stricter check for double resume; close #1885

mrbgems/mruby-fiber/src/fiber.c

@@ -164,7 +164,7 @@ fiber_resume(mrb_state *mrb, mrb_value self)
       mrb_raise(mrb, E_ARGUMENT_ERROR, "can't cross C function boundary");
     }
   }
-  if (c->status == MRB_FIBER_RUNNING) {
+  if (c->status == MRB_FIBER_RUNNING || (mrb->c->prev && mrb->c->prev != mrb->root_c)) {
     mrb_raise(mrb, E_RUNTIME_ERROR, "double resume");
   }
   if (c->status == MRB_FIBER_TERMINATED) {

mrbgems/mruby-fiber/test/fiber.rb

@@ -88,3 +88,16 @@ assert('Double resume of Fiber') do
   assert_false f1.alive?
   assert_false f2.alive?
 end
+
+assert('Recursive resume of Fiber') do
+  f1, f2 = nil, nil
+  f1 = Fiber.new { assert_raise(RuntimeError) { f2.resume } }
+  f2 = Fiber.new {
+    f1.resume
+    Fiber.yield 0
+  }
+  assert_equal 0, f2.resume
+  f2.resume
+  assert_false f1.alive?
+  assert_false f2.alive?
+end