From 6409715212d22699bd2751a363b050a5d8b94b83 Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Tue, 2 Dec 2025 17:34:36 -0800
Subject: Fix allocationless anonymous splat keyword argument check

Previously, if an argument splat and keywords are provided by
the caller, it did not check whether the method/proc accepted
keywords before avoiding the allocation. This is incorrect,
because if the method/proc does not accept keywords, the
keywords passed by the caller are added as a positional
argument, so there must be an allocation to avoid mutating
the positional splat argument.

Add a check that if the caller passes keywords, the
method/proc must accept keywords in order to optimize.
If the caller passes a keyword splat, either the
method/proc must accept keywords, or the keyword splat must
be empty in order to optimize.

If keywords are explicitly disallowed via `**nil`, the
optimization should be skipped, because the array is mutated
before the ArgumentError exception is raised.

In addition to a test for the correct behavior, add an
allocation test for a method that accepts an anonymous splat
without keywords.

Fixes [Bug #21757]
---
 test/ruby/test_allocation.rb | 53 ++++++++++++++++++++++++++++++++++++++++++++
 test/ruby/test_call.rb       | 29 ++++++++++++++++++++++++
 2 files changed, 82 insertions(+)

(limited to 'test/ruby')

diff --git a/test/ruby/test_allocation.rb b/test/ruby/test_allocation.rb
index 6ade391c95..90d7c04f9b 100644
--- a/test/ruby/test_allocation.rb
+++ b/test/ruby/test_allocation.rb
@@ -527,6 +527,59 @@ class TestAllocation < Test::Unit::TestCase
       RUBY
     end
 
+    def test_anonymous_splat_parameter
+      only_block = block.empty? ? block : block[2..]
+      check_allocations(<<~RUBY)
+        def self.anon_splat(*#{block}); end
+
+        check_allocations(1, 1, "anon_splat(1, a: 2#{block})")
+        check_allocations(1, 1, "anon_splat(1, *empty_array, a: 2#{block})")
+        check_allocations(1, 1, "anon_splat(1, a:2, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(1, **empty_hash, a: 2#{block})")
+
+        check_allocations(1, 0, "anon_splat(1, **nil#{block})")
+        check_allocations(1, 0, "anon_splat(1, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(1, **hash1#{block})")
+        check_allocations(1, 1, "anon_splat(1, *empty_array, **hash1#{block})")
+        check_allocations(1, 1, "anon_splat(1, **hash1, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(1, **empty_hash, **hash1#{block})")
+
+        check_allocations(1, 0, "anon_splat(1, *empty_array#{block})")
+        check_allocations(1, 0, "anon_splat(1, *empty_array, *empty_array, **empty_hash#{block})")
+
+        check_allocations(1, 1, "anon_splat(*array1, a: 2#{block})")
+
+        check_allocations(0, 0, "anon_splat(*nil, **nill#{block})")
+        check_allocations(0, 0, "anon_splat(*array1, **nill#{block})")
+        check_allocations(0, 0, "anon_splat(*array1, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(*array1, **hash1#{block})")
+        check_allocations(1, 1, "anon_splat(*array1, *empty_array, **hash1#{block})")
+
+        check_allocations(1, 0, "anon_splat(*array1, *empty_array#{block})")
+        check_allocations(1, 0, "anon_splat(*array1, *empty_array, **empty_hash#{block})")
+
+        check_allocations(1, 1, "anon_splat(*array1, *empty_array, a: 2, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(*array1, *empty_array, **hash1, **empty_hash#{block})")
+
+        check_allocations(0, 0, "anon_splat(#{only_block})")
+        check_allocations(1, 1, "anon_splat(a: 2#{block})")
+        check_allocations(0, 0, "anon_splat(**empty_hash#{block})")
+
+        check_allocations(1, 1, "anon_splat(1, *empty_array, a: 2, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(1, *empty_array, **hash1, **empty_hash#{block})")
+        check_allocations(1, 1, "anon_splat(*array1, **empty_hash, a: 2#{block})")
+        check_allocations(1, 1, "anon_splat(*array1, **hash1, **empty_hash#{block})")
+
+        unless defined?(RubyVM::YJIT.enabled?) && RubyVM::YJIT.enabled?
+          check_allocations(0, 0, "anon_splat(*array1, **nil#{block})")
+          check_allocations(1, 0, "anon_splat(*r2k_empty_array#{block})")
+          check_allocations(1, 1, "anon_splat(*r2k_array#{block})")
+          check_allocations(1, 0, "anon_splat(*r2k_empty_array1#{block})")
+          check_allocations(1, 1, "anon_splat(*r2k_array1#{block})")
+        end
+      RUBY
+    end
+
     def test_anonymous_splat_and_anonymous_keyword_splat_parameters
       only_block = block.empty? ? block : block[2..]
       check_allocations(<<~RUBY)
diff --git a/test/ruby/test_call.rb b/test/ruby/test_call.rb
index 7843f3b476..1b30ed34d8 100644
--- a/test/ruby/test_call.rb
+++ b/test/ruby/test_call.rb
@@ -423,6 +423,35 @@ class TestCall < Test::Unit::TestCase
     assert_equal([1, 2, {}], s(*r2ka))
   end
 
+  def test_anon_splat_mutated_bug_21757
+    args = [1, 2]
+    kw = {bug: true}
+
+    def self.m(*); end
+    m(*args, bug: true)
+    assert_equal(2, args.length)
+
+    proc = ->(*) { }
+    proc.(*args, bug: true)
+    assert_equal(2, args.length)
+
+    def self.m2(*); end
+    m2(*args, **kw)
+    assert_equal(2, args.length)
+
+    proc = ->(*) { }
+    proc.(*args, **kw)
+    assert_equal(2, args.length)
+
+    def self.m3(*, **nil); end
+    assert_raise(ArgumentError) { m3(*args, bug: true) }
+    assert_equal(2, args.length)
+
+    proc = ->(*, **nil) { }
+    assert_raise(ArgumentError) { proc.(*args, bug: true) }
+    assert_equal(2, args.length)
+  end
+
   def test_kwsplat_block_eval_order
     def self.t(**kw, &b) [kw, b] end
 
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