set GO111MODULE=off when installing tools

autoload/go/util.vim

@@ -519,6 +519,37 @@ function! go#util#ShowInfo(info)
   echo "vim-go: " | echohl Function | echon a:info | echohl None
 endfunction
 
+" go#util#SetEnv takes the name of an environment variable and what its value
+" should be and returns a function that will restore it to its original value.
+function! go#util#SetEnv(name, value) abort
+  let l:state = {}
+
+  if len(a:name) == 0
+    return function('s:noop', [], l:state)
+  endif
+
+  let l:remove = 0
+  if exists('$' . a:name)
+    let l:oldvalue = eval('$' . a:name)
+  else
+    let l:remove = 1
+  endif
+
+  call execute('let $' . a:name . ' = "' . a:value . '"')
+
+  if l:remove
+    function! s:remove(name) abort
+      call execute('unlet $' . a:name)
+    endfunction
+    return function('s:remove', [a:name], l:state)
+  endif
+
+  return function('go#util#SetEnv', [a:name, l:oldvalue], l:state)
+endfunction
+
+function! s:noop(...) abort dict
+endfunction
+
 " restore Vi compatibility settings
 let &cpo = s:cpo_save
 unlet s:cpo_save

plugin/go.vim

@@ -101,11 +101,11 @@ function! s:GoInstallBinaries(updateBinaries, ...)
   " change $GOBIN so go get can automatically install to it
   let $GOBIN = go_bin_path
 
-  " old_path is used to restore users own path
-  let old_path = $PATH
-
   " vim's executable path is looking in PATH so add our go_bin path to it
-  let $PATH = go_bin_path . go#util#PathListSep() . $PATH
+  let Restore_path = go#util#SetEnv('PATH', go_bin_path . go#util#PathListSep() . $PATH)
+
+  " GO111MODULE must be off to install golanci-lint and gometalinter
+  let Restore_modules = go#util#SetEnv('GO111MODULE', 'off')
 
   " when shellslash is set on MS-* systems, shellescape puts single quotes
   " around the output string. cmd on Windows does not handle single quotes
@@ -185,7 +185,9 @@ function! s:GoInstallBinaries(updateBinaries, ...)
   endfor
 
   " restore back!
-  let $PATH = old_path
+  call call(Restore_path, [])
+  call call(Restore_modules, [])
+
   if resetshellslash
     set shellslash
   endif