term: add an option to reuse terminal windows

Closes #2510

autoload/go/config.vim

@@ -53,6 +53,10 @@ function! go#config#TermCloseOnExit() abort
   return get(g:, 'go_term_close_on_exit', 1)
 endfunction
 
+function! go#config#TermReuse() abort
+  return get(g:, 'go_term_reuse', 0)
+endfunction
+
 function! go#config#SetTermCloseOnExit(value) abort
   let g:go_term_close_on_exit = a:value
 endfunction

autoload/go/term.vim

@@ -2,6 +2,8 @@
 let s:cpo_save = &cpo
 set cpo&vim
 
+let s:bufnameprefix = 'goterm://'
+
 " new creates a new terminal with the given command. Mode is set based on the
 " global variable g:go_term_mode, which is by default set to :vsplit
 function! go#term#new(bang, cmd, errorformat) abort
@@ -15,6 +17,10 @@ function! go#term#newmode(bang, cmd, errorformat, mode) abort
     let l:mode = go#config#TermMode()
   endif
 
+  if go#config#TermReuse()
+    call s:closeterm()
+  endif
+
   let l:state = {
         \ 'cmd': a:cmd,
         \ 'bang' : a:bang,
@@ -48,6 +54,7 @@ function! go#term#newmode(bang, cmd, errorformat, mode) abort
         \ }
     let l:state.id = termopen(a:cmd, l:job)
     let l:state.termwinid = win_getid(winnr())
+    let s:lasttermwinid = l:state.termwinid
     call go#util#Chdir(l:dir)
 
     " resize new term if needed.
@@ -66,18 +73,24 @@ function! go#term#newmode(bang, cmd, errorformat, mode) abort
 
   " setup term for vim8
   elseif has('terminal')
+    " Not great randomness, but "good enough" for our purpose here.
+    let l:rnd = sha256(printf('%s%s', reltimestr(reltime()), fnamemodify(bufname(''), ":p")))
+    let l:termname = printf("%s%s", s:bufnameprefix, l:rnd)
+
     let l:term = {
           \ 'out_cb': function('s:out_cb', [], state),
           \ 'exit_cb' : function('s:exit_cb', [], state),
           \ 'curwin': 1,
+          \ 'term_name': l:termname,
         \ }
 
     if l:mode =~ "vertical" || l:mode =~ "vsplit" || l:mode =~ "vnew"
-          let l:term["vertical"] = l:mode
+      let l:term["vertical"] = l:mode
     endif
 
     let l:state.id = term_start(a:cmd, l:term)
     let l:state.termwinid = win_getid(bufwinnr(l:state.id))
+    let s:lasttermwinid = l:state.termwinid
     call go#util#Chdir(l:dir)
 
     " resize new term if needed.
@@ -217,6 +230,43 @@ function! go#term#ToggleCloseOnExit() abort
   return
 endfunction
 
+function! s:closeterm()
+  if !exists('s:lasttermwinid')
+    return
+  endif
+
+  try
+    let l:termwinid = s:lasttermwinid
+    unlet s:lasttermwinid
+    let l:info = getwininfo(l:termwinid)
+    if empty(l:info)
+      return
+    endif
+
+    let l:info = l:info[0]
+
+    if !get(l:info, 'terminal', 0) is 1
+      return
+    endif
+
+    if has('nvim')
+      if 'goterm' == nvim_buf_get_option(nvim_win_get_buf(l:termwinid), 'filetype')
+        call nvim_win_close(l:termwinid, v:true)
+      endif
+      return
+    endif
+
+    if stridx(bufname(winbufnr(l:termwinid)), s:bufnameprefix, 0) == 0
+      let l:winid = win_getid()
+      call win_gotoid(l:termwinid)
+      close!
+      call win_gotoid(l:winid)
+    endif
+  catch
+    call go#util#EchoError(printf("vim-go: %s" v:exception))
+  endtry
+endfunction
+
 " restore Vi compatibility settings
 let &cpo = s:cpo_save
 unlet s:cpo_save

doc/vim-go.txt

@@ -1716,6 +1716,13 @@ The default command used to open a new terminal for go commands such as
 Applicable to Neovim and Vim with `terminal` feature only.
 >
   let g:go_term_mode = "vsplit"
+<
+                                                          *'g:go_term_reuse'*
+
+Reuse the terminal window when |g:go_term_enabled| is set. By default it's
+disabled.
+>
+  let g:go_term_reuse = 0
 <
                                                           *'g:go_term_height'*
                                                            *'g:go_term_width'*