[ruby-core:116476] [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 byroot (Jean Boussier).


> If a fiber does a non-blocking operation while the file is being loaded, and that was part of an autoload or require, what can we assume about that situation?

I don't think it's anything particular to `autoload`.

`autoload` simply add an implicit Mutex around the initial constant access, and as you noted, fibers being cooperative, a mistake can lead to a deadlock. But it's not specific to `autoload`, any other mutex would cause the same issue, and I can't think of anything `autoload` could or should do here.

----------------------------------------
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-106496

* 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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