child_process: Pass child in resolve/reject too

doc/api/child_process.md

@@ -209,8 +209,7 @@ encoding, `Buffer` objects will be passed to the callback instead.
 const { exec } = require('child_process');
 exec('cat *.js missing_file | wc -l', (error, stdout, stderr) => {
   if (error) {
-    console.error(`exec error: ${error}`);
-    return;
+    console.error(`exit(${error.code}): ${error}`);
   }
   console.log(`stdout: ${stdout}`);
   console.error(`stderr: ${stderr}`);
@@ -224,6 +223,8 @@ child runs longer than `timeout` milliseconds.
 Unlike the exec(3) POSIX system call, `child_process.exec()` does not replace
 the existing process and uses a shell to execute the command.
 
+#### exec with promisify
+
 If this method is invoked as its [`util.promisify()`][]ed version, it returns
 a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned
 `ChildProcess` instance is attached to the `Promise` as a `child` property. In
@@ -306,19 +307,34 @@ can be used to specify the character encoding used to decode the stdout and
 stderr output. If `encoding` is `'buffer'`, or an unrecognized character
 encoding, `Buffer` objects will be passed to the callback instead.
 
+#### execFile with promisify
+
 If this method is invoked as its [`util.promisify()`][]ed version, it returns
-a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned
-`ChildProcess` instance is attached to the `Promise` as a `child` property. In
-case of an error (including any error resulting in an exit code other than 0), a
-rejected promise is returned, with the same `error` object given in the
-callback, but with two additional properties `stdout` and `stderr`.
+a `Promise`, with an additional property `child` with the `ChildProcess` that
+would normally be returned by `execFile`.
+
+On a successful exit (a zero status code), the promise resolves to an object
+with `child`, `stdout`, and `stderr` properties.
+
+On an unsuccessful exit, the promise resolves to the same `error` returned in
+the callback, with three additional properties `child`, `stdout`, `stderr`,
+which provide the output of the process. As with `exec`, the exit code is
+attached to the `code` property.
 
 ```js
-const util = require('util');
-const execFile = util.promisify(require('child_process').execFile);
+const { promisify } = require('util');
+const execFile = promisify(require('child_process').execFile);
 async function getVersion() {
-  const { stdout } = await execFile('node', ['--version']);
-  console.log(stdout);
+  try {
+    const { stdout, stderr, child } = await execFile('node', ['--version']);
+    console.log(`pid ${child.pid} exit`);
+    console.log(`stdout: ${stdout}`);
+    console.error(`stderr: ${stderr}`);
+  } catch (error) {
+    console.error(`pid ${error.child.pid} exit(${error.code}): ${error}`);
+    console.log(`stdout: ${error.stdout}`);
+    console.error(`stderr: ${error.stderr}`);
+  }
 }
 getVersion();
 ```

lib/child_process.js

@@ -169,13 +169,14 @@ const customPromiseExecFunction = (orig) => {
       reject = rej;
     });
 
-    promise.child = orig(...args, (err, stdout, stderr) => {
+    const child = promise.child = orig(...args, (err, stdout, stderr) => {
       if (err !== null) {
+        err.child = child;
         err.stdout = stdout;
         err.stderr = stderr;
         reject(err);
       } else {
-        resolve({ stdout, stderr });
+        resolve({ child, stdout, stderr });
       }
     });
 

test/parallel/test-child-process-promisified.js

@@ -12,7 +12,9 @@ const execFile = promisify(child_process.execFile);
 
   assert(promise.child instanceof child_process.ChildProcess);
   promise.then(common.mustCall((obj) => {
-    assert.deepStrictEqual(obj, { stdout: '42\n', stderr: '' });
+    assert(obj.child instanceof child_process.ChildProcess);
+    assert.strictEqual(obj.stdout, '42\n');
+    assert.strictEqual(obj.stderr, '');
   }));
 }
 
@@ -21,7 +23,9 @@ const execFile = promisify(child_process.execFile);
 
   assert(promise.child instanceof child_process.ChildProcess);
   promise.then(common.mustCall((obj) => {
-    assert.deepStrictEqual(obj, { stdout: '42\n', stderr: '' });
+    assert(obj.child instanceof child_process.ChildProcess);
+    assert.strictEqual(obj.stdout, '42\n');
+    assert.strictEqual(obj.stderr, '');
   }));
 }
 
@@ -31,6 +35,7 @@ const execFile = promisify(child_process.execFile);
   assert(promise.child instanceof child_process.ChildProcess);
   promise.catch(common.mustCall((err) => {
     assert(err.message.includes('doesntexist'));
+    assert(err.child instanceof child_process.ChildProcess);
   }));
 }
 
@@ -40,13 +45,15 @@ const execFile = promisify(child_process.execFile);
   assert(promise.child instanceof child_process.ChildProcess);
   promise.catch(common.mustCall((err) => {
     assert(err.message.includes('doesntexist'));
+    assert(err.child instanceof child_process.ChildProcess);
   }));
 }
 const failingCodeWithStdoutErr =
   'console.log(42);console.error(43);process.exit(1)';
 {
   exec(`${process.execPath} -e "${failingCodeWithStdoutErr}"`)
     .catch(common.mustCall((err) => {
+      assert(err.child instanceof child_process.ChildProcess);
       assert.strictEqual(err.code, 1);
       assert.strictEqual(err.stdout, '42\n');
       assert.strictEqual(err.stderr, '43\n');
@@ -56,6 +63,7 @@ const failingCodeWithStdoutErr =
 {
   execFile(process.execPath, ['-e', failingCodeWithStdoutErr])
     .catch(common.mustCall((err) => {
+      assert(err.child instanceof child_process.ChildProcess);
       assert.strictEqual(err.code, 1);
       assert.strictEqual(err.stdout, '42\n');
       assert.strictEqual(err.stderr, '43\n');