Merge pull request #4312 from jekyll/fix-layout-metadata

Merge pull request 4312

features/layout_data.feature

@@ -0,0 +1,18 @@
+Feature: Layout data
+  As a hacker who likes to avoid repetition
+  I want to be able to embed data into my layouts
+  In order to make the layouts slightly dynamic
+
+  Scenario: Use custom layout data
+    Given I have a _layouts directory
+    And I have a "_layouts/custom.html" file with content:
+      """
+      ---
+      foo: my custom data
+      ---
+      {{ content }} foo: {{ layout.foo }}
+      """
+    And I have an "index.html" page with layout "custom" that contains "page content"
+    When I run jekyll build
+    Then the "_site/index.html" file should exist
+    And I should see "page content\n foo: my custom data" in "_site/index.html"

lib/jekyll/drops/drop.rb

@@ -62,10 +62,14 @@ module Jekyll
       # and the key matches a method in which case it raises a
       # DropMutationException.
       def []=(key, val)
-        if self.class.mutable
+        if respond_to?("#{key}=")
-          @mutations[key] = val
+          public_send("#{key}=", val)
         elsif respond_to? key
-          raise Errors::DropMutationException, "Key #{key} cannot be set in the drop."
+          if self.class.mutable
+            @mutations[key] = val
+          else
+            raise Errors::DropMutationException, "Key #{key} cannot be set in the drop."
+          end
         else
           fallback_data[key] = val
         end