Don't leak Object constants in core_ext/module/qualified_const

[gsamokovarov]

Bumped on this one recently.

Actually, I think we can remove this altogether for Rails 5. Since Ruby 2, Object.const_get actually works for qualified constant names and doesn't raises an exception for absolute paths anymore.

>> Object.const_get '::String'
=> String
>> RUBY_VERSION
=> "2.1.4"
>> Object.const_get '::ActiveSupport::OrderedOptions'
=> ActiveSupport::OrderedOptions

I grepped the code and its not used anywhere but its test.

♡  ag "qualified_const_get"
activesupport/lib/active_support/core_ext/module/qualified_const.rb
26:# Object.const_get('::String') raises NameError and so does qualified_const_get.
39:  def qualified_const_get(path)
52:    mod = mod_name.empty? ? self : qualified_const_get(mod_name)

activesupport/test/core_ext/module/qualified_const_test.rb
59:  test "qualified_const_get" do
60:    assert_equal false, Object.qualified_const_get("QualifiedConstTestMod::X")
61:    assert_equal false, QualifiedConstTestMod.qualified_const_get("X")
62:    assert_equal 1, QualifiedConstTestMod.qualified_const_get("M::X")
63:    assert_equal 1, QualifiedConstTestMod.qualified_const_get("N::X")
64:    assert_equal 2, QualifiedConstTestMod.qualified_const_get("M::C::X")
66:    assert_raise(NameError) { QualifiedConstTestMod.qualified_const_get("M::C::Y")}
95:    assert_raise_with_message(NameError, "wrong constant name ::X") { Object.qualified_const_get("::X")}
96:    assert_raise_with_message(NameError, "wrong constant name ::X") { Object.qualified_const_get("::X::Y")}

guides/source/3_2_release_notes.md
508:* Defined new methods `Module#qualified_const_defined?`, `Module#qualified_const_get` and `Module#qualified_const_set` that are analogous to the corresponding methods in the standard API, but accept qualified constant names.

guides/source/active_support_core_extensions.md
748:The new methods are `qualified_const_defined?`, `qualified_const_get`, and
754:Object.qualified_const_get("Math::PI")            # => 3.141592653589793
761:Math.qualified_const_get("E") # => 2.718281828459045
1704:  mod = mod_name.empty? ? self : qualified_const_get(mod_name)

[rafaelfranca]

That class was public. So we would have to deprecate all the code.

[gsamokovarov]

Tried doing that and the whole test suite light up with deprecation warnings.

Module#qualified_const_defined? is used throughout the autoloading code and new Module#const_defined? doesn't have the same semantics. Its only Module#const_get that behaves similarly to Module#qualified_const_get.

Maybe we can implement Module#qualified_const_get in terms of native Module#const_get for speed, but other than that, we won't be able to touch the other methods.

[rafaelfranca]

cc @fxn

[fxn]

ACK!

I am in an immersion working on the contrib app these days, gonna get back here soon.

[fxn]

I have removed internal usage. I think we should just deprecate these extensions for later removal.

[gsamokovarov]

@fxn I can try to issue a deprecation warning only once, so we don't flood logs with them. Should I do it in this PR?

[fxn]

Hmmm.... in principle we could warn always, that's how we normally do it. @rafaelfranca WDYT?

[sgrif]

@gsamokovarov Are you still interested in working on this? I agree that we should always warn, not warn once.

[gsamokovarov]

@sgrif Sure! Deprecated the qualified_const_ methods, fixed deprecations in the tests and added a changelog entry.