crash with quoted forward reference #20073
Description
Crash Report
In trying to annotate my project I encountered a mypy INTERNAL ERROR. I'm pretty sure the types are wrong, but thought I should report the crash regardless. I reduced it to a simple reproduction (in the section below).
Traceback
lonniehutchinson@MacBookAir src % mypy --show-traceback mypy_bug.py
mypy_bug.py:4: 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.2c6c3959356674262d9b2c2dc43a33486e807a9c
Traceback (most recent call last):
File "/Users/lonniehutchinson/python3.14_master_mypy/bin/mypy", line 7, in <module>
sys.exit(console_entry())
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/__main__.py", line 15, in console_entry
main()
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/main.py", line 127, in main
res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/main.py", line 211, in run_build
res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/build.py", line 200, in build
result = _build(
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/build.py", line 279, in _build
graph = dispatch(sources, manager, stdout)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/build.py", line 2940, in dispatch
process_graph(graph, manager)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/build.py", line 3340, in process_graph
process_stale_scc(graph, scc, manager)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/build.py", line 3435, in process_stale_scc
mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal_main.py", line 95, in semantic_analysis_for_scc
process_top_levels(graph, scc, patches)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal_main.py", line 222, in process_top_levels
deferred, incomplete, progress = semantic_analyze_target(
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal_main.py", line 399, in semantic_analyze_target
analyzer.refresh_partial(
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal.py", line 658, in refresh_partial
self.refresh_top_level(node)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal.py", line 676, in refresh_top_level
self.accept(d)
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal.py", line 7387, in accept
node.accept(self)
~~~~~~~~~~~^^^^^^
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/nodes.py", line 1445, in accept
return visitor.visit_class_def(self)
~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal.py", line 1776, in visit_class_def
self.analyze_class(defn)
~~~~~~~~~~~~~~~~~~^^^^^^
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal.py", line 1916, in analyze_class
bases, tvar_defs, is_protocol = self.clean_up_bases_and_infer_type_variables(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
defn, bases, context=defn
^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/Users/lonniehutchinson/python3.14_master_mypy/lib/python3.14/site-packages/mypy/semanal.py", line 2223, in clean_up_bases_and_infer_type_variables
assert isinstance(node.node, TypeVarLikeExpr)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError:
mypy_bug.py:4: : note: use --pdb to drop into pdb
To Reproduce
type Tb = object
type Ta[Tb] = 'B[Tb]'
class A[Ta]: ...
class B[Tb](A[Ta]): ...Moving the quoted ref to after B is defined avoids the crash, either still quoted or not quoted. This works:
# this avoids the crash
type Tb = object
class A[Ta]: ...
class B[Tb](A[Ta]): ...
type Ta[Tb] = 'B[Tb]'Your Environment
- Mypy version used: mypy 1.19.0+dev.2c6c3959356674262d9b2c2dc43a33486e807a9c (compiled: no)
- Mypy command-line flags: mypy --show-traceback mypy_bug.py
- Mypy configuration options from
mypy.ini(and other config files): default configuration, no mypy.ini - Python version used: Python 3.14.0 with fresh venv with mypy dev installed using website instructions for using master version from git.
- Operating system and version: macOS 15.6.1 (24G90)