Improve usability of child process's stream interface for util.spawn

[jharding]

Right now, if the command passed to util.spawn isn't found, undefined is returned and the done callback is invoked. This makes it impossible to rely entirely on the stream interface of the spawned child process. For example, I couldn't do the following:

var child = grunt.spawn('notacommand');

child.stdout.on('data', function(d) { grunt.log.write(d); });
child.stderr.on('data', function(d) { grunt.log.error(d); });

Instead, I'd have to do something like:

var child = grunt.spawn('notacommand', function(error, result, code) {
  code !== 0 && grunt.log.error(result.stderr);
});

child && child.stdout.on('data', function(d) { grunt.log.write(d); });
child && child.stderr.on('data', function(d) { grunt.log.error(d); });

This pull request adds support for the former example. The downside to this change is that the error message for when a command is not found is not as descriptive as it previously was. If this is a sticking point for this pull request, I'll address the regression.

One other note – I didn't test this out on Windows.

[shama]

+1

[sindresorhus]

👍

[cowboy]

I'm hesitant to make this change, due to the fact that it could break existing code in a great number of projects and plugins.

[jharding]

So I guess the only "API" change I've made is that undefined no longer gets returned if node-which fails to find the command. Is that something you think a lot of projects depend on? I honestly haven no idea if it is or isn't.

[cowboy]

Well, I'm not sure. If someone is doing if (child) { ... } then it will definitely break their code.

[vladikoff]

Due to a breaking change we push it to 0.next, Tracking in gruntjs/grunt-next#2