Fix #4075: Make sure that .jekyll-metadata is not generated when not needed.

lib/jekyll/regenerator.rb

@@ -130,7 +130,9 @@ module Jekyll
     #
     # Returns nothing.
     def write_metadata
-      File.binwrite(metadata_file, Marshal.dump(metadata))
+      unless disabled?
+        File.binwrite(metadata_file, Marshal.dump(metadata))
+      end
     end
 
     # Produce the absolute path of the metadata file

test/test_regenerator.rb

@@ -305,4 +305,23 @@ class TestRegenerator < JekyllUnitTest
       assert @regenerator.modified?(@path)
     end
   end
+
+  context "when incremental regen is disabled" do
+    setup do
+      FileUtils.rm_rf(source_dir(".jekyll-metadata"))
+      @site = Site.new(Jekyll.configuration({
+        "source" => source_dir,
+        "destination" => dest_dir,
+        "incremental" => false
+      }))
+
+      @site.process
+      @path = @site.in_source_dir(@site.pages.first.path)
+      @regenerator = @site.regenerator
+    end
+
+    should "not create .jekyll-metadata" do
+      refute File.file?(source_dir(".jekyll-metadata"))
+    end
+  end
 end