child_process: promisify includes stdio in error

This converts the initial implementation of a promised exec that used
the customPromisifyArgs support in util.promisify with a custom
implementation. This is because exec and execFile, when there is an
error, still supply the stdout and stderr of the process, and yet
the promisified version with customPromisifyArgs does
not supply this ability.

I created a custom implementation and attached it to exec and execFile
using the util.promisify.custom key.

Fixes: #13364
PR-URL: #13388
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

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');
+    }));
+}