From 42501015b4ffac67671cc5e1daedbacf5840d71b Mon Sep 17 00:00:00 2001
From: Matt Valentine-House <matt@eightbitraptor.com>
Date: Mon, 11 Nov 2024 12:04:12 +0000
Subject: [PATCH] rb_raise when attempting to set the GC implementation name

Instead of silently ignoring the key, we should raise to clearly tell
the user that this key is read-only.
---
 gc.rb                | 10 +++++++++-
 test/ruby/test_gc.rb |  4 +---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/gc.rb b/gc.rb
index 2a75e166ce..f3221c5761 100644
--- a/gc.rb
+++ b/gc.rb
@@ -306,7 +306,15 @@ module GC
   def self.config hash = nil
     return Primitive.gc_config_get unless hash
 
-    Primitive.gc_config_set hash
+    if(Primitive.cexpr!("RBOOL(RB_TYPE_P(hash, T_HASH))"))
+      if hash.include?(:implementation)
+        raise ArgumentError, 'Attempting to set read-only key "Implementation"'
+      end
+
+      Primitive.gc_config_set hash
+    else
+      raise ArgumentError
+    end
   end
 
   # call-seq:
diff --git a/test/ruby/test_gc.rb b/test/ruby/test_gc.rb
index 1eb5451b3f..72fab5c43c 100644
--- a/test/ruby/test_gc.rb
+++ b/test/ruby/test_gc.rb
@@ -127,9 +127,7 @@ class TestGc < Test::Unit::TestCase
   def test_gc_config_implementation_is_readonly
     omit unless /darwin|linux/.match(RUBY_PLATFORM)
 
-    impl = GC.config[:implementation]
-    GC.config(implementation: "somethingelse")
-    assert_equal(impl, GC.config[:implementation])
+    assert_raise(ArgumentError) { GC.config(implementation: "somethingelse") }
   end
 
   def test_start_full_mark