gitweb: Give side-by-side diff extra CSS styling

Use separate background colors for pure removal, pure addition and
change for side-by-side diff.  This makes reading such diff easier,
allowing to easily distinguish empty lines in diff from vertical
whitespace used to align chunk blocks.

Note that if lines in diff were numbered, the absence of line numbers
[for one side] would help in distinguishing empty lines from vertical
align.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -4890,7 +4890,7 @@ sub print_sidebyside_diff_chunk {
 		# empty contents block on start rem/add block, or end of chunk
 		if (@ctx && (!$class || $class eq 'rem' || $class eq 'add')) {
 			print join '',
-				'<div class="chunk_block">',
+				'<div class="chunk_block ctx">',
 					'<div class="old">',
 					@ctx,
 					'</div>',
@@ -4902,15 +4902,34 @@ sub print_sidebyside_diff_chunk {
 		}
 		# empty add/rem block on start context block, or end of chunk
 		if ((@rem || @add) && (!$class || $class eq 'ctx')) {
-			print join '',
-				'<div class="chunk_block">',
-					'<div class="old">',
-					@rem,
-					'</div>',
-					'<div class="new">',
-					@add,
-					'</div>',
-				'</div>';
+			if (!@add) {
+				# pure removal
+				print join '',
+					'<div class="chunk_block rem">',
+						'<div class="old">',
+						@rem,
+						'</div>',
+					'</div>';
+			} elsif (!@rem) {
+				# pure addition
+				print join '',
+					'<div class="chunk_block add">',
+						'<div class="new">',
+						@add,
+						'</div>',
+					'</div>';
+			} else {
+				# assume that it is change
+				print join '',
+					'<div class="chunk_block chg">',
+						'<div class="old">',
+						@rem,
+						'</div>',
+						'<div class="new">',
+						@add,
+						'</div>',
+					'</div>';
+			}
 			@rem = @add = ();
 		}
 

gitweb/static/gitweb.css

@@ -491,6 +491,19 @@ div.chunk_block div.new {
 	width: 50%;
 }
 
+div.chunk_block.rem div.old div.diff.rem {
+	background-color: #fff5f5;
+}
+div.chunk_block.add div.new div.diff.add {
+	background-color: #f8fff8;
+}
+div.chunk_block.chg div     div.diff {
+	background-color: #fffff0;
+}
+div.chunk_block.ctx div     div.diff.ctx {
+	color: #404040;
+}
+
 
 div.index_include {
 	border: solid #d9d8d1;