From 4b14b2902abaa0e8f0d1e8282d2322f47431fa3f Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Tue, 22 Mar 2022 16:36:16 -0700
Subject: [PATCH] Uncomment code to raise LocalJumpError for yield across
 thread through enum

Not sure if this is the correct fix.  It does raise LocalJumpError in
the yielding thread as you would expect, but the value yielded to the calling
thread is still yielded without an exception.

Fixes [Bug #18649]
---
 test/ruby/test_thread.rb | 55 ++++++++++++++++++++++++++++++++++++++++
 vm.c                     |  2 --
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/test/ruby/test_thread.rb b/test/ruby/test_thread.rb
index e80ca16022..ddb4516b3c 100644
--- a/test/ruby/test_thread.rb
+++ b/test/ruby/test_thread.rb
@@ -1338,6 +1338,61 @@ q.pop
     t.join
   end
 
+  def test_yield_across_thread_through_enum
+    bug18649 = '[ruby-core:107980] [Bug #18649]'
+    @log = []
+
+    def self.p(arg)
+      @log << arg
+    end
+
+    def self.synchronize
+      yield
+    end
+
+    def self.execute(task)
+      success = true
+      value = reason = nil
+      end_sync = false
+
+      synchronize do
+        begin
+          p :before
+          value = task.call
+          p :never_reached
+          success = true
+        rescue StandardError => ex
+          ex = ex.class
+          p [:rescue, ex]
+          reason = ex
+          success = false
+        end
+
+        end_sync = true
+        p :end_sync
+      end
+
+      p :should_not_reach_here! unless end_sync
+      [success, value, reason]
+    end
+
+    def self.foo
+      Thread.new do
+        result = execute(-> { yield 42 })
+        p [:result, result]
+      end.join
+    end
+
+    value = to_enum(:foo).first
+    expected = [:before,
+      [:rescue, LocalJumpError],
+      :end_sync,
+      [:result, [false, nil, LocalJumpError]]]
+
+    assert_equal(expected, @log, bug18649)
+    assert_equal(42, value, bug18649)
+  end
+
   def test_thread_setname_in_initialize
     bug12290 = '[ruby-core:74963] [Bug #12290]'
     c = Class.new(Thread) {def initialize() self.name = "foo"; super; end}
diff --git a/vm.c b/vm.c
index b8df0d6ee5..f5016f6dec 100644
--- a/vm.c
+++ b/vm.c
@@ -1806,11 +1806,9 @@ vm_iter_break(rb_execution_context_t *ec, VALUE val)
     const VALUE *ep = VM_CF_PREV_EP(cfp);
     const rb_control_frame_t *target_cfp = rb_vm_search_cf_from_ep(ec, cfp, ep);
 
-#if 0				/* raise LocalJumpError */
     if (!target_cfp) {
 	rb_vm_localjump_error("unexpected break", val, TAG_BREAK);
     }
-#endif
 
     ec->errinfo = (VALUE)THROW_DATA_NEW(val, target_cfp, TAG_BREAK);
     EC_JUMP_TAG(ec, TAG_BREAK);