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).

1 files changed, 2 insertions, 0 deletions

diff --git a/vm_args.c b/vm_args.c
index 92deef5586..6fce593bf1 100644
--- a/vm_args.c
+++ b/vm_args.c
@@ -737,6 +737,8 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
         if (!kw_flag && len > 0) {
             if (RB_TYPE_P(rest_last, T_HASH) &&
                 (((struct RHash *)rest_last)->basic.flags & RHASH_PASS_AS_KEYWORDS)) {
+                rest_last = rb_hash_dup(rest_last);
+                RARRAY_ASET(args->rest, len - 1, rest_last);
                 kw_flag |= VM_CALL_KW_SPLAT;
             }
             else {