Add sourcemaps on ClosureCompilerFilter

[ciotto]

In order to use opbeat-plain-JS to track JavaScript errors, I added a few features for sourcemaps files creation using the ClosureCompilerFilter.

I also add some test for this part.

[karyon]

please help me understand this. this PR

1. Adds OFFLINE_GROUP_FILES that enables/disables concatenation of files in offline mode (this is what you mean by grouping, right?)
   • It does not add this feature for "online" compression, right?
   • what is the use case for this setting? is not concatenating files a requirement for source maps?
2. Adds CLOSURE_COMPILER_SOURCEMAPS which makes the closure compiler generate source maps
3. Adds OFFLINE_SOURCEMAPS_ON_FILES
   • this i don't quite get. do source maps work without making this true? what's the benefit of encoding this in base64 instead of a normal .map file?

[ciotto]

Hello,
I try to explain:

1. I probably used the wrong name for variable, I did a check and if OFFLINE_GROUP_FILES is False, the concatenation of files is disabled also in "on-line" mode. The correct name can be ENABLE_FILES_CONCATENATION. I added this function becouse, for the flow of compressor, I can't minify more files in one Closur Compiler call, so I can't generate a single .map file for more files.

2. Correct

3. This appear to work also in "on-line" mode, so i used the wrong name. I used the base64 min because the SASS precompiler used this before and because I can't generate the file in the filter, but base64 source map is not largely supported and is not good for download size

Now I use this code in production an it work fine.

I will change the variables names as sun as possible.

[karyon]

ref #438.

closing due to inactivity.

as far as i can see (correct me if i'm wrong), this PR makes the clojure compiler output sourcemaps into files, appends that as a base64 data url to the js file, and then decodes the base64 data, writes it to a file, and replaces the data url with a url pointing to that file. i think this is the wrong approach, a better one would make the compiler put the source map more directly into the storage.

having said that, i would appreciate any new attempt at this, although i'm still not sure how we should handle the different supported compilers, e.g. the default rjsmin doesn't even support sourcemaps.

[ciotto]

I'm sorry for my inactivity, but, even though I use this code in production, I opted for a more usable approach, so I don't spent other time on this develop.

Surely my approach is not the best but, if I remember, CosureCompiler can't write source maps in a separated file. Anyhow, write directly on a storage require a big refactor of the Compressor's logics.

In other words, this is a workaround but work for my purpose.

[karyon]

yeah, "require a big refactor" would also be my first guess. however, django-compressor is quite complex and hard to maintain as it is, and bolting on more workarounds will only worsen this :)