Add syntastic syntax checker using swiftpm

This allows projects using swift package manager to get inline errors
with syntastic.

You can customize the main executable, or the arguments passed to it,
through global configuration variables.

Author: keith

syntax_checkers/swift/swiftpm.vim

@@ -0,0 +1,44 @@
+if exists('g:loaded_syntastic_swift_swiftpm_checker')
+  finish
+endif
+let g:loaded_syntastic_swift_swiftpm_checker = 1
+
+if !exists('g:syntastic_swift_swiftpm_executable')
+  let g:syntastic_swift_swiftpm_executable = 'swift'
+endif
+
+if !exists('g:syntastic_swift_swiftpm_arguments')
+  let g:syntastic_swift_swiftpm_arguments = 'build'
+endif
+
+let s:save_cpo = &cpo
+set cpo&vim
+
+function! SyntaxCheckers_swift_swiftpm_IsAvailable() dict
+  if !executable(self.getExec())
+    return 0
+  endif
+
+  return filereadable('Package.swift')
+endfunction
+
+function! SyntaxCheckers_swift_swiftpm_GetLocList() dict
+  let makeprg = self.makeprgBuild({
+        \ 'fname': '',
+        \ 'args': g:syntastic_swift_swiftpm_arguments })
+
+  let errorformat =
+        \ '%f:%l:%c: error: %m'
+
+  return SyntasticMake({
+        \ 'makeprg': makeprg,
+        \ 'errorformat': errorformat })
+endfunction
+
+call g:SyntasticRegistry.CreateAndRegisterChecker({
+    \ 'filetype': 'swift',
+    \ 'name': 'swiftpm',
+    \ 'exec': g:syntastic_swift_swiftpm_executable })
+
+let &cpo = s:save_cpo
+unlet s:save_cpo