Revert to previous partial symbol on autocomplete (#5)

This change handles issue reported on lite-xl/lite-xl-lsp#67
by restoring previous partial since the completion request is async
and new text could have been written by user while handling the 
LSP server response, which can result in invalid insert positions for 
the received completion items.

Depends on pragtical/pragtical#66

init.lua

@@ -551,6 +551,16 @@ local function autocomplete_onselect(index, item)
   local dv = get_active_docview()
   if completion.textEdit then
     if dv then
+      -- Restore previous partial since the complete request is async and
+      -- new text could have been written while retrieving autocomplete items
+      -- which results in invalid insert positions if we don't revert partial
+      local current_partial = {autocomplete.get_partial_symbol()}
+      if current_partial[1] ~= item.data.partial[1] then
+        local partial, pl1, pc1, pl2, pc2 = table.unpack(current_partial)
+        dv.doc:remove(pl1, pc1, pl2, pc2)
+        partial, pl1, pc1 = table.unpack(item.data.partial)
+        dv.doc:insert(pl1, pc1, partial)
+      end
       local is_snippet = completion.insertTextFormat
         and completion.insertTextFormat == protocol.InsertTextFormat.Snippet
       local edit_applied = apply_edit(
@@ -587,8 +597,7 @@ local function autocomplete_onselect(index, item)
     ---@type core.doc
     local doc = dv.doc
     if dv then
-      local line2, col2 = doc:get_selection()
-      local line1, col1 = doc:position_offset(line2, col2, translate.start_of_word)
+      local _, line1, col1, line2, col2 = autocomplete.get_partial_symbol()
       doc:set_selection(line1, col1, line2, col2)
       snippets.execute {format = 'lsp', template = completion.insertText}
       return true
@@ -1402,6 +1411,8 @@ function lsp.request_completion(doc, line, col, forced)
         return false
       end
 
+      local partial = { autocomplete.get_partial_symbol() }
+
       server:push_request('textDocument/completion', {
         params = request,
         overwrite = true,
@@ -1511,7 +1522,9 @@ function lsp.request_completion(doc, line, col, forced)
               info = info,
               desc = desc,
               data = {
-                server = server, completion_item = symbol
+                server = server,
+                completion_item = symbol,
+                partial = partial
               },
               onselect = autocomplete_onselect
             }