[ruby-core:109249] [Ruby master Bug#18927] Can't access class variable directly with class inheritance

Issue #18927 has been reported by jemmai (Jemma Issroff).

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Bug #18927: Can't access class variable directly with class inheritance
https://bugs.ruby-lang.org/issues/18927

* Author: jemmai (Jemma Issroff)
* Status: Open
* Priority: Normal
* ruby -v: 3.1.2
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
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If a child class inherits from a parent class, and the child class sets a class variable, the parent class can't access the class variable literal:

```
class Parent
  def self.class_var
    puts @@class_var
  end
end

class Child < Parent
  @@class_var = "class_var"
end

Child.class_var

# => test.rb:3:in `class_var': uninitialized class variable @@class_var in Parent (NameError)
```

Confusingly, if we use `class_variable_get` (method lookup) to access `@@class_var`, we can access it as expected. We can alter the snippet from above to see this behavior:

```
class Parent
  def self.class_var
    puts class_variable_get(:@@class_var)
    puts @@class_var
  end
end

class Child < Parent
  @@class_var = "class_var"
end

Child.class_var

# => "class_var"
# => test.rb:4:in `class_var': uninitialized class variable @@class_var in Parent (NameError)
```


## Is this desired behavior?

`self` is the subclass so it seems like the class variable should be looked up on the receiver. Why is the method lookup resolution different than the literal? Should it be different?



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