Add `Site#in_cache_dir` helper method (#7160)

Merge pull request 7160

lib/jekyll/site.rb

@@ -2,7 +2,7 @@
 
 module Jekyll
   class Site
-    attr_reader   :source, :dest, :config
+    attr_reader   :source, :dest, :cache_dir, :config
     attr_accessor :layouts, :pages, :static_files, :drafts,
                   :exclude, :include, :lsi, :highlighter, :permalink_style,
                   :time, :future, :unpublished, :safe, :plugins, :limit_posts,
@@ -22,6 +22,8 @@ module Jekyll
 
       self.config = config
 
+      @cache_dir       = in_source_dir(config["cache_dir"])
+
       @reader          = Reader.new(self)
       @regenerator     = Regenerator.new(self)
       @liquid_renderer = LiquidRenderer.new(self)
@@ -401,6 +403,18 @@ module Jekyll
       end
     end
 
+    # Public: Prefix a given path with the cache directory.
+    #
+    # paths - (optional) path elements to a file or directory within the
+    #         cache directory
+    #
+    # Returns a path which is prefixed with the cache directory.
+    def in_cache_dir(*paths)
+      paths.reduce(cache_dir) do |base, path|
+        Jekyll.sanitized_path(base, path)
+      end
+    end
+
     # Public: The full path to the directory that houses all the collections registered
     # with the current site.
     #

test/test_site.rb

@@ -85,6 +85,11 @@ class TestSite < JekyllUnitTest
       assert File.directory?(source_dir(".jekyll-cache", "Jekyll", "Cache"))
       assert File.directory?(source_dir(".jekyll-cache", "Jekyll", "Cache", "Jekyll--Cache"))
     end
+
+    should "use .jekyll-cache directory at source as cache_dir by default" do
+      site = Site.new(default_configuration)
+      assert_equal File.join(site.source, ".jekyll-cache"), site.cache_dir
+    end
   end
 
   context "creating sites" do
@@ -678,5 +683,23 @@ class TestSite < JekyllUnitTest
         refute_equal mtime1, mtime2 # must be regenerated
       end
     end
+
+    context "#in_cache_dir method" do
+      setup do
+        @site = Site.new(
+          site_configuration(
+            "cache_dir" => "../../custom-cache-dir"
+          )
+        )
+      end
+
+      should "create sanitized paths within the cache directory" do
+        assert_equal File.join(@site.source, "custom-cache-dir"), @site.cache_dir
+        assert_equal(
+          File.join(@site.source, "custom-cache-dir", "foo.md.metadata"),
+          @site.in_cache_dir("../../foo.md.metadata")
+        )
+      end
+    end
   end
 end