[PRISM] Fix fallthrough for PM_ENSURE_NODE

This caused it to fall into PM_ELSE_NODE which caused ensure nodes to be
compiled twice.

Fixes ruby/prism#2176.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/ruby/test_compile_prism.rb b/test/ruby/test_compile_prism.rb
index c0f85af8b4..d547f82fe3 100644
--- a/test/ruby/test_compile_prism.rb
+++ b/test/ruby/test_compile_prism.rb
@@ -931,6 +931,21 @@ module Prism
         end
         a
       CODE
+
+      # Test that ensure block only evaluated once
+      assert_prism_eval(<<~RUBY)
+        res = []
+        begin
+          begin
+            raise
+          ensure
+            res << $!.to_s
+          end
+        rescue
+          res
+        end
+      RUBY
+
       assert_prism_eval(<<-CODE)
         a = 1
         begin