Asset relocations

[guybedford]

This implements #17 emitting assets as separate files.

It is based to the sourcemap branch as I was using that for debugging, but we can always rebase to master too.

It's a bit of a trick, which I'm not sure if anything else does, which is basically to detect references to __dirname or __filename then to statically analyze outward from those to see if it ends up forming a statically analyzable string literal to a known file path. In the process it will support path functions etc in this computation thanks to the browserify fs static-eval lib.

If it does find a file, it emits it as an asset of the build and relocates that static expression to reference the build output asset folder. So it's almost slightly lower level than the brfs approach in that we don't even need to analyze if there was an fs.readFile etc.

This implements #17, and fixes #2 as well as the saslprep bug.

The grpc bug in #33 is still failing unfortunately the issue is that we have:

var binding_path =
    binary.find(path.resolve(path.join(__dirname, '../package.json')));

being successfully rewritten by this loader into:

var binding_path =
    binary.find(__dirname + "/assets/package.json");

but the issue is that binding_path is then passed to require(binding_path) where Webpack will then rewrite that require to its own require, which throws during runtime.

One hack might even be to rewrite the runtime webpack require to fallback to using the local require instead of failing outright... will see if I can implement something along those lines tomorrow.

[guybedford]

Note this is currently failing the self-build as webpack loaders aren't currently supported by ncc itself.

Currently looking into options.

[guybedford]

The first flaw in this approach was that we don't want to emit "js" files as assets, which this trick would naturally do. The reason for this is that we might then be requireing an unbuilt file, with all its local requires etc... which wouldn't work.

I've just added a fix such that we only emit assets when the static file is not a ".js" or ".mjs" file, leaving those fully to webpack to handle.

[guybedford]

I finally got the self-build running again here.

The final approach was to build the asset-relocator.js file separately in the build script, and then ensure that the webpack_require within the build output will always fallback to the Node require in the build before throwing a not found error by hooking into the context module output.