how do I ignore a directory for diff

Hello,

I have been looking into ignoring a subdirectory of my tree for diffing with upstream. I'll explain the situation below :

My tree is a fork of an upstream repo. There is a specific directory in my tree lets call it foo/bar that i would like to ignore for diff. This directory includes only files that i added to my repo and is therefore irrelevant for diffing (i know all files in there have been added and are not in upstream). Having there in the diff is just making a lot of files to appear and that is confusing to see what is changed from upstream.

I have read the docs and found a way mentioning that i should add a line to .gitattributes with : foo/bar/* -diff

But this still lists the files in there when i'm diffing.

Is there any way to achieve this ? i cant find any clear explanation in the docs.

Any help would be greatly appreciated :)

Lionel.