Error diagnostics incomplete on generic function redefinition #17791

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1. jolaf

   added

   bugmypy got something wrongmypy got something wrong

   on Sep 19, 2024
2. jolaf

   changed the title [-]Error diagnostics incomplete on function redefinition[/-] [+]Error diagnostics incomplete on generic function redefinition[/+] on Sep 19, 2024
3. brianschubert commented on Sep 20, 2024

   

   brianschubert

   on Sep 20, 2024

   Last edited by brianschubert

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   Relevant snippet here is:

   mypy/mypy/messages.py

   Lines 1501 to 1511 in a646f33

   	def incompatible_conditional_function_def(
   	self, defn: FuncDef, old_type: FunctionLike, new_type: FunctionLike
   	) -> None:
   	self.fail("All conditional function variants must have identical signatures", defn)
   	if isinstance(old_type, (CallableType, Overloaded)) and isinstance(
   	new_type, (CallableType, Overloaded)
   	):
   	self.note("Original:", defn)
   	self.pretty_callable_or_overload(old_type, defn, offset=4)
   	self.note("Redefinition:", defn)
   	self.pretty_callable_or_overload(new_type, defn, offset=4)

   The problem is that the second redefinition message is being suppressed here since it looks like a duplicate of the first definition and allow_dups is set to False in the ErrorInfo.

   A possible fix would be to simply pass allow_dups=True so that the second message is never suppressed:

     self.note("Redefinition:", defn) 
   - self.pretty_callable_or_overload(new_type, defn, offset=4) 
   + self.pretty_callable_or_overload(new_type, defn, offset=4, allow_dups=True) 

   which results in the output:

   main.py:11: error: All conditional function variants must have identical signatures  [misc]
   main.py:11: note: Original:
   main.py:11: note:     def [F] f(a: F) -> F
   main.py:11: note: Redefinition:
   main.py:11: note:     def [F] f(a: F) -> F
   Found 1 error in 1 file (checked 1 source file)
   

   A better fix would be to prevent the rendered definitions from being duplicates to begin with, which may come with the fix to #17792. But I think there would probably be no harm in setting allow_dups=True here anyway, since I can't think of a scenario where we'd want the message after Redefinition: to be suppressed.

   ❤️React with ❤️1Reacted by Vasily Zakharov
4. JelleZijlstra

   added a commit that references this issue on Sep 21, 2024

   Fix TypeVar upper bounds sometimes not being displayed in pretty call…

   ...

   94109aa
5. ilevkivskyi

   closed this as completedin dc42e28on Jun 10, 2025
6. tyralla

   added a commit that references this issue on Jun 10, 2025

   Fix and simplify error de-duplication (python#19247)

   ...

   dc42e28