child_process: exec's promisify impl now includes stdout/err in error

doc/api/child_process.md

@@ -215,7 +215,9 @@ child runs longer than `timeout` milliseconds.
 replace the existing process and uses a shell to execute the command.
 
 If this method is invoked as its [`util.promisify()`][]ed version, it returns
-a Promise for an object with `stdout` and `stderr` properties.
+a Promise for an object with `stdout` and `stderr` properties. In case of an
+error, a rejected promise is returned, with the same `error` object given in the
+callback, but with an additional two properties `stdout` and `stderr`.
 
 For example:
 
@@ -281,7 +283,9 @@ stderr output. If `encoding` is `'buffer'`, or an unrecognized character
 encoding, `Buffer` objects will be passed to the callback instead.
 
 If this method is invoked as its [`util.promisify()`][]ed version, it returns
-a Promise for an object with `stdout` and `stderr` properties.
+a Promise for an object with `stdout` and `stderr` properties. In case of an
+error, a rejected promise is returned, with the same `error` object given in the
+callback, but with an additional two properties `stdout` and `stderr`.
 
 ```js
 const util = require('util');

lib/child_process.js

@@ -22,9 +22,9 @@
 'use strict';
 
 const util = require('util');
-const {
-  deprecate, convertToValidSignal, customPromisifyArgs
-} = require('internal/util');
+const { deprecate, convertToValidSignal } = require('internal/util');
+const { createPromise,
+  promiseResolve, promiseReject } = process.binding('util');
 const debug = util.debuglog('child_process');
 
 const uv = process.binding('uv');
@@ -140,9 +140,27 @@ exports.exec = function(command /*, options, callback*/) {
                           opts.callback);
 };
 
-Object.defineProperty(exports.exec, customPromisifyArgs,
-                      { value: ['stdout', 'stderr'], enumerable: false });
+const customPromiseExecFunction = (orig) => {
+  return (...args) => {
+    const promise = createPromise();
 
+    orig(...args, (err, stdout, stderr) => {
+      if (err !== null) {
+        err.stdout = stdout;
+        err.stderr = stderr;
+        promiseReject(promise, err);
+      } else {
+        promiseResolve(promise, { stdout, stderr });
+      }
+    });
+    return promise;
+  };
+};
+
+Object.defineProperty(exports.exec, util.promisify.custom, {
+  enumerable: false,
+  value: customPromiseExecFunction(exports.exec)
+});
 
 exports.execFile = function(file /*, args, options, callback*/) {
   var args = [];
@@ -338,8 +356,10 @@ exports.execFile = function(file /*, args, options, callback*/) {
   return child;
 };
 
-Object.defineProperty(exports.execFile, customPromisifyArgs,
-                      { value: ['stdout', 'stderr'], enumerable: false });
+Object.defineProperty(exports.execFile, util.promisify.custom, {
+  enumerable: false,
+  value: customPromiseExecFunction(exports.execFile)
+});
 
 const _deprecatedCustomFds = deprecate(
   function deprecateCustomFds(options) {

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

@@ -32,3 +32,22 @@ const execFile = promisify(child_process.execFile);
     assert(err.message.includes('doesntexist'));
   }));
 }
+const failingCodeWithStdoutErr =
+  'console.log(42);console.error(43);process.exit(1)';
+{
+  exec(`${process.execPath} -e "${failingCodeWithStdoutErr}"`)
+    .catch(common.mustCall((err) => {
+      assert.strictEqual(err.code, 1);
+      assert.strictEqual(err.stdout, '42\n');
+      assert.strictEqual(err.stderr, '43\n');
+    }));
+}
+
+{
+  execFile(process.execPath, ['-e', failingCodeWithStdoutErr])
+    .catch(common.mustCall((err) => {
+      assert.strictEqual(err.code, 1);
+      assert.strictEqual(err.stdout, '42\n');
+      assert.strictEqual(err.stderr, '43\n');
+    }));
+}