My objective is to have some production files ignored on specific branches. Git doesn't allow to do it.
My solution is to make a general .gitignore file and add .gitignore.branch_name files for the branches I want to add specific file exclusion.
I'll use post-checkout hook to copy those .gitignore.branch_name in place of .git/info/exclude each time I go to the branch with git checkout branch_name.