From: "fxn (Xavier Noria)" <noreply@...>
Date: 2022-03-11T18:56:25+00:00
Subject: [ruby-core:107849] [Ruby master Bug#18622] const_get still looks in Object, while lexical constant lookup no longer does

Issue #18622 has been updated by fxn (Xavier Noria).


I do not know which is the correct definition of `const_get`, Ruby core knows :).

However, let me say that I have always thought about `const_get` as what happens during a _relative_ constant lookup. That is, in my mind, a relative constant lookup is basically: 1) Check the nesting + 2) `const_get` (conceptually, and includes `const_missing` if needed).

Take for example:

```ruby
Module.new.const_get(:String) # => String
```

You get `String` there, but it is not in the ancestors. Why? Because it is checking `Object` by hand, like the relative constant lookup algorithm does.

I believe

```ruby
String.const_get(:Hash) # =>
```

has to be understood that way.

----------------------------------------
Bug #18622: const_get still looks in Object, while lexical constant lookup no longer does
https://bugs.ruby-lang.org/issues/18622#change-96789

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
There is some inconsistency here between literal constant lookup and the meta API (const_get).

Lexical constant lookup no longer uses a special case for Object, and this is good as it avoids surprises: #11547

However, `const_get` still looks in Object, even though that's confusing, inconsistent and IMHO shouldn't really happen.
```ruby
module ConstantSpecsTwo
  Foo = :cs_two_foo
end

module ConstantSpecs
end

p ConstantSpecs.const_get("ConstantSpecsTwo::Foo") # => :cs_two_foo
p ConstantSpecs::ConstantSpecsTwo::Foo # => const_get.rb:9:in `<main>': uninitialized constant ConstantSpecs::ConstantSpecsTwo (NameError)
```

I think we should change it so both behave the same (i.e., NameError).
It's like if `cd /foo/bar` would go to `/bar` if `/foo/bar` does not exist and `/bar` does.

`const_get` is a meta API so it cannot know the surrounding `Module.nesting`, but so I think it should consider the receiver of `const_get` as the only nesting (so just `ConstantSpecs` in this case, not `Object`).

Note this does not affect nested constants inside the `const_get` like `Foo` above (another way to look at the inconsistency that the first component is treated differently).

From https://bugs.ruby-lang.org/issues/11547#note-19



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