From c1d8829ef515ee51fadeadd7dd022b5c47a71cdd Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Fri, 24 Jan 2020 12:13:41 -0800
Subject: [PATCH] Do not autosplat when calling proc with empty keyword splat

With the removal of the splatted argument when using an empty
keyword splat, the autosplat code considered an empty keyword
splat the same as no argument at all.  However, that results
in autosplat behavior changing dependent on the content of
the splatted hash, which is not what anyone would expect or
want.  This change always skips an autosplat if keywords were
provided.

Fixes [Bug #16560]
---
 test/ruby/test_proc.rb | 20 ++++++++++++++++++++
 vm_args.c              |  3 ++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/test/ruby/test_proc.rb b/test/ruby/test_proc.rb
index af4cf11623..4177707ddd 100644
--- a/test/ruby/test_proc.rb
+++ b/test/ruby/test_proc.rb
@@ -1087,6 +1087,26 @@ class TestProc < Test::Unit::TestCase
     assert_equal([1,2,[3],4,5], r, "[ruby-core:19485]")
   end
 
+  def test_proc_autosplat
+    def self.a(arg, kw)
+      yield arg
+      yield arg, **kw
+      yield arg, kw
+    end
+
+    arr = []
+    a([1,2,3], {}) do |arg1, arg2=0|
+      arr << [arg1, arg2]
+    end
+    assert_equal([[1, 2], [[1, 2, 3], 0], [[1, 2, 3], {}]], arr)
+
+    arr = []
+    a([1,2,3], a: 1) do |arg1, arg2=0|
+      arr << [arg1, arg2]
+    end
+    assert_equal([[1, 2], [[1, 2, 3], {a: 1}], [[1, 2, 3], {a: 1}]], arr)
+  end
+
   def test_proc_single_arg_with_keywords_accepted_and_yielded
     def self.a
       yield [], **{a: 1}
diff --git a/vm_args.c b/vm_args.c
index 256ab5b7f4..13d4e4a545 100644
--- a/vm_args.c
+++ b/vm_args.c
@@ -445,9 +445,9 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
 {
     const int min_argc = iseq->body->param.lead_num + iseq->body->param.post_num;
     const int max_argc = (iseq->body->param.flags.has_rest == FALSE) ? min_argc + iseq->body->param.opt_num : UNLIMITED_ARGUMENTS;
-    int opt_pc = 0;
     int given_argc;
     unsigned int kw_flag = ci->flag & (VM_CALL_KWARG | VM_CALL_KW_SPLAT);
+    int opt_pc = 0, allow_autosplat = !kw_flag;
     struct args_info args_body, *args;
     VALUE keyword_hash = Qnil;
     VALUE * const orig_sp = ec->cfp->sp;
@@ -573,6 +573,7 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
 	break; /* do nothing special */
       case arg_setup_block:
         if (given_argc == (keyword_hash == Qnil ? 1 : 2) &&
+            allow_autosplat &&
 	    (min_argc > 0 || iseq->body->param.opt_num > 1 ||
 	     iseq->body->param.flags.has_kw || iseq->body->param.flags.has_kwrest) &&
 	    !iseq->body->param.flags.ambiguous_param0 &&