From a1ee420aea398d58b20842aef12145d07f908602 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Thu, 19 Feb 2026 17:26:04 +0900
Subject: [PATCH] test/t/syntax.rb: add test for `&nil` in formal parameters

Co-authored-by: Claude <noreply@anthropic.com>
---
 test/t/syntax.rb | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/test/t/syntax.rb b/test/t/syntax.rb
index 3e9495823..42a6d4198 100644
--- a/test/t/syntax.rb
+++ b/test/t/syntax.rb
@@ -1271,3 +1271,26 @@ assert('pattern matching - complex patterns') do
     assert_equal [2, 3], rest
   end
 end
+
+assert('&nil in formal parameters') do
+  def m(&nil); end
+  m
+  m(&nil)
+  assert_raise(ArgumentError) { m {} }
+
+  def m2(a, b, &nil); end
+  m2(1, 2)
+  assert_raise(ArgumentError) { m2(1, 2) {} }
+
+  def m3(a, b=1, *c, &nil); end
+  m3(1)
+  assert_raise(ArgumentError) { m3(1) {} }
+
+  def m4(a:, &nil); end
+  m4(a: 1)
+  assert_raise(ArgumentError) { m4(a: 1) {} }
+
+  f = ->(&nil) { :ok }
+  assert_equal :ok, f.call
+  assert_raise(ArgumentError) { f.call {} }
+end