Take into account when a sprite image changes and is recompiled

lib/spritely/sass_functions.rb

@@ -4,7 +4,7 @@ module Spritely
   module SassFunctions
     def spritely_map(glob, kwargs = {})
       SpriteMap.create(glob.value, kwargs).tap do |sprite_map|
-        reset_sprockets_directory_cache!
+        reset_sprockets_caches!(sprite_map)
         sprockets_context.depend_on(Spritely.directory)
         sprite_map.files.each do |file|
           sprockets_context.depend_on(file)
@@ -60,8 +60,12 @@ def find_image(sprite_map, image_name)
       sprite_map.find(image_name.value) || raise(Sass::SyntaxError, "No image '#{image_name.value}' found in sprite map '#{sprite_map.name}'.")
     end
 
-    def reset_sprockets_directory_cache!
-      sprockets_context.environment.send(:trail).instance_variable_get(:@entries).delete(Spritely.directory.to_s)
+    def reset_sprockets_caches!(sprite_map)
+      sprockets_environment.instance_variable_get(:@assets).delete_if { |_, asset| asset.pathname == sprite_map.filename }
+      sprockets_environment.send(:trail).tap do |trail|
+        trail.instance_variable_get(:@entries).delete(Spritely.directory.to_s)
+        trail.instance_variable_get(:@stats).delete(sprite_map.filename.to_s)
+      end
     end
   end
 end

spec/fixtures/rails-app-changes/app/assets/stylesheets/sprites.css.scss

@@ -0,0 +1,26 @@
+$application-sprite: spritely-map("application/*.png",
+  $background-repeat: true,
+  $football-spacing: 100px,
+  $mario-spacing: 10px,
+  $mario-position: right,
+  $spacing: 5px
+);
+
+body {
+  background-image: spritely-url($application-sprite);
+  background-position: spritely-position($application-sprite, "background");
+}
+
+#mario {
+  background-image: spritely-url($application-sprite);
+  background-position: spritely-position($application-sprite, "mario");
+  width: spritely-width($application-sprite, "mario");
+  height: spritely-height($application-sprite, "mario");
+}
+
+#arrow {
+  background-image: spritely-url($application-sprite);
+  background-position: spritely-position($application-sprite, "dropdown-arrow");
+  width: spritely-width($application-sprite, "dropdown-arrow");
+  height: spritely-height($application-sprite, "dropdown-arrow");
+}

spec/integration/precompilation_spec.rb

@@ -34,4 +34,12 @@
     expect(File).to exist(File.join('app', 'assets', 'images', 'sprites', 'application.png'))
     expect(File).to exist(File.join('app', 'assets', 'images', 'sprites', 'foo.png'))
   end
+
+  it 'should correctly compile a new sprite image and CSS when files change' do
+    compile_assets
+    FileUtils.cp_r "#{__dir__}/../fixtures/rails-app-changes/.", "."
+    compile_assets
+    sprite_files = Dir.glob(File.join('public', 'assets', 'sprites', 'application-*.png'))
+    expect(sprite_files.length).to eq(2)
+  end
 end

spec/spritely/sass_functions_spec.rb

@@ -1,9 +1,11 @@
 require 'spec_helper'
 require 'sprockets'
+require 'ostruct'
 
 describe Spritely::SassFunctions do
   class SpriteMapDouble < Sass::Script::Literal
     def name; 'test'; end
+    def filename; 'test.png'; end
     def files; []; end
   end
 
@@ -25,17 +27,19 @@ def files; []; end
     end
   end
 
-  shared_examples "a sprite function that resets the sprockets directory cache" do
-    it 'should clear out the trail entries' do
+  shared_examples "a sprite function that resets the sprockets directory caches" do
+    it 'should clear out the trail caches' do
       subject
+      expect(environment.instance_variable_get(:@assets).length).to eq(0)
       expect(environment.send(:trail).instance_variable_get(:@entries)).to_not have_key(directory)
+      expect(environment.send(:trail).instance_variable_get(:@stats)).to_not have_key('test.png')
     end
   end
 
   describe '#spritely_url' do
     subject { evaluate(".background-image { background-image: spritely-url(spritely-map('test/*.png')); }") }
 
-    it_should_behave_like "a sprite function that resets the sprockets directory cache"
+    it_should_behave_like "a sprite function that resets the sprockets directory caches"
 
     it { should eq(".background-image {\n  background-image: url(sprites/test.png); }\n") }
   end
@@ -44,7 +48,7 @@ def files; []; end
     subject { evaluate(".background-position { background-position: spritely-position(spritely-map('test/*.png'), 'bar'); }") }
 
     it_should_behave_like "a sprite function that checks image existence"
-    it_should_behave_like "a sprite function that resets the sprockets directory cache"
+    it_should_behave_like "a sprite function that resets the sprockets directory caches"
 
     it { should eq(".background-position {\n  background-position: -10px -12px; }\n") }
 
@@ -59,7 +63,7 @@ def files; []; end
     subject { evaluate(".background { background: spritely-background(spritely-map('test/*.png'), 'bar'); }") }
 
     it_should_behave_like "a sprite function that checks image existence"
-    it_should_behave_like "a sprite function that resets the sprockets directory cache"
+    it_should_behave_like "a sprite function that resets the sprockets directory caches"
 
     it { should eq(".background {\n  background: url(sprites/test.png) -10px -12px; }\n") }
   end
@@ -68,7 +72,7 @@ def files; []; end
     subject { evaluate(".width { width: spritely-width(spritely-map('test/*.png'), 'bar'); }") }
 
     it_should_behave_like "a sprite function that checks image existence"
-    it_should_behave_like "a sprite function that resets the sprockets directory cache"
+    it_should_behave_like "a sprite function that resets the sprockets directory caches"
 
     it { should eq(".width {\n  width: 25px; }\n") }
   end
@@ -77,7 +81,7 @@ def files; []; end
     subject { evaluate(".height { height: spritely-height(spritely-map('test/*.png'), 'bar'); }") }
 
     it_should_behave_like "a sprite function that checks image existence"
-    it_should_behave_like "a sprite function that resets the sprockets directory cache"
+    it_should_behave_like "a sprite function that resets the sprockets directory caches"
 
     it { should eq(".height {\n  height: 50px; }\n") }
   end
@@ -88,7 +92,9 @@ def evaluate(value)
 
   def environment
     @environment ||= Sprockets::Environment.new.tap do |environment|
+      environment.instance_variable_set(:@assets, {'test' => OpenStruct.new(pathname: 'test.png')})
       environment.send(:trail).instance_variable_set(:@entries, {'spritely-directory' => 'blah'})
+      environment.send(:trail).instance_variable_set(:@stats, {'test.png' => 'blah'})
       environment.context_class.class_eval do
         def asset_path(path, options = {})
           path