fix typescript compiler emit output

[HerringtonDarkholme]

Syntastic will emit js file when checking TypeScript file. This is not a desirable behavior.

According to TypeScript module specs, --out flags should not be used with external module. So --module commonjs and --out /dev/null are two mutually exclusiv arguments.

This is not a problem with TypeScript compiler, because module loader specs require all files are separated and imported by loader. So --output is not a valid option for checking.

However, tsc does provide a more straightforward option --noEmit, which is a more sensible alternative.
This also fixes #1155

[lcd047]

However, tsc does provide a more straightforward option --noEmit

Except this option is new in tsc 1.5.0-alpha, so your patch is missing at least a version check.

Other than lack of conceptual purity, is there any downside to mixing --module commonjs with --out /dev/null when checking syntax, for versions 1.4 and earlier?

This also fixes #1155

It fixes the reported behaviour, not the root of the problem. The root of the problem, as I pointed out, is in libuv, and it also affects other syntastic checkers.

[HerringtonDarkholme]

Or I will add a version check, with TS1.5 --noEmit and other version as --out /dev/null.

Using --module commonjs just ignores --out /dev/null, and all js files get emitted.

[HerringtonDarkholme]

I don't think there is an optimal solution for now. TS Vim user should find their own way to get rid of this.

[lcd047]

--out /dev/null is not ignored with tsc 1.4 and earlier. It seems to work as intended on all systems except Windows, where it fails for the reason mentioned in #1155.

[lcd047]

Please see fe43637.