From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2025-02-17T15:45:15+00:00
Subject: [ruby-core:121089] [Ruby master Misc#21035] Clarify or redefine Module#autoload? and Module#const_defined?

Issue #21035 has been updated by Eregon (Benoit Daloze).


Right, I think that would be a good question to ask for the next dev meeting, can you add an item there?

I posted my guess above but I'm not sure that's the reason and I don't know the initial rationale for making these predicates behave differently during an ongoing autoload (for the constant being autoloaded).

Regarding `require "a_feature_associated_with_an_autoload"` basically behaving the same as triggering the autoload via accessing the constant I think that's something which is ready to be documented because the intention seems clear.

----------------------------------------
Misc #21035: Clarify or redefine Module#autoload? and Module#const_defined?
https://bugs.ruby-lang.org/issues/21035#change-112009

* Author: fxn (Xavier Noria)
* Status: Closed
----------------------------------------
The documentation for `Module#autoload?` says:

> Returns filename to be loaded if name is registered as autoload in the namespace of mod or one of its ancestors.

As a user, if I declare an autoload, I expect this API:

```ruby
module M
  autoload :Foo, 'foo'

  constants            # => [:Foo]
  const_defined?(:Foo) # => true
  autoload?(:Foo)      # => 'foo'
end
```

That it is indeed how it generally works. Even if the autoload path does not exist. But there is an edge case.

While `constants` does include always `:Foo` as far as I can tell, the return value of `const_defined?` and `autoload?` depends on the stack of features being loaded: The autoload path is resolved and if seen to be in the stack of features being loaded, the predicates return `false` and `nil`, respectively. Do you think that is intuitive?

I find that logic totally unexpected. I just defined an autoload, therefore, I think it would be natural for `autoload?` to return what I just configured. Why should `const_defined?` return nothing but `true`? And why is it not consistent with `constants`?

To me, it would make more sense that in the previous example `const_defined?` returns `true`, and `autoload?` returns `foo` unconditionally (and instantly, nowadays it takes a relative long time due to the lookup).

Now, if the autoload is triggered in a lookup **then** I would expect `Kernel#require` logic to apply. But not when calling some simple predicates.

Please, note that the present behavior is not documented, so on paper the change would not be backwards incompatible.

If, on the other side, it is preferred to keep the behavior as it is, I guess it should be documented with precision (accounting for symlinks, relative paths in `$LOAD_PATH`, etc.)




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