Completely skip computation if nothing has changed

This commit introduces a global dirty state. This check is used when
invoking a project. It checks to see if any of the known files have
changed, or if any files have been deleted or added. Projects are dirty
if the assetfile has changed. When projects are clean invoking them does
nothing. This check saves costly build time. The build tree is
constructed internally every time. This can be costly. Running those
rake tasks would not change anything anyway so that process can be by
passed.

This commit should make the preview server much faster. Say you have a
set set of assets: images, application.js, application.css, and
index.html. Opening the preview server will send an HTTP request for
index.html. This request will compile the pipeline. Further requests to
application.js, application.css and images should return almost
instantly because pipeline does not have to do any processing.

lib/rake-pipeline.rb

@@ -333,6 +333,7 @@ def invoke
     def setup
       setup_filters
       generate_rake_tasks
+      record_input_files
     end
 
     # Set up the filters. This will loop through all of the filters for
@@ -447,5 +448,17 @@ def assert_input_provided
       end
     end
 
+    # This is needed to ensure that every file procesed in the pipeline
+    # has an entry in the manifest. This is used to compare input files
+    # for the global dirty check
+    def record_input_files
+      input_files.each do |file|
+        full_path = file.fullpath
+
+        if File.exists?(full_path) && !manifest[full_path]
+          manifest[full_path] ||= ManifestEntry.new({}, File.mtime(full_path).to_i)
+        end
+      end
+    end
   end
 end

lib/rake-pipeline/filter.rb

@@ -207,6 +207,7 @@ def generate_rake_tasks
         @rake_tasks = outputs.map do |output, inputs|
           additional_paths = []
           inputs.each do |input|
+
             create_file_task(input.fullpath).dynamic do
               additional_paths += additional_dependencies(input)
             end

lib/rake-pipeline/manifest.rb

@@ -58,6 +58,25 @@ def [](key)
       def []=(key, value)
         @entries[key] = value
       end
+
+      def empty?
+        entries.empty?
+      end
+
+      def files
+        entries.inject({}) do |hash, pair| 
+          file = pair.first
+          entry = pair.last
+
+          hash.merge!(file => entry.mtime)
+
+          entry.deps.each_pair do |name, time| 
+            hash.merge!(name => time)
+          end
+
+          hash
+        end
+      end
     end
   end
 end

lib/rake-pipeline/project.rb

@@ -110,16 +110,15 @@ def build(&block)
       # @see Rake::Pipeline#invoke
       def invoke
         @invoke_mutex.synchronize do
-          if assetfile_path
-            source = File.read(assetfile_path)
-            if digest(source) != assetfile_digest
-              rebuild_from_assetfile(assetfile_path, source)
-            end
-          end
-
           last_manifest.read_manifest
-          pipelines.each(&:invoke)
-          manifest.write_manifest
+
+          if dirty?
+            rebuild_from_assetfile(assetfile_path) if assetfile_dirty?
+
+            pipelines.each(&:invoke)
+
+            manifest.write_manifest
+          end
         end
       end
 
@@ -264,6 +263,58 @@ def setup_pipelines
       def digest(str)
         Digest::SHA1.hexdigest(str)
       end
+
+      def dirty?
+        assetfile_dirty? || files_dirty?
+      end
+
+      def assetfile_dirty?
+        if assetfile_path
+          source = File.read(assetfile_path)
+          digest(source) != assetfile_digest
+        else
+          false
+        end
+      end
+
+      # Returns true if any of these conditions are met:
+      # The pipeline hasn't been invoked yet
+      # The input files have been modified
+      # Any of the input files have been deleted
+      # There are new input files
+      def files_dirty?
+        return true if manifest.empty?
+
+        previous_files = manifest.files
+
+        input_files.each do |input_file|
+          if !File.exists? input_file
+            return true # existing input file has been deleted
+          elsif !previous_files[input_file]
+            return true # there is a new file in the pipeline
+          elsif File.mtime(input_file).to_i != previous_files[input_file]
+            return true # existing file has been changed
+          end
+        end
+
+        false
+      end
+
+      def input_files
+        static_input_files = pipelines.collect do |p|
+          p.input_files.reject { |file| file.in_directory? tmpdir }.map(&:fullpath)
+        end.flatten
+
+        dynamic_input_files = static_input_files.collect do |file|
+          if manifest[file] 
+            manifest[file].deps.keys
+          else
+            nil
+          end
+        end.flatten.compact
+
+        static_input_files + dynamic_input_files
+      end
     end
   end
 end

spec/rake_acceptance_spec.rb

@@ -163,6 +163,7 @@ def copy_files
 
     it "can be configured using the pipeline" do
       pipeline = Rake::Pipeline.new
+      pipeline.project = Rake::Pipeline::Project.new
       pipeline.add_input tmp, 'app/javascripts/*.js'
       pipeline.output_root = File.expand_path("public")
       pipeline.tmpdir = "temporary"