable_type
  File "mypy\types.py", line 1877, in copy_modified
  File "mypy\types.py", line 1811, in __init__
AssertionError:
break_mypy.py:32: : note: use --pdb to drop into pdb

To Reproduce

Reproduction code:

from typing import *

_T = TypeVar("_T")
_U = TypeVar("_U")
_V = TypeVar("_V")
_W = TypeVar("_W")
_P = ParamSpec("_P")

@overload
def call(
    _func: Callable[Concatenate[_T, _P], _U],
    _x: _T,
    *args: Any,
    **kwargs: Any,
) -> _U: ...
@overload
def call(
    _func: Callable[Concatenate[_T, _U, _P], _V],
    _x: _T,
    _y: _U,
    *args: Any,
    **kwargs: Any,
) -> _V: ...

Your Environment

• Mypy version used: mypy 1.6.0 (compiled: yes)
• Mypy command-line flags: --show-traceback
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: Python 3.11.4
• Operating system and version: Windows 11

[AlexWaygood]

I confirmed that this still reproduces on master, and with the latest version of the release-1.6 branch. Here's the stack trace on the master branch, using uncompiled mypy:

break_mypy.py:9: error: An overloaded function outside a stub file must have an implementation  [no-overload-impl]
break_mypy.py:9: 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: 1.7.0+dev.72605dc12a89b9c12a502ebfad494b4b9d9b5160
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\alexw\coding\mypy\venv\Scripts\mypy.exe\__main__.py", line 7, in <module>
    sys.exit(console_entry())
  File "C:\Users\alexw\coding\mypy\mypy\__main__.py", line 15, in console_entry
    main()
  File "C:\Users\alexw\coding\mypy\mypy\main.py", line 99, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "C:\Users\alexw\coding\mypy\mypy\main.py", line 178, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "C:\Users\alexw\coding\mypy\mypy\build.py", line 189, in build
    result = _build(
  File "C:\Users\alexw\coding\mypy\mypy\build.py", line 262, in _build
    graph = dispatch(sources, manager, stdout)
  File "C:\Users\alexw\coding\mypy\mypy\build.py", line 2938, in dispatch
    process_graph(graph, manager)
  File "C:\Users\alexw\coding\mypy\mypy\build.py", line 3336, in process_graph
    process_stale_scc(graph, scc, manager)
  File "C:\Users\alexw\coding\mypy\mypy\build.py", line 3437, in process_stale_scc
    graph[id].type_check_first_pass()
  File "C:\Users\alexw\coding\mypy\mypy\build.py", line 2306, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "C:\Users\alexw\coding\mypy\mypy\checker.py", line 477, in check_first_pass
    self.accept(d)
  File "C:\Users\alexw\coding\mypy\mypy\checker.py", line 587, in accept
    stmt.accept(self)
  File "C:\Users\alexw\coding\mypy\mypy\nodes.py", line 575, in accept
    return visitor.visit_overloaded_func_def(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\checker.py", line 624, in visit_overloaded_func_def
    self._visit_overloaded_func_def(defn)
  File "C:\Users\alexw\coding\mypy\mypy\checker.py", line 654, in _visit_overloaded_func_def
    self.check_overlapping_overloads(defn)
  File "C:\Users\alexw\coding\mypy\mypy\checker.py", line 764, in check_overlapping_overloads
    if is_unsafe_overlapping_overload_signatures(sig1, sig2, type_vars):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\checker.py", line 7353, in is_unsafe_overlapping_overload_signatures
    return is_callable_compatible(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\subtypes.py", line 1484, in is_callable_compatible
    unified = unify_generic_callable(
              ^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\subtypes.py", line 1821, in unify_generic_callable
    applied = mypy.applytype.apply_generic_arguments(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\applytype.py", line 129, in apply_generic_arguments
    arg_types=[expand_type(at, id_to_type) for at in callable.arg_types]
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\applytype.py", line 129, in <listcomp>
    arg_types=[expand_type(at, id_to_type) for at in callable.arg_types]
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\expandtype.py", line 71, in expand_type
    return typ.accept(ExpandTypeVisitor(env))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\types.py", line 1954, in accept
    return visitor.visit_callable_type(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\expandtype.py", line 350, in visit_callable_type
    return t.copy_modified(
           ^^^^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\types.py", line 1878, in copy_modified
    modified = CallableType(
               ^^^^^^^^^^^^^
  File "C:\Users\alexw\coding\mypy\mypy\types.py", line 1812, in __init__
    assert not t.prefix.arg_types
AssertionError:

[AlexWaygood]

14418bc3d2c38b9ea776da6029e9d9dc6650b7ea is the first bad commit
commit 14418bc3d2c38b9ea776da6029e9d9dc6650b7ea
Author: Ivan Levkivskyi <levkivskyi@gmail.com>
Date:   Tue Aug 15 20:31:26 2023 +0100

    Polymorphic inference: support for parameter specifications and lambdas (#15837)

14418bc again (cc. @ilevkivskyi)

[ilevkivskyi]

Fix in #16257

[ilevkivskyi]

This is essentially the same story as the other two crashes.

[hauntsaninja]

@evhub Thanks for coconut! Did you encounter the regression on an open source codebase?

[evhub]

@hauntsaninja Thanks! And yep, it showed up in Coconut's type stub for call: https://github.com/evhub/coconut/blob/master/__coconut__/__init__.pyi#L256