Adding directive depends_on_directory

`depends_on_directory` allows you to specify all files (non-recurisve)
in a directory to watch for changes. This is helpful in cases where
files may be dynamic or there are many files.

CHANGELOG.md

@@ -5,6 +5,7 @@ Get upgrade notes from Sprockets 3.x to 4.x at https://github.com/rails/sprocket
 ## Master
 
 - Fix for Ruby 2.7 keyword arguments warning in `base.rb`. [#660](https://github.com/rails/sprockets/pull/660)
+- Adding new directive `depend_on_directory` [#668](https://github.com/rails/sprockets/pull/668)
 
 ## 4.0.0
 

README.md

@@ -119,6 +119,7 @@ Here is a list of the available directives:
 - [`link_directory`](#link_directory) - Make target directory compile and be publicly available without adding contents to current
 - [`link_tree`](#link_tree) - Make target tree compile and be publicly available without adding contents to current
 - [`depend_on`](#depend_on) - Recompile current file if target has changed
+- [`depend_on_directory`](#depend_on_directory) - Recompile current file if any files in target directory has changed
 - [`stub`](#stub) - Ignore target file
 
 You can see what each of these does below.
@@ -239,7 +240,7 @@ The first time this file is compiled the `application.js` output will be written
 
 So, if `b.js` changes it will get recompiled. However instead of having to recompile the other files from `a.js` to `z.js` since they did not change, we can use the prior intermediary files stored in the cached values . If these files were expensive to generate, then this "partial" asset cache strategy can save a lot of time.
 
-Directives such as `require`, `link`, and `depend_on` tell Sprockets what assets need to be re-compiled when a file changes. Files are considered "fresh" based on their mtime on disk and a combination of cache keys.
+Directives such as `require`, `link`, `depend_on`, and `depend_on_directory` tell Sprockets what assets need to be re-compiled when a file changes. Files are considered "fresh" based on their mtime on disk and a combination of cache keys.
 
 On Rails you can force a "clean" install by clearing the `public/assets` and `tmp/cache/assets` directories.
 
@@ -445,11 +446,50 @@ you need to tell sprockets that it needs to re-compile the file if `bar.data` ch
 var bar = '<%= File.read("bar.data") %>'
 ```
 
+To depend on an entire directory containing multiple files, use `depend_on_directory`
+
 ### depend_on_asset
 
 `depend_on_asset` *path* works like `depend_on`, but operates
 recursively reading the file and following the directives found. This is automatically implied if you use `link`, so consider if it just makes sense using `link` instead of `depend_on_asset`.
 
+### depend_on_directory
+
+`depend_on_directory` *path* declares all files in the given *path* without
+including them in the bundle. This is useful when you need to expire an
+asset's cache in response to a change in multiple files in a single directory.
+
+All paths are relative to your declaration and must begin with `./`
+
+Also, your must include these directories in your [load path](guides/building_an_asset_processing_framework.md#the-load-path).
+
+**Example:**
+
+If we've got a directory called `data` with files `a.data` and `b.data`
+
+```a.data
+A
+```
+
+```b.data
+B
+```
+
+```js.erb
+//= depend_on_directory ./data
+var a = '<% File.read('data/a.data') %>'
+var b = '<% File.read('data/b.data') %>'
+```
+
+Would produce:
+
+```js
+var a = "A";
+var b = "B";
+```
+
+You can also see [Index files are proxies for folders](#index-files-are-proxies-for-folders) for another method of organizing folders that will give you more control.
+
 ### stub
 
 `stub` *path* excludes that asset and its dependencies from the asset bundle.
@@ -491,9 +531,9 @@ When you modify the `logo.png` on disk, it will force `application.css` to be
 recompiled so that the fingerprint will be correct in the generated asset.
 
 You can manually make sprockets depend on any other file that is generated
-by sprockets by using the `depend_on` directive. Rails implements the above
-feature by auto calling `depend_on` on the original asset when the `asset_url`
-is used inside of an asset.
+by sprockets by using the `depend_on` or `depend_on_directory` directive. Rails
+implements the above feature by auto calling `depend_on` on the original asset
+when the `asset_url` is used inside of an asset.
 
 ### Styling with Sass and SCSS
 

lib/sprockets/directive_processor.rb

@@ -285,6 +285,24 @@ def process_depend_on_asset_directive(path)
         to_load(resolve(path))
       end
 
+      # Allows you to state a dependency on a relative directory
+      # without including it.
+      #
+      # This is used for caching purposes. Any changes made to
+      # the dependency directory will invalidate the cache of the
+      # source file.
+      #
+      # This is useful if you are using ERB and File.read to pull
+      # in contents from multiple files in a directory.
+      #
+      #     //= depend_on_directory ./data
+      #
+      def process_depend_on_directory_directive(path = ".", accept = nil)
+        path = expand_relative_dirname(:depend_on_directory, path)
+        accept = expand_accept_shorthand(accept)
+        resolve_paths(*@environment.stat_directory_with_dependencies(path), accept: accept)
+      end
+
       # Allows dependency to be excluded from the asset bundle.
       #
       # The `path` must be a valid asset and may or may not already
@@ -374,7 +392,7 @@ def resolve_paths(paths, deps, **kargs)
           next if subpath == @filename || stat.directory?
           uri, deps = @environment.resolve(subpath, **kargs)
           @dependencies.merge(deps)
-          yield uri if uri
+          yield uri if uri && block_given?
         end
       end
 

test/test_asset.rb

@@ -123,6 +123,50 @@ def self.test(name, &block)
       end
     end
   end
+
+  test "modify asset's dependency file in directory" do
+    main = fixture_path('asset/test-main.js.erb')
+    dep  = fixture_path('asset/data/foo.txt')
+    begin
+      ::FileUtils.mkdir File.dirname(dep)
+      sandbox main, dep do
+        write(main, "//= depend_on_directory ./data\n<%= File.read('#{dep}') %>")
+        write(dep, "a;")
+        asset      = asset('test-main.js')
+        old_digest = asset.hexdigest
+        old_uri    = asset.uri
+        assert_equal "a;\n", asset.to_s
+
+        write(dep, "b;")
+        asset = asset('test-main.js')
+        refute_equal old_digest, asset.hexdigest
+        refute_equal old_uri, asset.uri
+        assert_equal "b;\n", asset.to_s
+      end
+    ensure
+      ::FileUtils.rmtree File.dirname(dep)
+    end
+  end
+
+  test "asset's dependency on directory exists" do
+    main = fixture_path('asset/test-missing-directory.js.erb')
+    dep  = fixture_path('asset/data/foo.txt')
+
+    begin
+      sandbox main, dep do
+        ::FileUtils.rmtree File.dirname(dep)
+        write(main, "//= depend_on_directory ./data")
+        assert_raises(Sprockets::ArgumentError) do
+          asset('test-missing-directory.js')
+        end
+
+        ::FileUtils.mkdir File.dirname(dep)
+        assert asset('test-missing-directory.js')
+      end
+    ensure
+      ::FileUtils.rmtree File.dirname(dep)
+    end
+  end
 end
 
 class TextStaticAssetTest < Sprockets::TestCase