Dup hash with keyword flag when converted to keywords

When ruby2_keywords is used on a method, keywords passed to the method
are flagged.  When the hash is passed as the last element of an
argument splat to another method, the hash should be treated as a
keyword splat.  When keyword splatting a hash, a duplicate of the
hash is made.  So when auto-splatting the hash with the keyword
flag, a duplicate of the hash should also be made.

This fixes cases where the hash is later passed to another method
and would be treated as keywords there:

  class Object
    ruby2_keywords def foo(*a) bar(*a) end
    def bar(*a) baz(*a) end
    def baz(*a, **kw) [a, kw] end
  end
  foo(:a=>1)

Previously, this would pass the :a=>1 as keywords to bar and also as
keywords to baz. Now it only passes :a=>1 as keywords to bar, but bar
passes :a=>1 as a positional hash to baz (which in this case
generates a warning in 2.7).

0 files changed, 0 insertions, 0 deletions