From: "mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date: 2025-02-14T00:59:02+00:00
Subject: [ruby-core:120994] [Ruby master Misc#21035] Clarify or redefine Module#autoload? and Module#const_defined?

Issue #21035 has been updated by mame (Yusuke Endoh).


I'm not going to argue with the definition of the word "circular require", but I don't think that code is valid anyway. It does not use autoload correctly. The circular require/autoload should be resolved.

> In some logic while scanning the file system, Zeitwerk needs to know if a given constant is already set, either exists for real or has an autoload, because in that case it should decline managing the corresponding file, and move on with the scanning. Due to this logic, I need to manually test and register those edge cases because the API is insufficient.

This one is difficult to understand. It would be nice if you could write a demo with short valid code.

> `Module#constants` is inconsistent with the predicates.

I understand this. This issue is observable in the code I wrote in #note-1. I think that, in the context of requiring foo.rb, `Module#constants` should not contain `:Foo` until it is actually defined.

----------------------------------------
Misc #21035: Clarify or redefine Module#autoload? and Module#const_defined?
https://bugs.ruby-lang.org/issues/21035#change-111901

* Author: fxn (Xavier Noria)
* Status: Open
----------------------------------------
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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