Class: Sprockets::AddSourceMapCommentToAssetProcessor

Relationships & Source Files
Inherits:	Object
Defined in:	lib/sprockets/add_source_map_comment_to_asset_processor.rb

Overview

This is a processor designed to add a source map “comment” to the bottom of a css or JS file that is serving a source map. An example of a comment might look like this

//# application.js-80af0efcc960fc2ac93eda2f7b12e3db40ab360bf6ea269ceed3bea3678326f9.map

As an asset is built it gets source map information added to the asset.to_hash[:metadata][:map] key. This contains all the information that is needed to build a source map file.

To add this comment we must have an asset we can link to. To do this we ensure that the original asset is loaded, then we use a use a special mime type. For example application/js-sourcemap+json for a JS source map.

This will trigger a new asset to be loaded and generated by the SourceMapProcessor processor.

Finally once we have that file, we can generate a link to it with it’s full fingerprint. This is done and then added to the original asset as a comment at the bottom.

Class Method Summary

.call(input)

Class Method Details

.call(input)

[ GitHub ]

# File 'lib/sprockets/add_source_map_comment_to_asset_processor.rb', line 29


def self.call(input)

  case input[:content_type]
  when "application/javascript"
    comment = "\n//# sourceMappingURL=%s"
    map_type = "application/js-sourcemap+json"
  when "text/css"
    comment = "\n/*# sourceMappingURL=%s */"
    map_type = "application/css-sourcemap+json"
  else
    fail input[:content_type]
  end

  env = input[:environment]

  uri, _ = env.resolve!(input[:filename], accept: input[:content_type])
  asset = env.load(uri)

  uri, _ = env.resolve!(input[:filename], accept: map_type)
  map = env.load(uri)

  uri, params = URIUtils.parse_asset_uri(input[:uri])
  uri = env.expand_from_root(params[:index_alias]) if params[:index_alias]
  path = PathUtils.relative_path_from(PathUtils.split_subpath(input[:load_path], uri), map.digest_path)

  asset.metadata.merge(
    data: asset.source + (comment % path) + "\n",
    links: asset.links + [asset.uri, map.uri]
  )
end