src: print exceptions from PromiseRejectCallback

Previously, leaving the exception lying around would leave the JS
engine in an invalid state, as it was not expecting exceptions to
be thrown from the C++ `PromiseRejectCallback`, and lead to hard
crashes under some conditions (e.g. with coverage enabled).

PR-URL: https://github.com/nodejs/node/pull/29513
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/node_task_queue.cc b/src/node_task_queue.cc
index 4ff51bc3b80..b4e8c1de928 100644
--- a/src/node_task_queue.cc
+++ b/src/node_task_queue.cc
@@ -10,6 +10,7 @@
 
 namespace node {
 
+using errors::TryCatchScope;
 using v8::Array;
 using v8::Context;
 using v8::Function;
@@ -111,8 +112,17 @@ void PromiseRejectCallback(PromiseRejectMessage message) {
   }
 
   Local<Value> args[] = { type, promise, value };
+
+  // V8 does not expect this callback to have a scheduled exceptions once it
+  // returns, so we print them out in a best effort to do something about it
+  // without failing silently and without crashing the process.
+  TryCatchScope try_catch(env);
   USE(callback->Call(
       env->context(), Undefined(isolate), arraysize(args), args));
+  if (try_catch.HasCaught() && !try_catch.HasTerminated()) {
+    fprintf(stderr, "Exception in PromiseRejectCallback:\n");
+    PrintCaughtException(isolate, env->context(), try_catch);
+  }
 }
 
 static void SetPromiseRejectCallback(