Revert "provider: delete vimL stderr collector, now that it exists builtin"

This change exposed a memory issue with buffered channels, possibly
involving GC. Revert until it has been fixed.

This reverts commit 0de019b6a6.

runtime/autoload/provider.vim

@@ -0,0 +1,20 @@
+" Common functionality for providers
+
+let s:stderr = {}
+
+function! provider#stderr_collector(chan_id, data, event)
+   let stderr = get(s:stderr, a:chan_id, [''])
+   let stderr[-1] .= a:data[0]
+   call extend(stderr, a:data[1:])
+   let s:stderr[a:chan_id] = stderr
+endfunction
+
+function! provider#clear_stderr(chan_id)
+  if has_key(s:stderr, a:chan_id)
+    call remove(s:stderr, a:chan_id)
+  endif
+endfunction
+
+function! provider#get_stderr(chan_id)
+   return get(s:stderr, a:chan_id, [])
+endfunction

runtime/autoload/provider/clipboard.vim

@@ -7,7 +7,7 @@ let s:clipboard = {}
 
 " When caching is enabled, store the jobid of the xclip/xsel process keeping
 " ownership of the selection, so we know how long the cache is valid.
-let s:selection = { 'owner': 0, 'data': [], 'stderr_buffered': v:true }
+let s:selection = { 'owner': 0, 'data': [], 'on_stderr': function('provider#stderr_collector') }
 
 function! s:selection.on_exit(jobid, data, event) abort
   " At this point this nvim instance might already have launched
@@ -16,10 +16,12 @@ function! s:selection.on_exit(jobid, data, event) abort
     let self.owner = 0
   endif
   if a:data != 0
+    let stderr = provider#get_stderr(a:jobid)
     echohl WarningMsg
-    echomsg 'clipboard: error invoking '.get(self.argv, 0, '?').': '.join(self.stderr)
+    echomsg 'clipboard: error invoking '.get(self.argv, 0, '?').': '.join(stderr)
     echohl None
   endif
+  call provider#clear_stderr(a:jobid)
 endfunction
 
 let s:selections = { '*': s:selection, '+': copy(s:selection) }

runtime/autoload/provider/node.vim

@@ -3,7 +3,7 @@ if exists('g:loaded_node_provider')
 endif
 let g:loaded_node_provider = 1
 
-let s:job_opts = {'rpc': v:true, 'stderr_buffered': v:true}
+let s:job_opts = {'rpc': v:true, 'on_stderr': function('provider#stderr_collector')}
 
 function! provider#node#Detect() abort
   return has('win32') ? exepath('neovim-node-host.cmd') : exepath('neovim-node-host')
@@ -32,18 +32,19 @@ function! provider#node#Require(host) abort
   endif
 
   try
-    let job = copy(s:job_opts)
-    let channel_id = jobstart(args, job)
+    let channel_id = jobstart(args, s:job_opts)
     if rpcrequest(channel_id, 'poll') ==# 'ok'
       return channel_id
     endif
   catch
     echomsg v:throwpoint
     echomsg v:exception
-    for row in job.stderr
+    for row in provider#get_stderr(channel_id)
       echomsg row
     endfor
   endtry
+  finally
+    call provider#clear_stderr(channel_id)
   endtry
   throw remote#host#LoadErrorForHost(a:host.orig_name, '$NVIM_NODE_LOG_FILE')
 endfunction

runtime/autoload/provider/pythonx.vim

@@ -5,7 +5,7 @@ endif
 
 let s:loaded_pythonx_provider = 1
 
-let s:job_opts = {'rpc': v:true, 'stderr_buffered': v:true}
+let s:job_opts = {'rpc': v:true, 'on_stderr': function('provider#stderr_collector')}
 
 function! provider#pythonx#Require(host) abort
   let ver = (a:host.orig_name ==# 'python') ? 2 : 3
@@ -21,17 +21,18 @@ function! provider#pythonx#Require(host) abort
   endfor
 
   try
-    let job = copy(s:job_opts)
-    let channel_id = jobstart(args, job)
+    let channel_id = jobstart(args, s:job_opts)
     if rpcrequest(channel_id, 'poll') ==# 'ok'
       return channel_id
     endif
   catch
     echomsg v:throwpoint
     echomsg v:exception
-    for row in job.stderr
+    for row in provider#get_stderr(channel_id)
       echomsg row
     endfor
+  finally
+    call provider#clear_stderr(channel_id)
   endtry
   throw remote#host#LoadErrorForHost(a:host.orig_name,
         \ '$NVIM_PYTHON_LOG_FILE')