Data URL support

[apellerano-pw]

There are certain situations where the user might prefer to completely inline their sourcemap rather than store it in an external file. For example, there's a longstanding Chrome bug where it can't load sourcemaps from the chrome-extension:// protocol, so you're forced to inline.

I made a proof of concept showing how this lib could add inline support via source-map.js:

// add this for inline support
if (this.someNewSwitch) {
  const dataUrlPrelude = 'data:application/json;charset=utf-8;base64,';
  const base64Content = Buffer.from(JSON.stringify(sourceMap.content)).toString('base64');
  sourceMap.mapURL = `${dataUrlPrelude}${base64Content}`;
}

// right before this existing code
if (sourceMap.mapCommentType === 'line') {
  stream.write('//# sourceMappingURL=' + sourceMap.mapURL + '\n');
} else {
  stream.write('/*# sourceMappingURL=' + sourceMap.mapURL + ' */\n');
}

Would this lib be open to an improvement like this? I'm not sure what the option switch(es) should be to toggle the behavior.

Also I'm unclear if this lib is meant to be standalone or if it's a microlib for ember-cli only. If the latter, what would it take to make this functionality controllable from ember-cli-build.js? They already support babel: { sourceMaps: 'inline' } but the intent isn't to do this, or it'd already be doing it. So it needs a new switch, with a different name to not interfere with existing use cases.

[apellerano-pw]

Here's a spec for what I'll write:

1. Add support for options.mayStyle which can be 'data' or 'file'. Defaults to 'file'.
2. If mapStyle is 'data', don't initialize mapFile. The existing code supports this and won't write the sourcemap file to disk.
3. Add an error check at the top of the ctor: if options.mapStyle is 'data', and either options.mapFile or options.mapURL are defined; this makes no sense.
4. Before writing the sourceMappingURL line: if mapStyle is 'data', construct a data URL like in my initial post and write that instead.

Now broccoli-concat can allow for a config like this to get the data URL behavior:

{
  sourceMapConfig: {
    enabled: true,
    mapStyle: 'data',
  }
}

No plan yet for how to get a config like that when all you can modify is ember-cli-build.js.

[apellerano-pw]

Ooh, looks like ember-cli already passes the sourcemaps hash defined in ember-cli-build.js to broccoli-concat as sourceMapConfig! So no other libs would need updating! Nice forward thinking

[apellerano-pw]

This is merged now from #64. For posterity, if you make it here wanting inline sourcemaps in your Ember build, you can do this in your ember-cli-build.js

sourcemaps: {
  enabled: true,
  mapStyle: 'data',
},

If you want this for your CSS as well, here is the config for dart-sass (not sure what the config looks like for node-sass, or other CSS preprocessors)

sassOptions: {
  implementation: require('sass'),
  sourceMap: true,
  sourceMapEmbed: true,
},