False positives for "Attempted to reuse member name in Enum"

[mrossinek]

Bug Report

False positives for Enum member reuse attempts when an Enum has a large number of entries.
I first encountered this issue here

To Reproduce

Unfortunately, I have not yet found a minimal reproducing example.

1. Clone https://gitlab.com/mrossinek/cobib
2. Run mypy --strict src/cobib/config/event.py with mypy -V >= 0.930

Expected Behavior

No errors should occur.

Actual Behavior

I obtain the following errors:

src/cobib/config/event.py:137: error: Attempted to reuse member name "PostAddCommand" in Enum definition "Event"  [misc]
src/cobib/config/event.py:222: error: Attempted to reuse member name "PostImportCommand" in Enum definition "Event"  [misc]
src/cobib/config/event.py:445: error: Attempted to reuse member name "PostBibtexParse" in Enum definition "Event"  [misc]
src/cobib/config/event.py:498: error: Attempted to reuse member name "PostYAMLParse" in Enum definition "Event"  [misc]
src/cobib/config/event.py:551: error: Attempted to reuse member name "PostArxivParse" in Enum definition "Event"  [misc]
src/cobib/config/event.py:578: error: Attempted to reuse member name "PostDOIParse" in Enum definition "Event"  [misc]
src/cobib/config/event.py:605: error: Attempted to reuse member name "PostISBNParse" in Enum definition "Event"  [misc]
src/cobib/config/event.py:632: error: Attempted to reuse member name "PostURLParse" in Enum definition "Event"  [misc]
src/cobib/config/event.py:663: error: Attempted to reuse member name "PostZoteroImport" in Enum definition "Event"  [misc]

Your Environment

• Mypy version used: 0.930 and 0.931
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
python_version = 3.7
show_error_codes = True
warn_return_any = True
warn_unused_configs = True

• Python version used: 3.10.1
• Operating system and version: Arch Linux, 5.15.13-arch1-1 as well as in the python:latest Docker container

More information

I believe that this bug was introduced as part of #11267. It introduced the following line: https://github.com/python/mypy/blob/48d810d/mypy/semanal.py#L2874
Instead, I would expect this line to look more like https://github.com/python/mypy/blob/48d810d/mypy/semanal.py#L453 (i.e. also allow PlaceholderNode objects.

The reason that I believe this to be necessary is open inspecting the runtime data during the offending scenarios. There I was able to extract the following names: SymbolTable object:

SymbolTable(
  PostAddCommand : Mdef/PlaceholderNode (cobib.config.event.Event.PostAddCommand)
  PostArxivParse : Mdef/PlaceholderNode (cobib.config.event.Event.PostArxivParse)
  PostBibtexDump : Mdef/Var (cobib.config.event.Event.PostBibtexDump) : cobib.config.event.Event
  PostBibtexParse : Mdef/PlaceholderNode (cobib.config.event.Event.PostBibtexParse)
  PostDOIParse : Mdef/PlaceholderNode (cobib.config.event.Event.PostDOIParse)
  PostDeleteCommand : Mdef/Var (cobib.config.event.Event.PostDeleteCommand) : cobib.config.event.Event
  PostEditCommand : Mdef/Var (cobib.config.event.Event.PostEditCommand) : cobib.config.event.Event
  PostExportCommand : Mdef/Var (cobib.config.event.Event.PostExportCommand) : cobib.config.event.Event
  PostFileDownload : Mdef/Var (cobib.config.event.Event.PostFileDownload) : cobib.config.event.Event
  PostGitCommit : Mdef/Var (cobib.config.event.Event.PostGitCommit) : cobib.config.event.Event
  PostISBNParse : Mdef/PlaceholderNode (cobib.config.event.Event.PostISBNParse)
  PostImportCommand : Mdef/PlaceholderNode (cobib.config.event.Event.PostImportCommand)
  PostInitCommand : Mdef/Var (cobib.config.event.Event.PostInitCommand) : cobib.config.event.Event
  PostListCommand : Mdef/Var (cobib.config.event.Event.PostListCommand) : cobib.config.event.Event
  PostModifyCommand : Mdef/Var (cobib.config.event.Event.PostModifyCommand) : cobib.config.event.Event
  PostOpenCommand : Mdef/Var (cobib.config.event.Event.PostOpenCommand) : cobib.config.event.Event
  PostRedoCommand : Mdef/Var (cobib.config.event.Event.PostRedoCommand) : cobib.config.event.Event
  PostSearchCommand : Mdef/Var (cobib.config.event.Event.PostSearchCommand) : cobib.config.event.Event
  PostShowCommand : Mdef/Var (cobib.config.event.Event.PostShowCommand) : cobib.config.event.Event
  PostURLParse : Mdef/PlaceholderNode (cobib.config.event.Event.PostURLParse)
  PostUndoCommand : Mdef/Var (cobib.config.event.Event.PostUndoCommand) : cobib.config.event.Event
  PostYAMLDump : Mdef/Var (cobib.config.event.Event.PostYAMLDump) : cobib.config.event.Event
  PostYAMLParse : Mdef/PlaceholderNode (cobib.config.event.Event.PostYAMLParse)
  PostZoteroImport : Mdef/PlaceholderNode (cobib.config.event.Event.PostZoteroImport)
  PreAddCommand : Mdef/Var (cobib.config.event.Event.PreAddCommand) : cobib.config.event.Event
  PreArxivParse : Mdef/Var (cobib.config.event.Event.PreArxivParse) : cobib.config.event.Event
  PreBibtexDump : Mdef/Var (cobib.config.event.Event.PreBibtexDump) : cobib.config.event.Event
  PreBibtexParse : Mdef/Var (cobib.config.event.Event.PreBibtexParse) : cobib.config.event.Event
  PreDOIParse : Mdef/Var (cobib.config.event.Event.PreDOIParse) : cobib.config.event.Event
  PreDeleteCommand : Mdef/Var (cobib.config.event.Event.PreDeleteCommand) : cobib.config.event.Event
  PreEditCommand : Mdef/Var (cobib.config.event.Event.PreEditCommand) : cobib.config.event.Event
  PreExportCommand : Mdef/Var (cobib.config.event.Event.PreExportCommand) : cobib.config.event.Event
  PreFileDownload : Mdef/Var (cobib.config.event.Event.PreFileDownload) : cobib.config.event.Event
  PreGitCommit : Mdef/Var (cobib.config.event.Event.PreGitCommit) : cobib.config.event.Event
  PreISBNParse : Mdef/Var (cobib.config.event.Event.PreISBNParse) : cobib.config.event.Event
  PreImportCommand : Mdef/Var (cobib.config.event.Event.PreImportCommand) : cobib.config.event.Event
  PreInitCommand : Mdef/Var (cobib.config.event.Event.PreInitCommand) : cobib.config.event.Event
  PreListCommand : Mdef/Var (cobib.config.event.Event.PreListCommand) : cobib.config.event.Event
  PreModifyCommand : Mdef/Var (cobib.config.event.Event.PreModifyCommand) : cobib.config.event.Event
  PreOpenCommand : Mdef/Var (cobib.config.event.Event.PreOpenCommand) : cobib.config.event.Event
  PreRedoCommand : Mdef/Var (cobib.config.event.Event.PreRedoCommand) : cobib.config.event.Event
  PreSearchCommand : Mdef/Var (cobib.config.event.Event.PreSearchCommand) : cobib.config.event.Event
  PreShowCommand : Mdef/Var (cobib.config.event.Event.PreShowCommand) : cobib.config.event.Event
  PreURLParse : Mdef/Var (cobib.config.event.Event.PreURLParse) : cobib.config.event.Event
  PreUndoCommand : Mdef/Var (cobib.config.event.Event.PreUndoCommand) : cobib.config.event.Event
  PreYAMLDump : Mdef/Var (cobib.config.event.Event.PreYAMLDump) : cobib.config.event.Event
  PreYAMLParse : Mdef/Var (cobib.config.event.Event.PreYAMLParse) : cobib.config.event.Event
  PreZoteroImport : Mdef/Var (cobib.config.event.Event.PreZoteroImport) : cobib.config.event.Event
  __new__ : Mdef/FuncDef (cobib.config.event.Event.__new__) : def (cls: Any, annotation: Any?) -> Event?
  _annotation_ : Mdef/Var (cobib.config.event.Event._annotation_) : Any
  fire : Mdef/FuncDef (cobib.config.event.Event.fire) : def (self: Any, *args: Any?, **kwargs: Any?) -> Any?
  subscribe : Mdef/FuncDef (cobib.config.event.Event.subscribe) : def (self: Any, function: Callable?) -> Callable?
  validate : Mdef/FuncDef (cobib.config.event.Event.validate) : def (self: Any) -> bool?
)

This is just prior to this error being raised:

Attempted to reuse member name "PostAddCommand" in Enum definition "Event"

The following are the lvalue and names[name] at this specific occurrence.

NameExpr(PostAddCommand) Mdef/PlaceholderNode (cobib.config.event.Event.PostAddCommand)

I am going to open a PR in a second with a suggestion to fix this by also allowing PlaceholderNode objects.