Spotted in production:
153 Not a valid stream resource in /srv/mediawiki/php-1.25wmf21/includes/GlobalFunctions.php on line 3196 153 Not a valid stream resource in /srv/mediawiki/php-1.25wmf21/includes/GlobalFunctions.php on line 3188
Happens when popen( $cmd, 'r' ); a few lines up fails to return a handle.
https://gerrit.wikimedia.org/r/#/c/198785/ by @MaxSem deprecated wfDiff() in favor of DiffEngine/UnifiedDiffFormatter and also did:
$h = popen( $cmd, 'r' ); + if ( !$h ) { + unlink( $oldtextName ); + unlink( $newtextName ); + throw new Exception( __METHOD__ . '(): popen() failed' ); + }
Seems to handle the case.