Bug #15457: Weird behaviour when having multiple arguments of same name and splat operator

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 2.5.3
• Backport: 2.4: UNKNOWN, 2.5: UNKNOWN

[graywolf (Gray Wolf)]

When multiple arguments of the same name are provided and last one of
them has splat operator, everything gets weird.

+   $ cat bug.rb
def test(_a, b, *_a)
  pp _a
  pp b
end
test(*%W{a b c d e})

+   $ RUBYOPT=-rpry rvm 2.5.3 do ruby bug.rb
["c", "d", "e"]
nil

+   $ RUBYOPT=-rpry rvm 2.4.5 do ruby bug.rb
["c", "d", "e"]
nil

+   $ RUBYOPT=-rpry rvm 2.3.8 do ruby bug.rb
["c", "d", "e"]
nil

At least it's consistent across supported ruby versions, but I have no
idea what is going on.

I get why _a is %w{c d e}, that makes sense. But why is b nil?
That makes no sense at all.

It looks to me like an edge case when having multiple arguments of the same
name and one of them (last one?) having splat operator.

[graywolf (Gray Wolf)]

• Description updated (diff)

[mame (Yusuke Endoh)]

• Related to Bug #14611: Exotic method parameters bug added

[mame (Yusuke Endoh)]

• Status changed from Open to Closed

Thank you. This is duplicate of #14611. The behavior has been changed in trunk (and 2.6).

$ cat bug.rb
def test(_a, b, *_a)
  pp _a
  pp b
end
test(*%W{a b c d e})

$ ./local/bin/ruby -v bug.rb 
ruby 2.6.0dev (2018-12-24 trunk 66525) [x86_64-linux]
"a"
"b"

#14611 is marked as backport required. Please wait.