Allow the user to set collections_dir to put all collections under one subdirectory (#6331)

Merge pull request 6331

docs/_docs/collections.md

@@ -46,6 +46,17 @@ defaults:
       layout: page
 ```
 
+**New**: You can optionally specify a directory if you want to store all your collections
+in the same place:
+
+```yaml
+collections:
+  collections_dir: my_collections
+```
+
+Then Jekyll will look in `my_collections/_books` for the `books` collection, and
+in `my_collections/_recipes` for the `recipes` collection.
+
 ### Step 2: Add your content {#step2}
 
 Create a corresponding folder (e.g. `<source>/_my_collection`) and add

docs/_docs/configuration.md

@@ -602,12 +602,13 @@ file or on the command-line.
 
 ```yaml
 # Where things are
-source:       .
+source:          .
-destination:  ./_site
+destination:     ./_site
-plugins_dir:  _plugins
+collections_dir: .
-layouts_dir:  _layouts
+plugins_dir:     _plugins
-data_dir:     _data
+layouts_dir:     _layouts
-includes_dir: _includes
+data_dir:        _data
+includes_dir:    _includes
 collections:
   posts:
     output:   true

lib/jekyll/collection.rb

@@ -100,7 +100,9 @@ module Jekyll
     # Returns a String containing the directory name where the collection
     #   is stored on the filesystem.
     def relative_directory
-      @relative_directory ||= "_#{label}"
+      @relative_directory ||= Pathname.new(directory).relative_path_from(
+        Pathname.new(site.source)
+      ).to_s
     end
 
     # The full path to the directory containing the collection.
@@ -108,7 +110,9 @@ module Jekyll
     # Returns a String containing th directory name where the collection
     #   is stored on the filesystem.
     def directory
-      @directory ||= site.in_source_dir(relative_directory)
+      @directory ||= site.in_source_dir(
+        File.join(site.config["collections_dir"], "_#{label}")
+      )
     end
 
     # The full path to the directory containing the collection, with

lib/jekyll/configuration.rb

@@ -8,6 +8,7 @@ module Jekyll
       # Where things are
       "source"              => Dir.pwd,
       "destination"         => File.join(Dir.pwd, "_site"),
+      "collections_dir"     => "",
       "plugins_dir"         => "_plugins",
       "layouts_dir"         => "_layouts",
       "data_dir"            => "_data",