Error in array-set when producing source maps.

[thlorenz]

I created a repo to reproduce the issue here, but here is the stack trace, it basically breaks in ./lib/array-set.js.

/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/node_modules/source-map/lib/source-map/array-set.js:83
    throw new Error('No element indexed by ' + aIdx);
          ^
Error: No element indexed by 1
    at ArraySet_at [as at] (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/node_modules/source-map/lib/source-map/array-set.js:83:11)
    at SourceMapConsumer_parseMappings [as _parseMappings] (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/node_modules/source-map/lib/source-map/source-map-consumer.js:158:44)
    at new SourceMapConsumer (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/node_modules/source-map/lib/source-map/source-map-consumer.js:100:10)
    at module.exports (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/lib/mappings-from-map.js:10:18)
    at Combiner._addExistingMap (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/index.js:28:18)
    at Combiner.addFile (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/node_modules/combine-source-map/index.js:58:12)
    at Stream.write (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/browser-pack/index.js:42:23)
    at Stream.stream.write (/Users/thlorenz/dev/js/projects/es6ify/tmp/node_modules/browserify/node_modules/through/index.js:26:11)
    at Stream.ondata (stream.js:51:26)
    at Stream.EventEmitter.emit (events.js:95:17)

[fitzgen]

The source map we are trying to parse only has one source listed, but there is a mapping that refers to a second source (at index 1, presumably supposed to be bar.js). This is a bad source map. Looking into which library generates the bad source map (using this lib perhaps?).

{ version: 3,
  file: '/Users/fitzgen/src/repro-sourcemap-issue/foo.js.es6',
  sources: [ '/Users/fitzgen/src/repro-sourcemap-issue/foo.js' ],
  names: [],
  mappings: 'uBAAA,SAAA,CAAS,MAAA,CAAQ;AACL,KAAA,YAAA,EAAc,EAAA,CAAA,CAAI,KAAA,CAAM,MAAA,EAAQ,OAAA,CAAA,mBAA0B,CAAC,MAAA,CAAA;AAC/D,KAAA,EAAS,GAAA,EAAA,EAAI,EAAA,CAAG,EAAA,EAAI,MAAA,CAAA,MAAA,CAAc,EAAA,EAAA,CAAK;AACjC,OAAA,KAAA,EAAO,MAAA,CAAM,CAAA,CAAA;AACjB,eAAA,CAAY,IAAA,CAAA,EAAQ,OAAA,CAAA,wBAA+B,CAAC,MAAA,CAAQ,KAAA,CAAA;AAAA;AAE9D,QAAO,YAAA;AAAA,CAAA,2BCNf,SAAA,CAAS,MAAA,CAAQ,aAAA,CAAc;AACrB,KAAA,KAAA,EAAO,OAAA,CAAA,WAAA;AACX,QAAA,CAAA,cAAqB,CAAC,MAAA,CAAQ,cAAA,CAAe,EAAC,UAAA,CAAY,MAAA,CAAA,CAAA;AAC1D,MAAA,CAAA,SAAA,EAAiB,OAAA;AACjB,QAAA,CAAA,gBAAuB,CAAC,IAAA,CAAM,kBAAiB,CAAC,YAAA,CAAA,CAAA;AAChD,QAAO,KAAA;AAAA,CAAA;GCLP,MAAA,ECAN,SAAA,CAAS;AACH,cAAA;AACI,cAAoB,0BAAmB;AAFjD,eAAA,CAAa,SAAA,CAAS,CAAE,EAAA,CAAA;UDCpB,SAAA,CAAM,CAAE;AACJ,YAAO,KAAA;AAAA;AAAA,GAAA;ACET;CACD,CAAA,CAAA;ADAL,MAAA,CAAA,OAAA,EAAiB,MAAA',
  sourcesContent: [ 'class Hello {\n    greet() {\n        return "me";\n    }\n}\nmodule.exports = Hello;\n' ] }

[thlorenz]

Oh so maybe the combined-source-map module is using source-map generator incorrectly. This may be related to the latest change to that module.

@ben-ng do you have an idea what could be going wrong here?

[fitzgen]

Aside: the combine-source-map module can get a lot smaller and dumber once we make progress with issue(s) 16/69

[thlorenz]

@fitzgen Yeah those pieces in the works look interesting. combine-source-map will most likely just have to be a rather simple wrapper at that point.

I rolled back the change that caused the problem for now and am waiting for feedback from the author of that PR to see how to proceed. How long do you think until those mentioned changes land? Possibly we should wait with the combine-source-map migration to use this module until then?

[fitzgen]

@thlorenz It is fairly low priority on my TODO list; I'm spending 99% of my hack time on new features for firefox's debugger. If you want to take a crack at it, I will provide speedy review of pull requests :) We did end up deciding on an API in issue 16.

I am flying back to SF from Paris on Saturday, maybe I can take a crack at it then.

[thlorenz]

Somewhat swamped myself here, but for me personally this is not such high priority either. As far as I understand the original change was attempted to fix problems with source-maps of minified code that @ben-ng ran into.
If this is more important for his module I'll leave this up to him ;)

[ben-ng]

I've been on a road trip through the midwest, finally got back on the internet today.

Yes, this change is very important for my module so i'll fix this one. Thanks for helping with the repro case @thlorenz.

[thlorenz]

@ben-ng nice!

[ben-ng]

Okay, this issue is definitely in es6ify. I'll take care of it and send a PR now. Thank you for the repro case!