process: Change default --unhandled-rejections=warn-with-error-code

This is a semver-major change that resolves DEP0018.

In addition to changing the default value for --unhandled-rejections,
this PR changes the exit code from 1 to 66. The warning message has
been updated to mention the new exit code, which I selected in order
to make this problem easier to search for on the web.

Users can prevent this behavior by setting a non-default value for the
--unhandled-rejections flag (throw, strict, warn, or none) or by setting
a hook for 'unhandledRejection'. This change has no effect on users who
have already set the flag or installed an 'unhandledRejection' hook; it
will only impact users who currently see a DEP0018 warning today.

Author: dfabulich

doc/api/cli.md

@@ -978,20 +978,17 @@ added:
  - v10.17.0
 -->
 
-By default all unhandled rejections trigger a warning plus a deprecation warning
-for the very first unhandled rejection in case no [`unhandledRejection`][] hook
-is used.
-
 Using this flag allows to change what should happen when an unhandled rejection
 occurs. One of the following modes can be chosen:
 
+* `warn-with-error-code`: Emit [`unhandledRejection`][]. If this hook is not
+  set, trigger a warning, and set the process exit code to 66. This is the
+  default.
 * `throw`: Emit [`unhandledRejection`][]. If this hook is not set, raise the
   unhandled rejection as an uncaught exception.
 * `strict`: Raise the unhandled rejection as an uncaught exception.
 * `warn`: Always trigger a warning, no matter if the [`unhandledRejection`][]
   hook is set or not but do not print the deprecation warning.
-* `warn-with-error-code`: Emit [`unhandledRejection`][]. If this hook is not
-  set, trigger a warning, and set the process exit code to 1.
 * `none`: Silence all warnings.
 
 ### `--use-bundled-ca`, `--use-openssl-ca`

lib/internal/process/promises.js

@@ -53,14 +53,11 @@ const kThrowUnhandledRejections = 3;
 
 // --unhandled-rejections=warn-with-error-code:
 // Emit 'unhandledRejection', if it's unhandled, emit
-// 'UnhandledPromiseRejectionWarning', then set process exit code to 1.
+// 'UnhandledPromiseRejectionWarning', then set process exit code to 66.
 
 const kWarnWithErrorCodeUnhandledRejections = 4;
 
-// --unhandled-rejections is unset:
-// Emit 'unhandledRejection', if it's unhandled, emit
-// 'UnhandledPromiseRejectionWarning', then emit deprecation warning.
-const kDefaultUnhandledRejections = 5;
+const unhandledRejectionExitCode = 66;
 
 let unhandledRejectionsMode;
 
@@ -86,7 +83,7 @@ function getUnhandledRejectionsMode() {
     case 'warn-with-error-code':
       return kWarnWithErrorCodeUnhandledRejections;
     default:
-      return kDefaultUnhandledRejections;
+      return kWarnWithErrorCodeUnhandledRejections;
   }
 }
 
@@ -151,12 +148,14 @@ function handledRejection(promise) {
 }
 
 const unhandledRejectionErrName = 'UnhandledPromiseRejectionWarning';
-function emitUnhandledRejectionWarning(uid, reason) {
+function emitUnhandledRejectionWarning(uid, reason, failing) {
   const warning = getErrorWithoutStack(
     unhandledRejectionErrName,
     'Unhandled promise rejection. This error originated either by ' +
       'throwing inside of an async function without a catch block, ' +
       'or by rejecting a promise which was not handled with .catch(). ' +
+      (failing ? 'This process will terminate with exit code ' +
+        unhandledRejectionExitCode + '. ' : '') +
       'To terminate the node process on unhandled promise ' +
       'rejection, use the CLI flag `--unhandled-rejections=strict` (see ' +
       'https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). ' +
@@ -175,15 +174,6 @@ function emitUnhandledRejectionWarning(uid, reason) {
   process.emitWarning(warning);
 }
 
-let deprecationWarned = false;
-function emitDeprecationWarning() {
-  process.emitWarning(
-    'Unhandled promise rejections are deprecated. In the future, ' +
-    'promise rejections that are not handled will terminate the ' +
-    'Node.js process with a non-zero exit code.',
-    'DeprecationWarning', 'DEP0018');
-}
-
 // If this method returns true, we've executed user code or triggered
 // a warning to be emitted which requires the microtask and next tick
 // queues to be drained again.
@@ -236,19 +226,8 @@ function processPromiseRejections() {
       case kWarnWithErrorCodeUnhandledRejections: {
         const handled = process.emit('unhandledRejection', reason, promise);
         if (!handled) {
-          emitUnhandledRejectionWarning(uid, reason);
-          process.exitCode = 1;
-        }
-        break;
-      }
-      case kDefaultUnhandledRejections: {
-        const handled = process.emit('unhandledRejection', reason, promise);
-        if (!handled) {
-          emitUnhandledRejectionWarning(uid, reason);
-          if (!deprecationWarned) {
-            emitDeprecationWarning();
-            deprecationWarned = true;
-          }
+          emitUnhandledRejectionWarning(uid, reason, true /* failing */);
+          process.exitCode = unhandledRejectionExitCode;
         }
         break;
       }

test/es-module/test-esm-cjs-load-error-note.mjs

@@ -17,6 +17,7 @@ const expectedNote = 'To load an ES module, ' +
 'or use the .mjs extension.';
 
 const expectedCode = 1;
+const expectedUnhandledRejectionCode = 66;
 
 const pExport1 = spawn(process.execPath, [Export1]);
 let pExport1Stderr = '';
@@ -63,8 +64,7 @@ pImport2.stderr.on('data', (data) => {
   pImport2Stderr += data;
 });
 pImport2.on('close', mustCall((code) => {
-  // As this exits normally we expect 0
-  assert.strictEqual(code, 0);
+  assert.strictEqual(code, expectedUnhandledRejectionCode);
   assert.ok(!pImport2Stderr.includes(expectedNote),
             `${expectedNote} must not be included in ${pImport2Stderr}`);
 }));
@@ -94,15 +94,15 @@ pImport4.on('close', mustCall((code) => {
             `${expectedNote} not found in ${pImport4Stderr}`);
 }));
 
-// Must exit with zero and show note
+// Must exit with 66 and show note
 const pImport5 = spawn(process.execPath, [Import5]);
 let pImport5Stderr = '';
 pImport5.stderr.setEncoding('utf8');
 pImport5.stderr.on('data', (data) => {
   pImport5Stderr += data;
 });
 pImport5.on('close', mustCall((code) => {
-  assert.strictEqual(code, 0);
+  assert.strictEqual(code, expectedUnhandledRejectionCode);
   assert.ok(!pImport5Stderr.includes(expectedNote),
             `${expectedNote} must not be included in ${pImport5Stderr}`);
 }));

test/message/promise_unhandled_warn_with_error.js

@@ -7,4 +7,4 @@ const assert = require('assert');
 common.disableCrashOnUnhandledRejection();
 
 Promise.reject(new Error('alas'));
-process.on('exit', assert.strictEqual.bind(null, 1));
+process.on('exit', assert.strictEqual.bind(null, 66));

test/message/promise_unhandled_warn_with_error.out

@@ -7,4 +7,4 @@
     at *
     at *
 (Use `node --trace-warnings ...` to show where the warning was created)
-*UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
+*UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). This process will terminate with exit code 66. To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)

test/message/unhandled_promise_trace_warnings.out

@@ -17,10 +17,6 @@
     at *
     at *
     at *
-(node:*) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
-    at *
-    at *
-    at *
 (node:*) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 1)
     at handledRejection (internal/process/promises.js:*)
     at promiseRejectHandler (internal/process/promises.js:*)

test/parallel/test-async-wrap-pop-id-during-load.js

@@ -19,7 +19,7 @@ const ret = spawnSync(
   ['--stack_size=150', __filename, 'async'],
   { maxBuffer: Infinity }
 );
-assert.strictEqual(ret.status, 0,
+assert.strictEqual(ret.status, 66,
                    `EXIT CODE: ${ret.status}, STDERR:\n${ret.stderr}`);
 const stderr = ret.stderr.toString('utf8', 0, 2048);
 assert.ok(!/async.*hook/i.test(stderr));

test/parallel/test-promises-unhandled-proxy-rejections.js

@@ -1,13 +1,9 @@
+// Flags: --unhandled-rejections=warn
 'use strict';
 const common = require('../common');
 
 common.disableCrashOnUnhandledRejection();
 
-const expectedDeprecationWarning = ['Unhandled promise rejections are ' +
-                                   'deprecated. In the future, promise ' +
-                                   'rejections that are not handled will ' +
-                                   'terminate the Node.js process with a ' +
-                                   'non-zero exit code.', 'DEP0018'];
 const expectedPromiseWarning = ['Unhandled promise rejection. ' +
   'This error originated either by throwing ' +
   'inside of an async function without a catch ' +
@@ -39,7 +35,6 @@ const thorny = new Proxy({}, {
 });
 
 common.expectWarning({
-  DeprecationWarning: expectedDeprecationWarning,
   UnhandledPromiseRejectionWarning: expectedPromiseWarning,
 });
 

test/parallel/test-promises-unhandled-rejections.js

@@ -1,3 +1,4 @@
+// Flags: --unhandled-rejections=warn
 'use strict';
 const common = require('../common');
 const assert = require('assert');
@@ -714,7 +715,7 @@ asyncTest(
         done();
       }
       emitWarning(...args);
-    }, 2);
+    }, 4);
 
     let timer = setTimeout(common.mustNotCall(), 10000);
   },

test/parallel/test-promises-unhandled-symbol-rejections.js

@@ -1,14 +1,10 @@
+// Flags: --unhandled-rejections=warn
 'use strict';
 const common = require('../common');
 
 common.disableCrashOnUnhandledRejection();
 
 const expectedValueWarning = ['Symbol()'];
-const expectedDeprecationWarning = ['Unhandled promise rejections are ' +
-                                   'deprecated. In the future, promise ' +
-                                   'rejections that are not handled will ' +
-                                   'terminate the Node.js process with a ' +
-                                   'non-zero exit code.', 'DEP0018'];
 const expectedPromiseWarning = ['Unhandled promise rejection. ' +
   'This error originated either by throwing ' +
   'inside of an async function without a catch ' +
@@ -20,7 +16,6 @@ const expectedPromiseWarning = ['Unhandled promise rejection. ' +
   '(rejection id: 1)'];
 
 common.expectWarning({
-  DeprecationWarning: expectedDeprecationWarning,
   UnhandledPromiseRejectionWarning: [
     expectedValueWarning,
     expectedPromiseWarning