Fix review comments

* Fix auto toggle command
* Add guard agains Go versions lower than 1.11
* Add documentation
* Fixed setting correct filetype
* Fixed parsing errors
* Changed variable names to be consistent

autoload/go/config.vim

@@ -278,12 +278,12 @@ function! go#config#SetAsmfmtAutosave(value) abort
   let g:go_asmfmt_autosave = a:value
 endfunction
 
-function! go#config#ModfmtAutosave() abort
-	return get(g:, "go_modfmt_autosave", 1)
+function! go#config#ModFmtAutosave() abort
+	return get(g:, "go_mod_fmt_autosave", 1)
 endfunction
 
-function! go#config#SetModfmtAutosave(value) abort
-  let g:go_modfmt_autosave = a:value
+function! go#config#SetModFmtAutosave(value) abort
+  let g:go_mod_fmt_autosave = a:value
 endfunction
 
 function! go#config#DocMaxHeight() abort

autoload/go/mod.vim

@@ -1,11 +1,24 @@
+let s:go_major_version = ""
+
 function! go#mod#Format() abort
+  " go mod only exists in `v1.11`
+  if empty(s:go_major_version)
+    let tokens = matchlist(go#util#System("go version"), '\d\+.\(\d\+\) ')
+    let s:go_major_version = str2nr(tokens[1])
+  endif
+
+  if s:go_major_version < "11" 
+    call go#util#EchoError("Go v1.11 is required to format go.mod file")
+    return
+  endif
+
   let fname = fnamemodify(expand("%"), ':p:gs?\\?/?')
 
   " Save cursor position and many other things.
   let l:curw = winsaveview()
 
   " Write current unsaved buffer to a temp file
-  let l:tmpname = tempname() . '.go'
+  let l:tmpname = tempname() . '.mod'
   call writefile(go#util#GetLines(), l:tmpname)
   if go#util#IsWin()
     let l:tmpname = tr(l:tmpname, '\', '/')
@@ -88,13 +101,12 @@ function! s:parse_errors(filename, content) abort
   " list of errors to be put into location list
   let errors = []
   for line in splitted
-    let tokens = matchlist(line, '^\(.\{-}\):\(\d\+\):\(\d\+\)\s*\(.*\)')
+    let tokens = matchlist(line, '^\(.\{-}\):\(\d\+\):\s*\(.*\)')
     if !empty(tokens)
       call add(errors,{
             \"filename": a:filename,
             \"lnum":     tokens[2],
-            \"col":      tokens[3],
-            \"text":     tokens[4],
+            \"text":     tokens[3],
             \ })
     endif
   endfor
@@ -108,21 +120,21 @@ function! s:show_errors(errors) abort
   let l:listtype = go#list#Type("GoModFmt")
   if !empty(a:errors)
     call go#list#Populate(l:listtype, a:errors, 'Format')
-    echohl Error | echomsg "GoModFmt returned error" | echohl None
+    call go#util#EchoError("GoModFmt returned error")
   endif
 
   " this closes the window if there are no errors or it opens
   " it if there is any
   call go#list#Window(l:listtype, len(a:errors))
 endfunction
 
-function! go#mod#ToggleModfmtAutoSave() abort
-  if go#config#ModfmtAutosave()
-    call go#config#SetModfmtAutosave(0)
+function! go#mod#ToggleModFmtAutoSave() abort
+  if go#config#ModFmtAutosave()
+    call go#config#SetModFmtAutosave(0)
     call go#util#EchoProgress("auto mod fmt disabled")
     return
   end
 
-  call go#config#SetModfmtAutosave(1)
-  call go#util#EchoProgress("auto fmt enabled")
+  call go#config#SetModFmtAutosave(1)
+  call go#util#EchoProgress("auto mod fmt enabled")
 endfunction

doc/vim-go.txt

@@ -806,6 +806,11 @@ CTRL-t
 
     Toggles |'g:go_fmt_autosave'|.
 
+                                                     *:GoModFmtAutoSaveToggle*
+:GoModFmtAutoSaveToggle
+
+    Toggles |'g:go_mod_fmt_autosave'|.
+
                                                      *:GoAsmFmtAutoSaveToggle*
 :GoAsmFmtAutoSaveToggle
 
@@ -880,6 +885,13 @@ CTRL-t
           }
       }
 <
+                                                                  *:GoModFmt*
+:GoModFmt
+
+    Filter the current go.mod buffer through "go mod edit -fmt" command.  It
+    tries to preserve cursor position and avoids replacing the buffer with
+    stderr output.
+
 ==============================================================================
 MAPPINGS                                                        *go-mappings*
 
@@ -1097,6 +1109,10 @@ Calls `:GoImport` for the current package
 Generate if err != nil { return ... } automatically which infer the type of
 return values and the numbers.
 
+                                                                *(go-mod-fmt)*
+
+Calls |:GoModFmt| for the current buffer
+
 ==============================================================================
 TEXT OBJECTS                                                 *go-text-objects*
 
@@ -1287,7 +1303,15 @@ doesn't break. However it's slows (creates/deletes a file for every save) and
 it's causing problems on some Vim versions. By default it's disabled. >
 
   let g:go_fmt_experimental = 0
+
 <
+                                                     *'g:go_mod_fmt_autosave'*
+
+Use this option to auto |:GoModFmt| on save. By default it's enabled >
+
+  let g:go_mod_fmt_autosave = 1
+<
+
                                                *'g:go_doc_keywordprg_enabled'*
 
 Use this option to run `godoc` on words under the cursor with |K|; this will
@@ -1497,10 +1521,10 @@ that was called. Supported values are "", "quickfix", and "locationlist".
 Specifies the type of list to use for command outputs (such as errors from
 builds, results from static analysis commands, etc...). When an expected key
 is not present in the dictionary, |'g:go_list_type'| will be used instead.
-Supported keys are "GoBuild", "GoErrCheck", "GoFmt", "GoInstall", "GoLint",
-"GoMetaLinter", "GoMetaLinterAutoSave", "GoModifyTags" (used for both
-:GoAddTags and :GoRemoveTags), "GoRename", "GoRun", and "GoTest".  Supported
-values for each command are "quickfix" and "locationlist".
+Supported keys are "GoBuild", "GoErrCheck", "GoFmt", "GoModFmt", "GoInstall",
+"GoLint", "GoMetaLinter", "GoMetaLinterAutoSave", "GoModifyTags" (used for
+both :GoAddTags and :GoRemoveTags), "GoRename", "GoRun", and "GoTest".
+Supported values for each command are "quickfix" and "locationlist".
 >
   let g:go_list_type_commands = {}
 <
@@ -1874,6 +1898,13 @@ filetype.
 The `gohtmltmpl` filetype is automatically set for `*.tmpl` files; the
 `gotexttmpl` is never automatically set and needs to be set manually.
 
+==============================================================================
+                                                    *gomod* *ft-gomod-syntax*
+go.mod file syntax~
+
+The `gomod` 'filetype' provides syntax highlighting for Go's module file 
+`go.mod`
+
 
 ==============================================================================
 DEBUGGER                                                            *go-debug*

ftdetect/gofiletype.vim

@@ -31,8 +31,9 @@ au BufReadPost *.s call s:gofiletype_post()
 
 au BufRead,BufNewFile *.tmpl set filetype=gohtmltmpl
 
-au BufNewFile *.mod setfiletype gomod | setlocal fileencoding=utf-8 fileformat=unix
-au BufRead *.mod call s:gofiletype_pre("gomod")
-au BufReadPost *.mod call s:gofiletype_post()
+" make sure we explicitly look for a `go.mod` and the `module` starts from the
+" beginning
+au BufNewFile,BufRead go.mod
+	\ if getline(1) =~ '^module.*' | set filetype=gomod |  endif
 
 " vim: sw=2 ts=2 et

ftplugin/gomod/commands.vim

@@ -1 +1,3 @@
 command! -nargs=0 -range GoModFmt call go#mod#Format()
+
+command! -nargs=0 GoModFmtAutoSaveToggle call go#mod#ToggleModFmtAutoSave()

plugin/go.vim

@@ -228,7 +228,7 @@ endfunction
 
 function! s:modfmt_autosave()
   " go.mod code formatting on save
-  if get(g:, "go_modfmt_autosave", 1)
+  if get(g:, "go_mod_fmt_autosave", 1)
     call go#mod#Format()
   endif
 endfunction

syntax/gomod.vim

@@ -38,8 +38,8 @@ highlight default link gomodReplaceOperator Operator
 
 
 " highlight semver, note that this is very simple. But it works for now
-syntax match gomodVersion "v\d\.\d\.\d"
-syntax match gomodVersion "v\d\.\d\.\d-.*"
+syntax match gomodVersion "v\d\+\.\d\+\.\d\+"
+syntax match gomodVersion "v\d\+\.\d\+\.\d\+-.*"
 highlight default link gomodVersion Identifier
 
 let b:current_syntax = "gomod"