events: show throw stack trace for uncaught exception

Show the stack trace for the `eventemitter.emit('error')` call
in the case of an uncaught exception.

Previously, there would be no clue in Node’s output about where
the actual `throw` comes from.

PR-URL: https://github.com/nodejs/node/pull/19003
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

7 files changed, 108 insertions, 0 deletions

diff --git a/test/message/events_unhandled_error_common_trace.js b/test/message/events_unhandled_error_common_trace.js
new file mode 100644
index 0000000000..e6c168fc06
--- /dev/null
+++ b/test/message/events_unhandled_error_common_trace.js
@@ -0,0 +1,20 @@
+'use strict';
+require('../common');
+const EventEmitter = require('events');
+
+function foo() {
+  function bar() {
+    return new Error('foo:bar');
+  }
+
+  return bar();
+}
+
+const ee = new EventEmitter();
+const err = foo();
+
+function quux() {
+  ee.emit('error', err);
+}
+
+quux();
diff --git a/test/message/events_unhandled_error_common_trace.out b/test/message/events_unhandled_error_common_trace.out
new file mode 100644
index 0000000000..d39a95cb77
--- /dev/null
+++ b/test/message/events_unhandled_error_common_trace.out
@@ -0,0 +1,22 @@
+events.js:*
+      throw er; // Unhandled 'error' event
+      ^
+
+Error: foo:bar
+    at bar (*events_unhandled_error_common_trace.js:*:*)
+    at foo (*events_unhandled_error_common_trace.js:*:*)
+    at Object.<anonymous> (*events_unhandled_error_common_trace.js:*:*)
+    at Module._compile (module.js:*:*)
+    at Object.Module._extensions..js (module.js:*:*)
+    at Module.load (module.js:*:*)
+    at tryModuleLoad (module.js:*:*)
+    at Function.Module._load (module.js:*:*)
+    at Function.Module.runMain (module.js:*:*)
+    at startup (bootstrap_node.js:*:*)
+Emitted 'error' event at:
+    at quux (*events_unhandled_error_common_trace.js:*:*)
+    at Object.<anonymous> (*events_unhandled_error_common_trace.js:*:*)
+    at Module._compile (module.js:*:*)
+    [... lines matching original stack trace ...]
+    at startup (bootstrap_node.js:*:*)
+    at bootstrap_node.js:*:*
diff --git a/test/message/events_unhandled_error_nexttick.js b/test/message/events_unhandled_error_nexttick.js
new file mode 100644
index 0000000000..713031eeef
--- /dev/null
+++ b/test/message/events_unhandled_error_nexttick.js
@@ -0,0 +1,7 @@
+'use strict';
+require('../common');
+const EventEmitter = require('events');
+const er = new Error();
+process.nextTick(() => {
+  new EventEmitter().emit('error', er);
+});
diff --git a/test/message/events_unhandled_error_nexttick.out b/test/message/events_unhandled_error_nexttick.out
new file mode 100644
index 0000000000..f0591610ff
--- /dev/null
+++ b/test/message/events_unhandled_error_nexttick.out
@@ -0,0 +1,20 @@
+events.js:*
+      throw er; // Unhandled 'error' event
+      ^
+
+Error
+    at Object.<anonymous> (*events_unhandled_error_nexttick.js:*:*)
+    at Module._compile (module.js:*:*)
+    at Object.Module._extensions..js (module.js:*:*)
+    at Module.load (module.js:*:*)
+    at tryModuleLoad (module.js:*:*)
+    at Function.Module._load (module.js:*:*)
+    at Function.Module.runMain (module.js:*:*)
+    at startup (bootstrap_node.js:*:*)
+    at bootstrap_node.js:*:*
+Emitted 'error' event at:
+    at process.nextTick (*events_unhandled_error_nexttick.js:*:*)
+    at process._tickCallback (internal/process/next_tick.js:*:*)
+    at Function.Module.runMain (module.js:*:*)
+    at startup (bootstrap_node.js:*:*)
+    at bootstrap_node.js:*:*
diff --git a/test/message/events_unhandled_error_sameline.js b/test/message/events_unhandled_error_sameline.js
new file mode 100644
index 0000000000..1e5e77d08c
--- /dev/null
+++ b/test/message/events_unhandled_error_sameline.js
@@ -0,0 +1,4 @@
+'use strict';
+require('../common');
+const EventEmitter = require('events');
+new EventEmitter().emit('error', new Error());
diff --git a/test/message/events_unhandled_error_sameline.out b/test/message/events_unhandled_error_sameline.out
new file mode 100644
index 0000000000..100c294276
--- /dev/null
+++ b/test/message/events_unhandled_error_sameline.out
@@ -0,0 +1,19 @@
+events.js:*
+      throw er; // Unhandled 'error' event
+      ^
+
+Error
+    at Object.<anonymous> (*events_unhandled_error_sameline.js:*:*)
+    at Module._compile (module.js:*:*)
+    at Object.Module._extensions..js (module.js:*:*)
+    at Module.load (module.js:*:*)
+    at tryModuleLoad (module.js:*:*)
+    at Function.Module._load (module.js:*:*)
+    at Function.Module.runMain (module.js:*:*)
+    at startup (bootstrap_node.js:*:*)
+    at bootstrap_node.js:*:*
+Emitted 'error' event at:
+    at Object.<anonymous> (*events_unhandled_error_sameline.js:*:*)
+    at Module._compile (module.js:*:*)
+    [... lines matching original stack trace ...]
+    at bootstrap_node.js:*:*
diff --git a/test/parallel/test-events-uncaught-exception-stack.js b/test/parallel/test-events-uncaught-exception-stack.js
new file mode 100644
index 0000000000..c55322a5aa
--- /dev/null
+++ b/test/parallel/test-events-uncaught-exception-stack.js
@@ -0,0 +1,16 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const EventEmitter = require('events');
+
+// Tests that the error stack where the exception was thrown is *not* appended.
+
+process.on('uncaughtException', common.mustCall((err) => {
+  const lines = err.stack.split('\n');
+  assert.strictEqual(lines[0], 'Error');
+  lines.slice(1).forEach((line) => {
+    assert(/^    at/.test(line), `${line} has an unexpected format`);
+  });
+}));
+
+new EventEmitter().emit('error', new Error());