Avoid assertion violation when comparing with main-thread

* src/thread.c (unmark_main_thread): New function.
* src/lisp.h (unmark_main_thread): Prototype it.
* src/alloc.c (garbage_collect_1): Call it after sweeping.
(Bug#33073)

* test/src/thread-tests.el (threads-test-bug33073): New test.

3 files changed, 9 insertions, 0 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 6aeac140ca0..1a72941cc92 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -6003,6 +6003,8 @@ garbage_collect_1 (void *end)
   VECTOR_UNMARK (&buffer_defaults);
   VECTOR_UNMARK (&buffer_local_symbols);
 
+  unmark_main_thread ();
+
   check_cons_list ();
 
   gc_in_progress = 0;
diff --git a/src/lisp.h b/src/lisp.h
index 782c396dbb4..24551699328 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3975,6 +3975,7 @@ extern void syms_of_module (void);
 
 /* Defined in thread.c.  */
 extern void mark_threads (void);
+extern void unmark_main_thread (void);
 
 /* Defined in editfns.c.  */
 extern void insert1 (Lisp_Object);
diff --git a/src/thread.c b/src/thread.c
index 0cd1ae33dc2..47f55e7f67c 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -656,6 +656,12 @@ mark_threads (void)
   flush_stack_call_func (mark_threads_callback, NULL);
 }
 
+void
+unmark_main_thread (void)
+{
+  main_thread.header.size &= ~ARRAY_MARK_FLAG;
+}
+
 
 
 static void