Incrementally regenerate missing destination file

Addresses the third point of #3591, in which the incremental regenerator doesn't notice that destination files have gone missing.

lib/jekyll/regenerator.rb

@@ -18,16 +18,21 @@ module Jekyll
     def regenerate?(document)
       case document
       when Post, Page
-        document.asset_file? || document.data['regenerate'] ||
-          modified?(site.in_source_dir(document.relative_path))
+        return ( document.asset_file? || 
+                 document.data['regenerate'] || 
+                 source_modified_or_dest_missing?(
+                   site.in_source_dir(document.relative_path),
+                   document.destination(@site.dest)) )
       when Document
-        !document.write? || document.data['regenerate'] || modified?(document.path)
+        return ( !document.write? ||
+                document.data['regenerate'] ||
+                source_modified_or_dest_missing?(
+                    document.path, 
+                    document.destination(@site.dest)) )
       else
-        if document.respond_to?(:path)
-          modified?(document.path)
-        else
-          true
-        end
+        source_path = document.respond_to?(:path)        ? document.path                    : nil
+        dest_path   = document.respond_to?(:destination) ? document.destination(@site.dest) : nil
+        return source_modified_or_dest_missing?(source_path, dest_path)
       end
     end
 
@@ -67,6 +72,17 @@ module Jekyll
       @cache = {}
     end
 
+
+    # Checks if the source has been modified or the
+    # destination is missing
+    #
+    # returns a boolean
+    def source_modified_or_dest_missing?(source_path, dest_path)
+      source_modified = source_path ? modified?(source_path)  : true
+      dest_missing    = dest_path   ? !File.exist?(dest_path) : false
+      return source_modified || dest_missing
+    end
+
     # Checks if a path's (or one of its dependencies)
     # mtime has changed
     #

test/test_regenerator.rb

@@ -36,14 +36,50 @@ class TestRegenerator < JekyllUnitTest
       @regenerator.regenerate?(@document)
       @regenerator.regenerate?(@asset_file)
 
+      # we need to create the destinations for these files,
+      # because regenerate? checks if the destination exists
+      [@page, @post, @document, @asset_file].each do |item|
+        if item.respond_to?(:destination) 
+          dest = item.destination(@site.dest)
+          FileUtils.mkdir_p(File.dirname(dest))
+          FileUtils.touch(dest)
+        end
+      end
       @regenerator.write_metadata
       @regenerator = Regenerator.new(@site)
 
+      # these should pass, since nothing has changed, and the
+      # loop above made sure the desinations exist
       assert !@regenerator.regenerate?(@page)
       assert !@regenerator.regenerate?(@post)
       assert !@regenerator.regenerate?(@document)
     end
 
+    should "regenerate if destination missing" do
+      # Process files
+      @regenerator.regenerate?(@page)
+      @regenerator.regenerate?(@post)
+      @regenerator.regenerate?(@document)
+      @regenerator.regenerate?(@asset_file)
+
+      @regenerator.write_metadata
+      @regenerator = Regenerator.new(@site)
+
+      # make sure the files don't actually exist
+      [@page, @post, @document, @asset_file].each do |item|
+        if item.respond_to?(:destination) 
+          dest = item.destination(@site.dest)
+          File.unlink(dest) unless !File.exist?(dest)
+        end
+      end
+
+      # while nothing has changed, the output files were not
+      # generated, so they still need to be regenerated
+      assert @regenerator.regenerate?(@page)
+      assert @regenerator.regenerate?(@post)
+      assert @regenerator.regenerate?(@document)
+    end
+
     should "always regenerate asset files" do
       assert @regenerator.regenerate?(@asset_file)
     end

test/test_site.rb

@@ -495,6 +495,25 @@ class TestSite < JekyllUnitTest
         assert_equal mtime3, mtime4 # no modifications, so remain the same
       end
 
+      should "regnerate files that have had their destination deleted" do
+        contacts_html = @site.pages.find { |p| p.name == "contacts.html" }
+        @site.process
+
+        source = @site.in_source_dir(contacts_html.path)
+        dest = File.expand_path(contacts_html.destination(@site.dest))
+        mtime1 = File.stat(dest).mtime.to_i # first run must generate dest file
+
+        # simulate file modification by user
+        File.unlink dest
+        refute File.exist?(dest)
+
+        sleep 1
+        @site.process
+        assert File.exist?(dest)
+        mtime2 = File.stat(dest).mtime.to_i
+        refute_equal mtime1, mtime2 # must be regenerated 
+      end
+
     end
 
   end