AssertionError when using reveal_type on a class-bound ParamSpec. #19839
Description
Crash Report
The following code triggers an AssertionError internally in mypy:
from collections.abc import Callable
from typing import reveal_type
class Sneaky[**P]:
def __init__(self, fn: Callable[P, object], *args: P.args, **kwargs: P.kwargs) -> None:
self.args = args
self.kwargs = kwargs
def identity(x: int) -> int:
return x
reveal_type(Sneaky(identity, 1).args)Traceback
Traceback (most recent call last):
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/__main__.py", line 37, in <module>
console_entry()
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/__main__.py", line 15, in console_entry
main()
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/main.py", line 127, in main
res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/main.py", line 211, in run_build
res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 197, in build
result = _build(
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 273, in _build
graph = dispatch(sources, manager, stdout)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 2970, in dispatch
process_graph(graph, manager)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 3403, in process_graph
process_stale_scc(graph, scc, manager)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 3504, in process_stale_scc
graph[id].type_check_first_pass()
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/build.py", line 2344, in type_check_first_pass
self.type_checker().check_first_pass()
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 524, in check_first_pass
self.accept(d)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 635, in accept
stmt.accept(self)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 1562, in accept
return visitor.visit_expression_stmt(self)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checker.py", line 4842, in visit_expression_stmt
expr_type = self.expr_checker.accept(s.expr, allow_none_return=True, always_allow_any=True)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 6020, in accept
typ = self.visit_call_expr(node, allow_none_return=True)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 493, in visit_call_expr
return self.accept(e.analyzed, self.type_context[-1])
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 6048, in accept
typ = node.accept(self)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 2520, in accept
return visitor.visit_reveal_expr(self)
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 4723, in visit_reveal_expr
revealed_type = self.accept(
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 6048, in accept
typ = node.accept(self)
^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/nodes.py", line 2175, in accept
return visitor.visit_member_expr(self)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 3315, in visit_member_expr
result = self.analyze_ordinary_member_access(e, is_lvalue)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkexpr.py", line 3345, in analyze_ordinary_member_access
member_type = analyze_member_access(
^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkmember.py", line 227, in analyze_member_access
result = _analyze_member_access(name, typ, mx, override_info)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkmember.py", line 244, in _analyze_member_access
return analyze_instance_member_access(name, typ, mx, override_info)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkmember.py", line 386, in analyze_instance_member_access
return analyze_member_var_access(name, typ, info, mx)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkmember.py", line 570, in analyze_member_var_access
return analyze_var(name, v, itype, mx, implicit=implicit, is_trivial_self=is_trivial_self)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkmember.py", line 888, in analyze_var
result = expand_without_binding(typ, var, itype, original_itype, mx)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/checkmember.py", line 955, in expand_without_binding
expanded = expand_type_by_instance(typ, itype)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/expandtype.py", line 115, in expand_type_by_instance
return expand_type(typ, variables)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/expandtype.py", line 70, in expand_type
return typ.accept(ExpandTypeVisitor(env))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/types.py", line 823, in accept
return visitor.visit_param_spec(self)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/layers/google.python.pip/pip/lib/python3.12/site-packages/mypy/expandtype.py", line 273, in visit_param_spec
assert t.flavor == ParamSpecFlavor.BARE
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError:
main.py:14: 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: 1.19.0+dev.9ae3e9aa160c11b99960f12eef111e4a3197b7d3
main.py:14: : note: use --pdb to drop into pdbTo Reproduce
The above code should be sufficient; here's a mypy-play link for convenience.
AFAICT it's reproducible across all versions of mypy that support PEP 695 generics, including versions that require --enable-incomplete-feature=NewGenericSyntax (1.11.0 and up). Something of note is that mypy doesn't trigger the assertion if we define the ParamSpec explicitly with P = ParamSpec("P") (mypy-play link).