Discovered this when wikitech was moved to new server; wikidiff2 had been set up as $wgExternalDiffEngine but the PHP extension hadn't been installed on the new machine.

Diffs failed silently, and were even saved blank into the diff cache. All edits appeared as thought here were no changes, more or less.

Should either show an error message, fall back to regular diff code, or some combination thereof; and should definitely not be saving bogus diffs into the cache!

Version: unspecified
Severity: enhancement