[ruby-core:116364] [Ruby master Bug#20188] `Module#const_source_location` returns wrong information when real constant was defined but autoload is still ongoing

Issue #20188 has been updated by Eregon (Benoit Daloze).


fxn (Xavier Noria) wrote in #note-19:
> The code responsible for loading is the caller, `bar.rb` should work the same no matter how the `require` was issued.

I agree.

> And that is why I am in favor of updating `const_source_location`. And I also agree with you that with the current logic, it should be restored on failure.

Updating seems confusing here because it might imply it affects other threads too.
But it should only affect thread doing the autoload.

>From https://github.com/ruby/ruby/pull/9549#issuecomment-1903680909 these are the desired semantics which also avoids other threads seeing the value change back and forth, and it also means there is no need to "restore":
> To clarify this changes the behavior of const_source_location in the thread doing the autoload (during the autoload) but not for other threads, correct?
> i.e. the (real) constant's location is only visible to other threads after the autoload finished, i.e., at the same time the constant is published to these other threads.


----------------------------------------
Bug #20188: `Module#const_source_location` returns wrong information when real constant was defined but autoload is still ongoing
https://bugs.ruby-lang.org/issues/20188#change-106384

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin23]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
Ref: https://github.com/fxn/zeitwerk/issues/281

`const_source_location` keeps returning the location of the `autoload` call, even after the real constant was defined. It only starts returning the real constant location once the autoload was fully completed.

```ruby
# /tmp/autoload.rb
File.write("/tmp/const.rb", <<~RUBY)
module Const
  LOCATION = Object.const_source_location(:Const)
end
RUBY

autoload :Const, "/tmp/const"

p Const::LOCATION
```

Expected Output:

```ruby
["/tmp/const.rb", 1]
```

Actual Output:

```ruby
["/tmp/autoload.rb", 8]
```

Potential patch: https://github.com/ruby/ruby/pull/9549



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