[ruby-core:66145] [ruby-trunk - Bug #10488] [Open] Consistency of Module#const_defined? and constant lookup

Issue #10488 has been reported by Benoit Daloze.

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Bug #10488: Consistency of Module#const_defined? and constant lookup
https://bugs.ruby-lang.org/issues/10488

* Author: Benoit Daloze
* Status: Open
* Priority: Normal
* Assignee: 
* Category: core
* Target version: current: 2.2.0
* ruby -v: ruby 2.2.0dev (2014-10-12 trunk 47890) [x86_64-darwin13]
* Backport: 
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Currently, if for some module `mod` and constant `Const`,
`mod.const_defined?(:Const)` is true does not imply `mod::Const` is not an error.

This is inconsistent for at least the following cases:

* if mod is a Module but not a class, const_defined? will look in Object and its ancestors, but constant access (::) will not look in Object or above.

    Enumerable.const_defined? :String
    Enumerable::String #=> NameError: uninitialized constant Enumerable::String

* if Const is private, const_defined? will return true while mod::Const will raise an error.

    C = 42
    Object.private_constant :C
    String.const_defined? :C #=> true
    String::C #=> NameError: private constant String::C referenced

    # This works, but is due to the lexical scope lookup
    class String
      C #=> 42
    end

Is this intended?
Should it not mirror the behavior of defined?(mod::Const)?
Or the behavior of method_defined?



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