Feature: CoffeeScript Source Map Support

[vjpr]

http://ryanflorence.com/2012/coffeescript-source-maps/

Only a few simple changes needed:

1. Add a new PostProcessor for application/javascript

# stdlib
path = require "path"

# internal
Template = require "mincer/lib/mincer/template"

#//////////////////////////////////////////////////////////////////////////////

# Class constructor
SourceMapComments = module.exports = SourceMapComments = ->
  Template.apply this, arguments

require("util").inherits SourceMapComments, Template

# Process data
SourceMapComments::evaluate = (context, locals, callback) ->
  pathname = path.join(context.rootPath, context.logicalPath)
  @data = "\n\n//@ sourceMappingURL=#{pathname}.map\n\n" + @data
  callback null, @data

@env.registerPostProcessor 'application/javascript', require('./SourceMapComments')

1. Serve .map files compiled with CoffeeScriptRedux. I'm digging into this now to see how it integrates with Mincer.

---

Generating source maps involves the following code:

csAst = coffee.parse input
jsAst = coffee.compile csAst
sourceMap = coffee.sourceMap jsAst

Should be as easy as using an engine to handle the .map extension.

[vjpr]

Not as straightforward as I first thought.

Below is a very rough, proof-of-concept. Manages to show CoffeeScript source in browser - but is unusably slow, incorrect line number mapping due to PostProcessors, and very badly integrated.

CoffeeScriptRedux has a ton of bugs too.

# mincer/server.js:310

  var path = require('path')

  // If asset is a `.coffee` file we return the coffee file.
  if (path.extname(pathname) === '.coffee') {

    //var pathname = pathname.slice(0, -7)
    var asset = this.environment.findAsset(pathname)
    var source = require('fs').readFileSync(asset.pathname, 'utf8')
    return res.end(new Buffer(source))

  // If asset is a `.map` file we compile the source map.
  } else if (path.extname(pathname) === '.map') {

    var pathname = pathname.slice(0, -4)
    var asset = this.environment.findAsset(pathname)
    console.log (asset.pathname)
    if (path.extname(asset.pathname) === '.coffee') {
      var input = require('fs').readFileSync(asset.pathname, 'utf8')
      var coffee = require("/Users/Vaughan/dev/CoffeeScriptRedux")
      var csAst = coffee.parse(input)
      var jsAst = coffee.compile(csAst)
      var sourceMap = coffee.sourceMap(jsAst, path.basename(asset.logicalPath) + '.coffee')
      return res.end(new Buffer(sourceMap))
    }

  }

[vjpr]

Just found the branch being worked on for Sprockets: sstephenson/sprockets#311. Seems to be aimed at source maps for the concatenated Javascript use case, not the Javascript to CoffeeScript use case.

Using the X-SourceMap header instead of comments is probably a better approach most of the time.

Also, using a query string like ?source=true looks like a good approach to get .coffee files.

[puzrin]

Anyway, we should wait until UglifyJS v2 released https://github.com/mishoo/UglifyJS2

[rubemz]

I believe it is already released https://github.com/mishoo/UglifyJS2/tags

[jpillora]

+1

[puzrin]

This ticket is closed as not enougth generic, in flavour of #116 .