Move Babel transforms to the main process.

[jamestalmage]

This moves Babel transforms to the main process, and caches the transpiled results.

It uses caching-transform to provide caching. Expensive requires (like babel) are placed inside the factory function, which caching-transform only calls when it determines it needs to transform a file.

The path to each precompiled test is passed in the options object to fork:

fork('/path/to/file.js', {
  precompiled: {
    '/path/to/file.js': '/path/to/cached/file.js'
  }
});

It uses require-precompiled to install a require hook that pulls the transformed file from the cache.

The caching directory is used by the users package.json, and installing in node_modules/.cache/ava.
If the cache directory cannot be found (i.e. if they have no package.json), or the user provides a --no-cache flag, pre-compilation still happens on the main thread - but results are published to a temp directory.

---

Speedup is dramatic.
Using the 6.0.0 branch of got:

ava master branch

$ time ava
# npm 2
ava  85.51s user 7.19s system 592% cpu 15.650 total
# npm 3
ava  24.87s user 1.91s system 384% cpu 6.957 total

this branch using --no-cache

$ time ava --no-cache
# npm 2
ava --no-cache  11.19s user 1.05s system 130% cpu 9.379 total
# npm 3
ava --no-cache  7.59s user 0.75s system 134% cpu 6.217 total

This branch with caching enabled

$ time ava
# npm 2
ava  7.86s user 0.81s system 193% cpu 4.484 total
# npm 3
ava  6.64s user 0.72s system 173% cpu 4.237 total

A couple points of interest here:

• This drastically reduces the penalty for sticking with npm 2 even on your first run.
• You absolutely should upgrade to npm 3 for the best performance.

[vadimdemedes]

Rebase went wrong here.

[jamestalmage]

Rebase went wrong here.

It wasn't like that last night.

[sindresorhus]

Use https://github.com/sindresorhus/del-cli to make it work on Windwos too.

[jamestalmage]

OK, I tried trash-cli first but it fails if the directory doesn't exist. Was just about to push rimraf, does del-cli accept missing directories?

[sindresorhus]

@jamestalmage Re trash-cli, that's a bug sindresorhus/trash#43, but no point in having the overhead of moving it to the trash, not something you'd ever care about restoring.

[jamestalmage]

@sindresorhus I used rimraf over del-cli, because sindresorhus/del-cli#3

[jamestalmage]

Hmm, it seems implementing caching fixed my Windows errors. I previously saw some errors that made me suspicious the problem was in temp-write. I'm even more suspicious now.

[sindresorhus]

@jamestalmage del-cli now supports Node.js 0.10.

[jamestalmage]

OK, cool.
I'm heading out for ~4 hours. I will apply all the suggested changes later tonight.

[jamestalmage]

OK, This is ready for review.

// @vdemedes @sindresorhus

[sindresorhus]

noCache => cache. I don't like double negatives.

[sindresorhus]

This could use https://github.com/sindresorhus/md5-hex now.

[jamestalmage]

closed in favor of #390