Spurious replacing module warning

[nsajko]

julia> module M module M end end
WARNING: replacing module M.
Main.M

julia> M.M
Main.M.M

julia> versioninfo()
Julia Version 1.11.0-DEV.548
Commit b44a95bca72 (2023-09-25 13:40 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 8 × AMD Ryzen 3 5300U with Radeon Graphics
  WORD_SIZE: 64
  LLVM: libLLVM-15.0.7 (ORCJIT, znver2)
  Threads: 1 on 8 virtual cores

module M module M end end results in a false warning message; it appears no module was actually replaced (seeing as the M.M access works fine), contrary to the message.

This may have received some discussion in #23619, but I'm not sure of the relevancy or up-to-dateness of that discussion. I think the discussion in that issue is outdated by the release of Julia 1, because it discusses breaking changes that are now not possible (until v2)?

[nsajko]

Note that this is not a recent regression, v1.6 behaves the same.

[Keno]

The thing that's being replaced is the const self binding inside M:

julia> module M end
Main.M

julia> M.M === M
true

vs

julia> module M module M end end
WARNING: replacing module M.
Main.M

julia> M.M === M
false

This should potentially just be disallowed as the self-binding is assumed to be there by various reflection utilities.