Commits on Nov 22, 2024

1. inference: (slightly) improve type stability of capturing closures …

   As an idea to improve type stability for capturing closures, such as in
   #31909, I tried this idea of propagating the closure
   object as a `PartialStruct` whose `fields` include captured variables
   of which types are (partially) known. By performing const-prop on this
   `closure::PartialStruct`, we can achieve a certain level of type
   stability.
   Specifically, I made some modifications to `abstract_eval_new` to allow
   creating `PartialStruct` even for `:new` objects that are
   `!isconcretedispatch` (since `PartialStruct` can now represent abstract
   elements). I also adjusted `const_prop_argument_heuristic` to perform
   aggressive constant propagation using such `closure::PartialStruct`.
   
   As a result, the following code now achieves type stability:
   ```julia
   julia> Base.infer_return_type((Bool,Int,)) do b, y
              x = b ? 1 : missing
              inner = y -> x + y
              return inner(y)
          end
   Any                   # master
   Union{Missing, Int64} # this commit
   ```
   
   However, this alone was not enough to fully resolve #31909.
   The call graph of `map` is extremely complex, and simply applying
   constant propagation everywhere does not achieve the type safety
   requested in the issue.
   
   Nevertheless this commit alone would still improve type stability for
   some cases, so I will go ahead and submit it as a PR.

   

   aviatesk committed Nov 22, 2024
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