How to forward multiple arguments from a command in a function?

Question

Given this small vimgrep wrapper, how would I forward multiple arguments to vimgrep, so they are interpreted as a single argument to vimgrep?

command! -nargs=1 FIND call SimpleGrep(<f-args>)
nnoremap <M-f> :FIND<SPACE>

function! SimpleGrep(exp)
    " Depends on: https://github.com/dbakker/vim-projectroot
    let l:base = ProjectRootGuess()
    " Find files with the current extension in project path.
    let l:root = l:base . "/**/*." . expand('%:e')
    execute 'vimgrep' a:exp l:root
endfunc

Currently FIND text works, but FIND "some text" only works when quoted.

Answer 1

The simple case

Projectroot provides the :ProjectRootExe command which can simplify this task greatly.

command! -nargs=+ FIND ProjectRootExe execute "vimgrep /<args>/ **/*." . expand('%:e')
nnoremap <M-f> :FIND<SPACE>

The <args> expands to the arguments supplied to your :FIND command. While -nargs=+ means this command can take at least 1 argument. Since you do not want to quote the search pattern we will add /'s as suggested by :h :vimgrep.

Using <q-args>

Since you wanted to use a function to do some extra logic, you can use <q-args> to slurp up all the arguments into a "quoted string". e.g.

function s:simple_grep(pattern)
  let filetypes = {}
  let filetypes['c'] = '{c,cpp,h}'
  execute "ProjectRootExe vimgrep /" . a:pattern . "/ *." . get(filetypes, &filetype, expand('%:e'))
endfunction

command! -nargs=+ Find call <SID>simple_grep(<q-args>)
nnoremap <M-f> :FIND<SPACE>

I have added some logic to search multiple extensions when using the 'filetype' is set to c.

Alternatives

If you use git and fugitive.vim you may want to look into using :Ggrep as it much faster than :vimgrep and automatically searching from the root of a git project by default.

You may also want to look into using a tool like Ag the silver searcher which searches recursively by default an can be supplied a file type, e.g. ag --js 'pattern'. Note: ag does not search from project root. Settings from man ag:

set grepprg=ag\ --vimgrep\ $*
set grepformat=%f:%l:%c:%m

Now you can use ag powered grep: :grep 'pattern'.

For more help see

:h :command-nargs
:h <args>
:h :vimgrep
:h :execute
:h expand()
:h <q-args>
:h get()
:h projectroot-:ProjectRootExe

Note: I do not use projectroot nor have I tested any of the code above. Use as is.