[ruby-core:116309] [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 fxn (Xavier Noria).


@Eregon I feel we need to recenter the discussion to consider `const_source_location` under the current logic that undoes some things if the autoload raises.

To me, there is no doubt `const_source_location` in the code being autoloaded has to return the real location just defined. Because that is coherent with the rest of the local state:

* The lookup finds the constant.
* `defined?(Bar)` returns "constant".
* IMPORTANT: `autoload?(:Bar)` returns `nil`.
* `constants` includes the constant.
* Etc.

So, the runtime is locally consistent, except for `const_source_location`. That one is off compared to the rest.

If an exception is raised, the state of the constant is kind of restored. By the same reasoning, you'd restore `const_source_location` if you will, like `autoload?` goes back to returning the string with the file name again (but you got `nil` before).



----------------------------------------
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-106331

* 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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