Source maps about ember-app-kit

[rwjblue]

I've been looking at this, and have a few comments/issues:

We are currently chaining together a number of steps for the javascript to reach the final tmp/public/assets/app.js:

• copy:prepare copies from app/**/*.js to tmp/javascript/app/
• transpiler transpiles from tmp/javascript/app/**/*.js to tmp/transpiled/app/
• emberTemplates:compile compiles templates from app/templates/ to tmp/public/assets/templates.js
• concat concats all JS from
• Then additionally for final release we do these tasks:
  • uglify compresses the files identified by useminPrepare
  • rev prepends a hash to the files generated by uglify

In order for our source maps to point back to our original code in app/ we will need each step in the chain to support source maps. (This means that we will have to pass a source map input for everything but the original step.)

Issues with source map support in the current build chain:

• It doesn't look like es6-module-transpiler supports source maps at this point (although I could have missed it). I am looking to see if I can add support using the mozilla/source_map module.
• We need to create a source map during the copy:prepare task (coffeescript can already generate a source map on compile) so that we can pass it in to the transpile task.
• grunt-contrib-concat doesn't support source maps either. There is an alternate that we could use at grunt-concat-sourcemap, but I'm not sure if we want to depend on an external dependency that isn't maintained by the Grunt team...

Another alternative would be to use uglify instead of concat since uglify supports source map in/out and what not. We could tweak the options so that it wouldn't 'mangle' on a standard build (only on build:dist). How do we feel about this in general?

If we either use grunt-concat-sourcemap or uglify to concat, then our only issues are the copy:prepare and es6-module-transpiler.

[kmiyashiro]

Would it be sufficient first step to add source maps to a step at a time? For example, just before the concat/uglify step so that you can at least debug individual modules in dev?

[thomasboyt]

Going to attempt to include source maps for transpiling during the big Esprima refactor i'm doing. most of it is line-to-line so shouldn't be too bad (knock on wood)

After that, main issue for source maps is concat. grunt-concat-sourcemap should be merged into grunt-contrib-concat ASAP, but in the meantime we may just want to use grunt-concat-sourcemap instead. However, it doesn't currently support piping in existing source maps AFAIK, so that'll have to be added.

[thomasboyt]

Added grunt-concat-sourcemap support in 580525d. Result looks like this:

Better than debugging a single concatenated file, at least.

[stefanpenner]

@thomasboyt absolutely, this much better then what we had before. At some point having 1:1 would be great, but this is already a great leap forward.

That being said, I'll leave this issue open until we have the 1:1 solution.

[stefanpenner]

i think leaving the current solution is fine, turns out having debugged a few things. Being able to see the module system preamble, has actually helped me sort or module related issues on many occasions.

I think this can be improved, but for now this seems totally fine.