RustTest: support optional command modifiers

Examples:

  :topleft RustTest
  :belowright RustTest
  :tab RustTest
  :vert RustTest

See `:h <mods>` for all supported command modifiers.

You can specify multiple modifiers:

  :leftabove vert RustTest

Author: mhinz

autoload/rust.vim

@@ -507,16 +507,16 @@ function! s:SearchTestFunctionNameUnderCursor() abort
     return matchstr(getline(test_func_line), '\m\C^\s*fn\s\+\zs\h\w*')
 endfunction
 
-function! rust#Test(all, options) abort
+function! rust#Test(mods, all, options) abort
     let manifest = findfile('Cargo.toml', expand('%:p:h') . ';')
     if manifest ==# ''
         return rust#Run(1, '--test ' . a:options)
     endif
 
     if has('terminal')
-        let cmd = 'terminal '
+        let cmd = printf('%s terminal ', a:mods)
     elseif has('nvim')
-        let cmd = 'noautocmd new | terminal '
+        let cmd = printf('%s noautocmd new | terminal ', a:mods)
     else
         let cmd = '!'
         let manifest = shellescape(manifest)

ftplugin/rust.vim

@@ -136,7 +136,7 @@ command! -bar RustInfoToClipboard call rust#debugging#InfoToClipboard()
 command! -bar -nargs=1 RustInfoToFile call rust#debugging#InfoToFile(<f-args>)
 
 " See |:RustTest| for docs
-command! -buffer -nargs=* -bang RustTest call rust#Test(<bang>0, <q-args>)
+command! -buffer -nargs=* -bang RustTest call rust#Test(<q-mods>, <bang>0, <q-args>)
 
 if !exists("b:rust_last_rustc_args") || !exists("b:rust_last_args")
     let b:rust_last_rustc_args = []