gitweb: Add invisible hyperlink to from-file/to-file diff header

Change replacing hashes as from-file/to-file with filenames from
difftree to adding invisible (except underlining on hover/mouseover)
hyperlink to from-file/to-file blob.  /dev/null as from-file or
to-file is not changed (is not hyperlinked).

This makes two-file from-file/to-file unified diff header parsing in
git_patchset_body more generic, and not only for legacy blobdiffs.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.css

@@ -273,11 +273,21 @@ td.mode {
 	font-family: monospace;
 }
 
+div.diff a.list {
+	text-decoration: none;
+}
+
+div.diff a.list:hover {
+	text-decoration: underline;
+}
+
+div.diff.to_file a.list,
 div.diff.to_file,
 div.diff.add {
 	color: #008800;
 }
 
+div.diff.from_file a.list,
 div.diff.from_file,
 div.diff.rem {
 	color: #cc0000;

gitweb/gitweb.perl

@@ -1711,8 +1711,11 @@ sub git_patchset_body {
 
 			my $file = $diffinfo->{'from_file'};
 			$file  ||= $diffinfo->{'file'};
-			$patch_line =~ s|a/[0-9a-fA-F]{40}|a/$file|g;
-			print "<div class=\"diff from_file\">" . esc_html($patch_line) . "</div>\n";
+			$file = $cgi->a({-href => href(action=>"blob", hash_base=>$hash_parent,
+			                               hash=>$diffinfo->{'from_id'}, file_name=>$file),
+			                -class => "list"}, esc_html($file));
+			$patch_line =~ s|a/.*$|a/$file|g;
+			print "<div class=\"diff from_file\">$patch_line</div>\n";
 
 			$patch_line = <$fd>;
 			chomp $patch_line;
@@ -1720,8 +1723,11 @@ sub git_patchset_body {
 			#$patch_line =~ m/^+++/;
 			$file    = $diffinfo->{'to_file'};
 			$file  ||= $diffinfo->{'file'};
-			$patch_line =~ s|b/[0-9a-fA-F]{40}|b/$file|g;
-			print "<div class=\"diff to_file\">" . esc_html($patch_line) . "</div>\n";
+			$file = $cgi->a({-href => href(action=>"blob", hash_base=>$hash,
+			                               hash=>$diffinfo->{'to_id'}, file_name=>$file),
+			                -class => "list"}, esc_html($file));
+			$patch_line =~ s|b/.*|b/$file|g;
+			print "<div class=\"diff to_file\">$patch_line</div>\n";
 
 			next LINE;
 		}