From cb303ff4b82dca932cb7342e9f7fd337d69dc175 Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Sat, 6 Dec 2025 08:48:29 +0900
Subject: [Bug #21669] Fix void value expression check for pattern-matching

If the all `in` and `else` branches are void, the `case` is also void.
---
 parse.y                  | 26 ++++++++++++++++++--------
 test/ruby/test_syntax.rb | 12 ++++++++++++
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/parse.y b/parse.y
index a872eb61a3..b874e4f8dc 100644
--- a/parse.y
+++ b/parse.y
@@ -13877,15 +13877,25 @@ value_expr_check(struct parser_params *p, NODE *node)
             break;
 
           case NODE_CASE3:
-            if (!RNODE_CASE3(node)->nd_body || !nd_type_p(RNODE_CASE3(node)->nd_body, NODE_IN)) {
-                compile_error(p, "unexpected node");
-                return NULL;
-            }
-            if (RNODE_IN(RNODE_CASE3(node)->nd_body)->nd_body) {
-                return NULL;
+            {
+                NODE *in = RNODE_CASE3(node)->nd_body;
+                if (!in || !nd_type_p(in, NODE_IN)) {
+                    compile_error(p, "unexpected node");
+                    return NULL;
+                }
+                if (!RNODE_IN(in)->nd_body) {
+                    /* single line pattern matching with "=>" operator */
+                    goto found;
+                }
+                do {
+                    vn = value_expr_check(p, RNODE_IN(in)->nd_body);
+                    if (!vn) return NULL;
+                    if (!void_node) void_node = vn;
+                    in = RNODE_IN(in)->nd_next;
+                } while (in && nd_type_p(in, NODE_IN));
+                node = in;  /* else */
             }
-            /* single line pattern matching with "=>" operator */
-            goto found;
+            break;
 
           case NODE_BLOCK:
             while (RNODE_BLOCK(node)->nd_next) {
diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index 1ea646d216..e868967e8b 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -2132,6 +2132,18 @@ eom
     };
   end
 
+  def test_value_expr_in_case3
+    assert_syntax_error("#{<<~"{#"}\n#{<<~'};'}", /void value expression/, nil, "#{BUG_21669} 1.3")
+    {#
+      x =
+        case a
+        in 1; return
+        in 2; return
+        else return
+        end
+    };
+  end
+
   def test_tautological_condition
     assert_valid_syntax("def f() return if false and invalid; nil end")
     assert_valid_syntax("def f() return unless true or invalid; nil end")
-- 
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