Type "def func1() -> Unknown | def func2() -> Unknown" is not callable #406

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1. jschear commented on Dec 17, 2025

   

   jschear

   on Dec 17, 2025

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   I'd like to try to contribute a fix here, especially if I can get a pointer to relevant code. I'm guessing this falls under "code flow analysis"?
2. Ahajha commented on Oct 17, 2026

   

   Ahajha

   on Oct 17, 2026

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   @jschear If you still want to help out, take a look at #443 for some inspiration. I think there's 2 paths we can take:

   1. We strip the func1 and func2 pieces and do something similar to my PR, where we special case the unioning of two functions with the same signature. So def func1() -> Unknown | def func2() -> Unknown would become def () -> Unknown (a nameless function type). It may make sense to stack the change on top of my branch.
   2. Special case the union type so that it is callable iff all of its members are callable.

   I could see some arguments for 2, since we don't lose information, but 1 produces a simpler type and the fix should be simpler.

   FYI, the author is quite busy with $dayjob and hasn't been able to look at the repo in a while. I've been maintaining a fork here https://github.com/modular/starpls, happy to cherry pick fixes or if you want to submit a PR there I'm happy to merge it. (I'll be cherry picking my own PR there in the next few days.)
3. jschear commented on Oct 23, 2026

   

   jschear

   on Oct 23, 2026

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   Hi @Ahajha, thanks for the info. I'm no longer at the $dayjob that motivated this issue, so no longer in any real rush to fix it.

   My more complete example looked something like this, where the functions didn't have the exact same type signature, so option 1 wouldn't have fixed my particular issue.

   # in defs.bzl
   def func1(use_foo_feature = False):
       pass
   
   def func2(**kwargs):
       pass
   
   my_func = func1 if True else func2
   
   # in BUILD
   my_func(
     name = "MyTarget",
     use_foo_feature = True,
   )

   But in general it makes sense to me that the union type A | A should be treated as A, so even if that wouldn't have fixed my issue, it might still be a good change? I'll dig in a bit.