Crash if a class is generic over a PEP-695 parameter that has the same name as an old-style TypeVar that is also in scope and the old-style TypeVar has a bound which uses an unquoted forward reference

[AlexWaygood]

Crash Report

This feels quite specific, but I think it may come up a surprising amount as more and more people use codemods to try to auto-upgrade their code to use PEP 695 in the coming years! Mypy crashes on this snippet:

from typing import TypeVar

T = TypeVar("T", bound=Foo)

class Foo: ...
class Bar[T]: ...

The following things must all be true for the crash to occur:

• The global-scope TypeVar must have the same name as the type parameter used for Bar
• The global-scope TypeVar must have a bound= argument that uses a forward reference
• The forward reference in the global-scope TypeVar's bound must be unquoted. (For .py files, you generally need to quote all forward references, but this is not true for stubs.)

Traceback

% mypy foo.py --python-version=3.12 --show-traceback
foo.py:6: 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: 1.15.0+dev.58de753b6b76227ff726e9ce1888cfc24c7ba44b
Traceback (most recent call last):
  File "/Users/alexw/dev/typeshed/.venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/alexw/dev/mypy/mypy/__main__.py", line 15, in console_entry
    main()
  File "/Users/alexw/dev/mypy/mypy/main.py", line 119, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/alexw/dev/mypy/mypy/main.py", line 203, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/alexw/dev/mypy/mypy/build.py", line 191, in build
    result = _build(
  File "/Users/alexw/dev/mypy/mypy/build.py", line 267, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/alexw/dev/mypy/mypy/build.py", line 2937, in dispatch
    process_graph(graph, manager)
  File "/Users/alexw/dev/mypy/mypy/build.py", line 3335, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/alexw/dev/mypy/mypy/build.py", line 3430, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/Users/alexw/dev/mypy/mypy/semanal_main.py", line 93, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "/Users/alexw/dev/mypy/mypy/semanal_main.py", line 220, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(
  File "/Users/alexw/dev/mypy/mypy/semanal_main.py", line 351, in semantic_analyze_target
    analyzer.refresh_partial(
  File "/Users/alexw/dev/mypy/mypy/semanal.py", line 646, in refresh_partial
    self.refresh_top_level(node)
  File "/Users/alexw/dev/mypy/mypy/semanal.py", line 657, in refresh_top_level
    self.accept(d)
  File "/Users/alexw/dev/mypy/mypy/semanal.py", line 7241, in accept
    node.accept(self)
    ~~~~~~~~~~~^^^^^^
  File "/Users/alexw/dev/mypy/mypy/nodes.py", line 1177, in accept
    return visitor.visit_class_def(self)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/alexw/dev/mypy/mypy/semanal.py", line 1728, in visit_class_def
    self.analyze_class(defn)
    ~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/alexw/dev/mypy/mypy/semanal.py", line 1869, in analyze_class
    bases, tvar_defs, is_protocol = self.clean_up_bases_and_infer_type_variables(
                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        defn, bases, context=defn
        ^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/Users/alexw/dev/mypy/mypy/semanal.py", line 2174, in clean_up_bases_and_infer_type_variables
    assert isinstance(node.node, TypeVarLikeExpr)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError:

To Reproduce

Paste the above snippet into a foo.py file and run mypy --python-version=3.12 foo.py --show-traceback

Your Environment

• Mypy version used: 1.15.0+dev.58de753b6b76227ff726e9ce1888cfc24c7ba44b
• Mypy command-line flags: --python-version=3.12 --show-traceback
• Python version used: 3.13.1

[AlexWaygood]

(Feel free to retitle the issue if you can think of something snappier...)