Unlike in Ag.vim, fzf.vim’s :Ag command does not provide the ability to specify additional options to use with The Silver Searcher a.k.a. ag. Unfortunately, fzf does not use --exclude-vcs-ignores by default despite it being useful for programmers i.e. search file contents under a vendor directory or a mount, for example.

The way to do it in fzf.vim is to create a custom command that will pass the -U|--exclude-vcs-ingores to the underlying ag call:

command! -bang -nargs=* Agu call fzf#vim#ag(<q-args>, '--skip-vcs-ignores', {'down': '~40%'})

With this in ~/.vimrc, it is now possible to search the contents of a project by using :Agu instead of :Ag. The search will no longer ignore files that are in .gitignore or any other VCS ignore lists.

See The Silver Searcher and fzf.vim.