Avoid empty error messages

[pelotom]

This fixes a problem where psc and docgen throw errors while throwing errors. That is, if a compilation error occurs during psc for example, we emit an error using new gutil.PluginError(PLUGIN, buffer.toString()), but buffer.toString() is null, so we get this error:

Error: Missing error message
    at new PluginError (/Users/tom/code/purescript-d3-examples/node_modules/gulp-purescript/node_modules/gulp-util/lib/PluginError.js:53:28)
    at ChildProcess.<anonymous> (/Users/tom/code/purescript-d3-examples/node_modules/gulp-purescript/index.js:94:38)
    at ChildProcess.emit (events.js:98:17)
    at maybeClose (child_process.js:755:16)
    at Socket.<anonymous> (child_process.js:968:11)
    at Socket.emit (events.js:95:17)
    at Pipe.close (net.js:465:12)

which can't be handled and causes gulp to exit. This is especially annoying when trying to use gulp watch.

The fix makes psc and docgen do the same thing as pscMake; that is, give a static failure message.

[garyb]

Is it worth doing these as buffer.toString() || "psc has failed"? Or is the buffer always empty in this case?

[ethul]

@garyb I agree. I think we want to keep the buffer's value in these cases. Maybe we should go with your suggestion. Does this work for you @pelotom?

[pelotom]

In my experience it is always empty, but I'm certainly not opposed to showing it if there's ever something there.

[ethul]

@pelotom, can you please try out version 0.0.9? I think the issue was that the plugin needed to capture the buffer on stderr instead of stdout. I think in the newer version of purescript, the compiler error is no longer written to stdout, which resulted in the error you saw. I made the change and published it as 0.0.9. If this does not work for you, maybe we can look at this again and revisit this PR. Thanks for tracking down this issue!

[pelotom]

That works great, but shouldn't pscMake do the same? It's still spitting out a constant message 'psc-make has failed'.

[ethul]

Great, glad it works!

Regarding pscMake, that command actually works a little different. It does not do any streaming of files, it just outputs them to the filesystem directly. Since there is no buffer to collect on stdout, I just logged the error message on stderr, just like the stdout behaviour. I'd be open to collecting stderr in a buffer, but I could go either way.

[pelotom]

I think still collecting the stderr output and logging that when an error happens is better behavior. For one thing, stderr gets interleaved nondeterministically with other gulp output, so you get stuff like this:

[14:27:20] Stderr from 'psc'
"/Users/tom/code/pure
[14:27:20] Stderr from 'psc'
script-d3-examples/src/LetsMakeABarChart.purs" (line 33, column 3):
expecting indentation

That's from before your fix to psc. Now it looks like this:

[14:29:04] Error: "/Users/tom/code/purescript-d3-examples/src/LetsMakeABarChart.purs" (line 33, column 3):
expecting indentation

Much nicer.

[ethul]

That's a good point. I think it makes sense to collect stderr and stdout into buffers. I've opened issue #7 to track this.

Thanks!