Splat with method_missing inconsistent

[endofunky]

The behavior when using the splat operator together with method_missing appears to be different from MRI.

Example:

class A
  attr_reader :obj

  def initialize(*args)
    @obj = args
  end

  def method_missing(method, *args, &block)
    if obj.respond_to?(method)
      obj.__send__(method, *args, &block)
    else
      super
    end
  end
end

On MRI:

a = A.new(*A.new([1,2,3]), *A.new([3,4,5]))

puts a.inspect
# => #<A:0x007fcba58d07c0 @obj=[[1, 2, 3], [3, 4, 5]]>

puts a.obj.first.class.name
# => Array

On JRuby 9.0.0 SNAPSHOT:

a = A.new(*A.new([1,2,3]), *A.new([3,4,5]))

puts a.inspect
# => #<A:0x6e38921c @obj=[#<A:0x27c6e487 @obj=[[1, 2, 3]]>, #<A:0x38364841 @obj=[[3, 4, 5]]>]>

puts a.obj.first.class.name
# => A

[headius]

Confirmed in both interpreter and JIT. High priority.

Seems like it's not coercing to array, so perhaps it's checking if to_ary is defined before making the call when it should just go for it?

[headius]

Yeah it seems to be an IR problem. If I log the method name in method_missing, I see it called twice for MRI and zero times for JRuby 9k. So splatting is not making the call it should in this place.

@subbuss You did work on splatting recently...perhaps take a look into this?

[subbuss]

looking..

[subbuss]

Seems like a bug in Helpers.arrayValue(..) else part of line 1862 .. it is unconditionally returning a new array instead of calling method_missing .. but since these helpers have been around for ever, I don't want to just fix it. But, fixing it there would fix it .. or maybe IRRuntimeHelpers:irSplat is not calling the right helper in Helpers.java. Is this good enough for you or @enebo to take this over?

[subbuss]

Please review my fix and close if it looks good. Will require new tests since this hasn't been covered by any suite so far?

[subbuss]

fwiw, I tested with the above snippet and also by making method_missing return a Fixnum and both MRI and 9k now raise an error.

[endofunky]

I just saw the ``to_a' did not return Array` error you're raising and had a look what MRI does in that case.

class A
  attr_reader :obj

  def initialize(*args)
    @obj = args
  end

  def method_missing(method, *args, &block)
    if obj.respond_to?(method)
      obj.__send__(method, *args, &block)
    else
      super
    end
  end
end

class B < Array
  def to_a
    nil
  end
end

b = B.new
b.push 3
b.push 4
b.push 5

a = A.new(*A.new([1,2,3]), *A.new(b))

puts b.to_a.inspect
puts b.class.name
puts a.inspect

MRI output:

nil
B
#<A:0x007fd49809d4a8 @obj=[[1, 2, 3], [3, 4, 5]]>

I didn't expect this to work. May be this is actually undefined behavior? Or am I missing something here?

[endofunky]

Actually have a one more. Given to_a returns nil and B isn't a subclass of Array:

class A
  attr_reader :obj

  def initialize(*args)
    @obj = args
  end

  def method_missing(method, *args, &block)
    puts "called"
    if obj.respond_to?(method)
      obj.__send__(method, *args, &block)
    else
      super
    end
  end
end

class B
  def to_a
    nil
  end
end

b = B.new

puts b.to_a.inspect
puts b.class.name

a = A.new(*A.new([1,2,3]), *A.new(b))

puts a.inspect

MRI output:

nil
B
called
called
#<A:0x007fed27215a40 @obj=[[1, 2, 3], #<B:0x007fed27215db0>]>

I added in a puts to make sure method_missing is even getting called. The above result is the same even if B#to_a returns any other type, such as Fixnum, or if the method isn't defined at all.

[subbuss]

jruby current master returns identical output as MRI in both cases.

[subbu@earth api] jruby -X-C /tmp/bug.rb
nil
B
#<A:0x4da8846f @obj=[[1, 2, 3], [3, 4, 5]]>

and

[subbu@earth api] jruby -X-C /tmp/bug.rb
nil
B
called
called
#<A:0x126f5e8d @obj=[[1, 2, 3], #<B:0x78a6dc8c>]>

When to_a returns nil, the default behavior is to return an empty array. See the jruby commit that fixes this bug to see the code.

[headius]

It sounds like this one is fixed. @tobiassvn If you are seeing the original reported behavior failing, please reopen and demonstrate. If you are seeing related but different behaviors failing, file a new issue.