`rb_fiber_terminate` must not return [Bug #18497]

In a forked process from a fiber, the fiber becomes the only
fiber, `fiber_switch` does nothing as there is no other fibers,
`rb_fiber_terminate` does not terminate the fiber.  In that case,
reaches the end of `fiber_entry` finaly, which is declared as
"COROUTINE" and should never return.

1 files changed, 2 insertions, 1 deletions

diff --git a/cont.c b/cont.c
index 96654733f8..f9ebb4483e 100644
--- a/cont.c
+++ b/cont.c
@@ -2039,7 +2039,7 @@ rb_fiber_set_scheduler(VALUE klass, VALUE scheduler)
     return rb_fiber_scheduler_set(scheduler);
 }
 
-static void rb_fiber_terminate(rb_fiber_t *fiber, int need_interrupt, VALUE err);
+NORETURN(static void rb_fiber_terminate(rb_fiber_t *fiber, int need_interrupt, VALUE err));
 
 void
 rb_fiber_start(rb_fiber_t *fiber)
@@ -2408,6 +2408,7 @@ rb_fiber_terminate(rb_fiber_t *fiber, int need_interrupt, VALUE error)
         fiber_switch(next_fiber, -1, &error, RB_NO_KEYWORDS, NULL, false);
     else
         fiber_switch(next_fiber, 1, &value, RB_NO_KEYWORDS, NULL, false);
+    ruby_stop(0);
 }
 
 static VALUE