Add debug output to theme rendering (#5195)

Merge pull request 5195

lib/jekyll/renderer.rb

@@ -169,12 +169,16 @@ def place_in_layouts(content, payload, info)
     # Returns nothing
     private
     def validate_layout(layout)
-      return unless invalid_layout?(layout)
-      Jekyll.logger.warn(
-        "Build Warning:",
-        "Layout '#{document.data["layout"]}' requested "\
-        "in #{document.relative_path} does not exist."
-      )
+      if invalid_layout?(layout)
+        Jekyll.logger.warn(
+          "Build Warning:",
+          "Layout '#{document.data["layout"]}' requested "\
+          "in #{document.relative_path} does not exist."
+        )
+      elsif !layout.nil?
+        layout_source = layout.path.start_with?(site.source) ? :site : :theme
+        Jekyll.logger.debug "Layout source:", layout_source
+      end
     end
 
     # Render layout content into document.output

lib/jekyll/theme.rb

@@ -8,6 +8,8 @@ class Theme
 
     def initialize(name)
       @name = name.downcase.strip
+      Jekyll.logger.debug "Theme:", name
+      Jekyll.logger.debug "Theme source:", root
       configure_sass
     end
 
@@ -21,19 +23,19 @@ def root
     end
 
     def includes_path
-      path_for "_includes".freeze
+      @includes_path ||= path_for "_includes".freeze
     end
 
     def layouts_path
-      path_for "_layouts".freeze
+      @layouts_path ||= path_for "_layouts".freeze
     end
 
     def sass_path
-      path_for "_sass".freeze
+      @sass_path ||= path_for "_sass".freeze
     end
 
     def assets_path
-      path_for "assets".freeze
+      @assets_path ||= path_for "assets".freeze
     end
 
     def configure_sass
@@ -56,6 +58,7 @@ def path_for(folder)
     def realpath_for(folder)
       File.realpath(Jekyll.sanitized_path(root, folder.to_s))
     rescue Errno::ENOENT, Errno::EACCES, Errno::ELOOP
+      Jekyll.logger.warn "Invalid theme folder:", folder
       nil
     end