Add metalinter options

1. Add the option to run the metalinter on save
2. Add the option to limit the output to the currently active buffer

There is a outstanding PR with the `gometalinter` repo to add some
needed logic for this:
alecthomas/gometalinter#71 So I assume this PR
should not be merged before that one is merged.

Also this the first vimscript code I’ve ever written, so I guess this
could be done a little cleaner. Especially the implementation of the
`go#lint#GometaAutoSave` func doesn’t feel all that clean to me, but
I’m not sure how to do this in a different/better way. So if you have

autoload/go/lint.vim

@@ -2,6 +2,10 @@ if !exists("g:go_metalinter_command")
     let g:go_metalinter_command = ""
 endif
 
+if !exists("g:go_metalinter_autosave_enabled")
+    let g:go_metalinter_autosave_enabled = ['vet', 'golint']
+endif
+
 if !exists("g:go_metalinter_enabled")
     let g:go_metalinter_enabled = ['vet', 'golint', 'errcheck']
 endif
@@ -18,32 +22,35 @@ if !exists("g:go_errcheck_bin")
     let g:go_errcheck_bin = "errcheck"
 endif
 
-function! go#lint#Gometa(...) abort
+function! go#lint#Gometa(autosave, ...) abort
     if a:0 == 0
         let goargs = expand('%:p:h')
     else
         let goargs = go#util#Shelljoin(a:000)
     endif
 
     let meta_command = "gometalinter --disable-all"
-    if empty(g:go_metalinter_command)
+    if a:autosave || empty(g:go_metalinter_command)
         let bin_path = go#path#CheckBinPath("gometalinter")
         if empty(bin_path)
             return
         endif
 
-        if empty(g:go_metalinter_enabled)
-            echohl Error | echomsg "vim-go: please enable linters with the setting g:go_metalinter_enabled" | echohl None
-            return
+        if a:autosave
+            " include only messages for the active buffer
+            let meta_command .= " --include='^" . expand('%:p') . ".*$'"
         endif
 
-        for linter in g:go_metalinter_enabled
+        " linters
+        let linters = a:autosave ? g:go_metalinter_autosave_enabled : g:go_metalinter_enabled
+        for linter in linters
             let meta_command .= " --enable=".linter
         endfor
 
         " deadline
         let meta_command .= " --deadline=" . g:go_metalinter_deadline
 
+        " path
         let meta_command .=  " " . goargs
     else
         " the user wants something else, let us use it.
@@ -73,7 +80,10 @@ function! go#lint#Gometa(...) abort
 
         let errors = go#list#Get()
         call go#list#Window(len(errors))
-        call go#list#JumpToFirst()
+
+        if !a:autosave
+            call go#list#JumpToFirst()
+        endif
     endif
 endfunction
 

doc/vim-go.txt

@@ -864,7 +864,20 @@ Adds custom text objects. By default it's enabled. >
 
 	let g:go_textobj_enabled = 1
 <
+                                                 *'g:go_metalinter_autosave'*
 
+Use this option to auto |:GoMetaLinter| on save. Only linter messages for
+the active buffer will be shown. By default it's disabled >
+
+  let g:go_metalinter_autosave = 0
+<
+                                         *'g:go_metalinter_autosave_enabled'*
+
+Specifies the enabled linters for auto |GoMetaLinter| on save. By
+default it's using `vet` and `golint`
+>
+  let g:go_metalinter_autosave_enabled = ['vet', 'golint']
+<
                                                   *'g:go_metalinter_enabled'*
 
 Specifies the currently enabled linters for the |GoMetaLinter| command. By

ftplugin/go/commands.vim

@@ -48,7 +48,7 @@ command! -nargs=1 -bang -complete=customlist,go#package#Complete GoImport call g
 command! -nargs=* -bang -complete=customlist,go#package#Complete GoImportAs call go#import#SwitchImport(1, <f-args>, '<bang>')
 
 " -- linters
-command! -nargs=* GoMetaLinter call go#lint#Gometa(<f-args>)
+command! -nargs=* GoMetaLinter call go#lint#Gometa(0, <f-args>)
 command! -nargs=* GoLint call go#lint#Golint(<f-args>)
 command! -nargs=* -bang GoVet call go#lint#Vet(<bang>0, <f-args>)
 command! -nargs=* -complete=customlist,go#package#Complete GoErrCheck call go#lint#Errcheck(<f-args>)

ftplugin/go/mappings.vim

@@ -46,7 +46,7 @@ nnoremap <silent> <Plug>(go-doc-vertical) :<C-u>call go#doc#Open("vnew", "vsplit
 nnoremap <silent> <Plug>(go-doc-split) :<C-u>call go#doc#Open("new", "split")<CR>
 nnoremap <silent> <Plug>(go-doc-browser) :<C-u>call go#doc#OpenBrowser()<CR>
 
-nnoremap <silent> <Plug>(go-metalinter) :<C-u>call go#lint#Gometa('')<CR>
+nnoremap <silent> <Plug>(go-metalinter) :<C-u>call go#lint#Gometa(0)<CR>
 nnoremap <silent> <Plug>(go-vet) :<C-u>call go#lint#Vet(!g:go_jump_to_error)<CR>
 
 

plugin/go.vim

@@ -133,6 +133,11 @@ augroup vim-go
         autocmd BufWritePre *.go call go#fmt#Format(-1)
     endif
 
+    " run gometalinter on save
+    if get(g:, "go_metalinter_autosave", 0)
+        autocmd BufWritePost *.go call go#lint#Gometa(1)
+    endif
+
 augroup END