Add force-sourcemap to embed inline sourcemaps

[zakhenry]

This allows a flag to be added to force the embedding of an inline sourcemap to the file. This resolves issues with webpack not outputting sourcemaps for tools like remap-istanbul to function.

I have published this separately at https://www.npmjs.com/package/sourcemap-istanbul-instrumenter-loader if you want to test

[TheLarkInn]

@zakhenry do you perhaps have an example repo that contains typescript with webpack and coverage like this? Is remap-instanbul also required?

[zakhenry]

@TheLarkInn yea this is used in https://github.com/ubiquits/toolchain/blob/master/cli/tasks/test.js and yes remap istanbul is required. Note that the setup isn't trivial though as I merge two coverage reports from two sources (frontend and backend unit tests)

[bryanforbes]

Is there a reason this needs to be hidden behind a flag? Can't this simply be:

if (sourceMap) {
    var encoded = new Buffer(JSON.stringify(sourceMap)).toString('base64');
    source += '\n\n//# sourceMappingURL=data:application/json;base64,' + encoded;
}

If someone wants to ignore source maps, they can use exclude.

[zakhenry]

This is more of a hack as there may actually be standalone source maps alongside, but they don't seem to work for reasons I forget. This pr allows forcing an inline sourcemap to be appended, I don't think its actually a good long-term solution

[bryanforbes]

When you say, "standalone source maps alongside," do you mean source maps that aren't inlined but are in, for instance, a .js.map file?

[zakhenry]

Yea that's the one, though with webpack I'm a bit fuzzy with what point the source maps are output

[zakhenry]

It's been a while since I did this PR so the details have escaped me

[bryanforbes]

From my understanding, the second parameter (sourceMap) will be null or undefined unless a previous loader in the chain has provided one. Most transpiling loaders provide the sourceMap parameter, but for third-party code (ex. Angular 2, bootstrap, etc.) you have to use source-map-loader. source-map-loader will load both inline and external source maps, which should solve the problem you were seeing. Even so, if the second parameter of the loader isn't provided, a sourceMappingURL shouldn't be generated for the code since it will only cause webpack to process an object that it shouldn't even have to look at.

[bryanforbes]

@deepsweet Is there any way we can get you to take a look at this pull request? I don't think the logic needs to be behind a flag/property, but this issue is preventing instrumented transpiled code from being able to be remapped back to the original code via remap-istanbul.

[samvloeberghs]

@bryanforbes, @deepsweet seems to be active on github as he has activity, probably notifications turned off or something. Anyway I tweeted him as I need this as well! https://twitter.com/samvloeberghs/status/773126385074311168

[deepsweet]

hey guys. I'll merge #28 later today.