Fix relative urls & source maps

fixes #284

lib/sprockets/asset.rb

@@ -67,6 +67,13 @@ def digest_path
       logical_path.sub(/\.(\w+)$/) { |ext| "-#{etag}#{ext}" }
     end
 
+    # Public: Return load path + logical path with digest spliced in.
+    #
+    # Returns String.
+    def full_digest_path
+      File.join(@load_path, digest_path)
+    end
+
     # Public: Returns String MIME type of asset. Returns nil if type is unknown.
     attr_reader :content_type
 

lib/sprockets/path_utils.rb

@@ -6,6 +6,7 @@ module Sprockets
   # when code actually wants to reference ::FileUtils.
   module PathUtils
     extend self
+    require 'pathname'
 
     # Public: Like `File.stat`.
     #
@@ -73,8 +74,6 @@ def entries(path)
     #
     # Returns true if path is absolute, otherwise false.
     if File::ALT_SEPARATOR
-      require 'pathname'
-
       # On Windows, ALT_SEPARATOR is \
       # Delegate to Pathname since the logic gets complex.
       def absolute_path?(path)
@@ -102,6 +101,18 @@ def relative_path?(path)
       path =~ /^\.\.?($|#{SEPARATOR_PATTERN})/ ? true : false
     end
 
+    # Public: Get relative path from `start` to `dest`.
+    #
+    # start - String start path (file or dir)
+    # dest  - String destination path
+    #
+    # Returns relative String path from `start` to `dest`
+    def relative_path_from(start, dest)
+      start, dest = Pathname.new(start), Pathname.new(dest)
+      start = start.dirname unless start.directory?
+      dest.relative_path_from(start).to_s
+    end
+
     # Internal: Get relative path for root path and subpath.
     #
     # path    - String path

lib/sprockets/source_map_comment_processor.rb

@@ -21,8 +21,10 @@ def self.call(input)
       uri, _ = env.resolve!(input[:filename], accept: map_type)
       map = env.load(uri)
 
+      path = PathUtils.relative_path_from(input[:filename], map.full_digest_path)
+
       asset.metadata.merge(
-        data: asset.source + (comment % map.digest_path),
+        data: asset.source + (comment % path),
         links: asset.links + [asset.uri, map.uri]
       )
     end

lib/sprockets/source_map_utils.rb

@@ -136,6 +136,9 @@ def encode_json_source_map(mappings, sources: nil, names: nil, filename: nil)
       case mappings
       when String
       when Array
+        mappings.each do |m|
+          m[:source] = relative_path_from(filename, m[:source])
+        end if filename
         sources ||= mappings.map { |m| m[:source] }.uniq.compact
         names   ||= mappings.map { |m| m[:name] }.uniq.compact
         mappings = encode_vlq_mappings(mappings, sources: sources, names: names)