See if we can utilize WebAssembly source-map stuff

[stefanpenner]

mozilla/source-map#306

cross post: broccolijs/broccoli-concat#120

[Turbo87]

the new stuff is Node 8+, which we can't support until some time next year unfortunately... (see https://github.com/mozilla/source-map/blob/master/package.json#L58)

[vlascik]

You could always bump a major version and have users opt-in to it if they don't need Node 6 (which is probably almost everyone). Source-map generation is ~30% of rebuild time, it makes a lot of sense to try to fix it sooner than next year.

[Turbo87]

we can do that for this lib, yes. but it is used inside Ember CLI and we can't just bump major there and drop Node 6 support earlier than planned.

[vlascik]

I know you can't do it by default, but developers are generally advanced enough users to be able to force a new version for ember-cli via resolutions, if it meant faster rebuilds.

[ef4]

The cost of having two implementations in node is basically not important (especially when you consider that most people end up with possibly dozens of copies of common utility libraries in a big node project). So it's plausible to ship a version of this lib that uses webassembly where available and uses a pure JS implementation otherwise.

[ef4]

(I mean in terms of app performance, obviously there is maintainer overhead. But if we were only keeping the existing JS implementation around for backward compat and kept all new work in the webassembly one, I think it would be manageable.)

[puzrin]

Sorry for stupid question, but why don't you use indexed format for sourcemap concat? It has zero cost and 100% compatibility.

If you care about performance, it would be optimal to load such "concatenated" sourcemap once via sourcemap v0.8.0. It already has all required optimizaions.

[ef4]

Way back when this was written, the indexed format definitely did not have broad compatibility. If that has changed, great.

[puzrin]

Way back when this was written, the indexed format definitely did not have broad compatibility. If that has changed, great.

FYI, some technical details:

1. Chrome supports indexed format, if not multi-level nested. In dev mode (without minifier), build of such map is significantly faster.
2. In our code, [terser (sm 0.6.1 inside) + 1-level indexed sourcemap] vs [terser + fast_concatenated sourcemap] take ~ the same time.