[Bug #21669] Implement void value expression check for `case`/`when`

If the all `when` and `else` branches are void, the `case` is also
void.

1 files changed, 24 insertions, 0 deletions

diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index 9a14375056..3638d83e2b 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -2053,6 +2053,30 @@ eom
     };
   end
 
+  def test_value_expr_in_case
+    assert_syntax_error("#{<<~"{#"}\n#{<<~'};'}", /void value expression/, nil, "#{BUG_21669} 1.3")
+    {#
+      x =
+        case a
+        when 1; return
+        when 2; return
+        else return
+        end
+    };
+  end
+
+  def test_value_expr_in_case2
+    assert_syntax_error("#{<<~"{#"}\n#{<<~'};'}", /void value expression/, nil, "#{BUG_21669} 1.3")
+    {#
+      x =
+        case
+        when 1; return
+        when 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")