Fix incorrect use of VM_CALL_KW_SPLAT_MUT in zsuper with keyword splat

For zsuper calls with a keyword splat but no actual keywords, the
keyword splat is passed directly, so it cannot be mutable, because
if the callee accepts a keyword splat, changes to the keyword splat
by the callee would be reflected in the caller.

While here, simplify the logic when the method supports
literal keywords.  I don't think it is possible for
a method with has_kw param flags to not have keywords, so add an
assertion for that, and set VM_CALL_KW_SPLAT_MUT in a single place.

1 files changed, 12 insertions, 0 deletions

diff --git a/test/ruby/test_super.rb b/test/ruby/test_super.rb
index 6a575b88c5..ce78e66c52 100644
--- a/test/ruby/test_super.rb
+++ b/test/ruby/test_super.rb
@@ -558,6 +558,18 @@ class TestSuper < Test::Unit::TestCase
     end
   end
 
+  def test_zsuper_kw_splat_not_mutable
+    extend(Module.new{def a(**k) k[:a] = 1 end})
+    extend(Module.new do
+      def a(**k)
+        before = k.dup
+        super
+        [before, k]
+      end
+    end)
+    assert_equal(*a)
+  end
+
   def test_from_eval
     bug10263 = '[ruby-core:65122] [Bug #10263a]'
     a = Class.new do