Commits on Jun 8, 2024

1. Don't let setglobal! implicitly create bindings …

   PR #44231 (part of Julia 1.9) introduced the ability to modify globals with `Mod.sym = val` syntax.
   However, the intention of this syntax was always to modify *existing* globals in other modules.
   Unfortunately, as implemented, it also implicitly creates new bindings in the other module, even
   if the binding was not previously declared. This was not intended, but it's a bit of a syntax corner
   case, so nobody caught it at the time.
   
   After some extensive discussions and taking into account the near future direction we want to go
   with bindings (#54654 for both), the consensus was reached that we should try to undo the implicit
   creation of bindings (but not the ability to assign the *value* of globals in other modules).
   Note that this was always an error until Julia 1.9, so hopefully it hasn't crept into too many
   packages yet. We'll see what pkgeval says. If use is extensive, we may want to consider a softer
   removal strategy.
   
   Across base and stdlib, there's two cases affected by this change:
   1. A left over debug statement in `precompile` that wanted to assign a new variable in Base for debugging. Removed in this PR.
   2. Distributed wanting to create new bindings. This is a legimitate use case for wanting to
      create bindings in other modules. This is fixed in JuliaLang/Distributed.jl#102.
   
   As noted in that PR, the recommended replacement where implicit binding creation is desired is:
   ```
   Core.eval(mod, Expr(:global, sym))
   invokelatest(setglobal!, mod, sym, val)
   ```
   
   The `invokelatest` is not presently required, but may be needed by #54654, so it's included
   in the recommendation now.
   
   Fixes #54607

   

   Keno committed Jun 8, 2024
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