License comment is breaking the SourceMap

[mattrobenolt]

At the moment, the @sourceMappingURL comment is getting injected into the top of the file after the sourcemap has been generated, resulting in everything being skewed by a few lines.

I've built a tool to help detect these issues: ​http://sourcemap-validator.herokuapp.com/validate?url=http%3A%2F%2Fcode.jquery.com%2Fjquery-1.9.1.min.js

[dmethvin]

Thanks for catching this! An easy solution would be to put a placeholder in the file I suppose.

[mattrobenolt]

What's the reason for it being injected at the top? It seems to be just to save a couple bytes, since there's already a block comment? As opposed to having one at the top and one at the bottom?

[dmethvin]

See #13274 for info. If someone uses //@sourceMappingURL=... in their file it won't work in IE if conditional JS is turned on. Your tool will want to check for that.

I'd actually prefer to see a different comment sequence entirely since you can see what it requires for us to fix.

[mattrobenolt]

Yeah, I followed along with that. Unfortunately, //@ sourceMappingURL= is hardcoded into browsers currently, so something will have to change upstream to change that sequence of characters. If we want to petition for that, I'm open.

The spec is here: ​https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit Mailing list: ​https://lists.mozilla.org/listinfo/dev-js-sourcemap

FWIW, the spec also specifically says at the bottom of the document, but according to both FF and Webkit source, neither care. It can be anywhere in the document.

In my Python implementation, I explicitly check both because of jQuery. :) ​https://github.com/mattrobenolt/python-sourcemap/blob/master/sourcemap/__init__.py#L28-L35

[m_gol]

Enclosing the

//@ sourceMappingURL=jquery.min.map

comment withing /* */ comment block solves the IE conditional JS compilation, doesn't it? It could be at the bottom of the file then, although it would add a few bytes, obviously.

dmethvin, where would you put this placeholder? Won't uglifyjs source map generator account for it, thus making the workaround futile?

TBH, I'd prefer browser vendors (and the spec) to accept /*@ sourceMappingURL=...*/, too. Will that fix the IE conditional compilation problem? If so, it's worth to report it on crbug.com, Chrome guys respond quite quickly to DevTools related issues.

Or maybe just the @ symbol should be changed to sth non-conflicting with IE.

[mattrobenolt]

Backbone does what you're suggesting: ​http://documentcloud.github.io/backbone/backbone-min.js They just do the whole:

/*
//@ sourceMappingURL=backbone-min.map
*/

It feels really lame though. :( This should get pushed up to browsers before this becomes too mainstream and harder to change, in my opinion.

[m_gol]

I agree spec is not ideal here. Using IE conditional JS switches is a bad idea but unfortunately it happens.

I raised the issue here: ​https://groups.google.com/forum/?fromgroups=#!topic/mozilla.dev.js-sourcemap/4uo7Z5nTfUY

[gibson042]

grunt-contrib-uglify appears to ignore banner when generating maps, making them invalid for the resulting minified files. I'll try working around it on our end, but will also file a ticket there.

[Richard Gibson]

Fix #13776: Add banner before generating source map. Close gh-1246.

Changeset: 9d16fe6283667396094d49559a37fc672c06252c

[gibson042]

Upstream issue: ​https://github.com/gruntjs/grunt-contrib-uglify/issues/22

[m_gol]

This has actually been fully fixed with this bug: ​http://bugs.jquery.com/ticket/13793