Bug #18806: protected methods defined by refinements can't be called

• Status: Closed
• Assignee: shugo (Shugo Maeda)
• Target version: -
• ruby -v: ruby 3.2.0dev
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[jhawthorn (John Hawthorn)]

Hello!

The protected visibility is a bit unusual, since it depends on where the callee method is considered to be defined. I was looking into making an optimization to calling protected methods on self, and we came across some surprising behaviour. (Thanks @alanwu (Alan Wu) for finding!)

As far as I can tell, there is no way to call a method refined method is protected visibility (other than send).

class A
end

module MyRefine
  refine(A) {
    private def private_foo = :refined
    def private_foo_in_refinement = private_foo

    protected def protected_foo = :refined
    def protected_foo_in_refinement = protected_foo
  }
end

class A
  using MyRefine

  def call_private = private_foo
  def call_private_through_refinement = private_foo_in_refinement

  def call_protected = protected_foo
  def call_protected_through_refinement = protected_foo_in_refinement
  def is_defined = defined?(protected_foo)
end



A.new.call_private
# => :refined

A.new.call_private_through_refinement
# => :refined

A.new.call_protected
# => NoMethodError: protected method `protected_foo' called for #<A:0x00007f23f35e9390>

A.new.call_protected_through_refinement
# => NoMethodError: protected method `protected_foo' called for #<A:0x00007f23f35e9390>

A.new.is_defined
# "method"

I find it confusing that here protected is more restrictive than private (private methods from a refinement can be called as normal), but I'm not sure if it's a rule that it should be or just how I've always assumed it is.

It's also odd that defined? returns truthy, but I think this might actually be a bug on defined with protected methods (behaviour doesn't match that of method calls).

I think this is probably not intentional or desired behaviour. It's not useful for us to make methods which can't be called. The reason this happens I think is an implementation detail: the "defined class" of the method we're trying to call is the ICLASS including the refinement module onto the A superclass.

Possible options I see for improving this:

1. Treat defined methods as though they were defined on the refined class. Both examples above will now work, and it is possible to call the refined method on objects other than self.

2. Always allow "fcalls" to protected methods. Making them basically an alias for private when used in a refinement.

3. Forbid using protected inside a refinement (and Refinement#import_methods), raising an error.

My preference would be 1. I think it would require one extra check when calling protected methods, but calling protected methods is already a slower path so I think it is fine.

Thanks for reading!

[Eregon (Benoit Daloze)]

I agree this looks like unintended behavior/a bug.

TruffleRuby already behaves like:

:refined
:refined
:refined
:refined
"method"

fcalls should ignore visibility, always, so I think 2. is best.

[shugo (Shugo Maeda)]

protected is for a method call with an explicit receiver, so I prefer 1.

private is enough for fcalls.

[Eregon (Benoit Daloze)]

Right, agreed that 1 is best semantically.
I'm not too keen on extra checks, but the checks for protected are already expensive and this won't make it significantly worse.

1 implies 2 BTW in terms of optimizations, i.e., if it's an fcall no need to check any visibility.

[shugo (Shugo Maeda)]

• Assignee set to matz (Yukihiro Matsumoto)

Eregon (Benoit Daloze) wrote in #note-3:

I'm not too keen on extra checks, but the checks for protected are already expensive and this won't make it significantly worse.

Agreed.

Matz, can I change protected methods defined by refinements as follows?

1. Treat defined methods as though they were defined on the refined class. Both examples above will now work, and it is possible to call the refined method on objects other than self.

[jhawthorn (John Hawthorn)]

Patch implementing option 1: https://github.com/ruby/ruby/pull/5966

[matz (Yukihiro Matsumoto)]

• Assignee changed from matz (Yukihiro Matsumoto) to shugo (Shugo Maeda)

The option 1 is accepted.

Matz.

[jhawthorn (John Hawthorn)]

• Status changed from Open to Closed

Applied in changeset git|ae163cae6b3f01e0fb827e0a18d5889f9703617f.

---

Allow calling protected methods from refinements

Previously protected methods on refinements could never be called
because they were seen as being "defined" on the hidden refinement
ICLASS.

This commit updates calling refined protected methods so that they are
considered to be defined on the original class (the one being refined).

This ended up using the same behaviour that was used to check whether a
call to super was allowed, so I extracted that into a method.

[Bug #18806]