When using the normal upload form with a too long filename the Upload form (not Upload wizard) fails to deal with this. Instead you get an ever looping loading symbol.
In fact if you try to change the filename you get a second loading symbol. (Which disappears if new filename is short enough)
The debug console output is:
Uncaught Error: Unable to parse mediawiki.Title.js:24 Title mediawiki.Title.js:24 window.wgUploadWarningObj.uploadWarning.timeout mediawiki.special.upload.js:66 window.wgUploadWarningObj.uploadWarning.checkNow mediawiki.special.upload.js:54 (anonymous function) mediawiki.special.upload.js:149 jQuery.event.dispatch load.php?debug=true&lang=sv&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=20150113T…:4665 elemData.handle load.php?debug=true&lang=sv&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=20150113T…:4333
To recreate:
- Go to Special:Upload&uploadformstyle=basic
- Select any png image not already on Commons
- Set the name to something with more than 256 characters (e.g. "Stora Kopparbärgz grufva – efter sin rätta längd och bredd geometrice afsatt ther iämpte orthernes högd och diupheet warder medh påtäcknade bookstäfvers förklaringh tillkienna gifven, afmäten och rijtat a.o 1662 - Kungliga Bisdasdasdasdasdasdassblioteket.png")