Improve trigger completion (nvim-lua#195)

* Added smart tab functions and mappings

* Remove unneeded vim functions

* Adjust documentation

* As requested re-adding vim functions

For backwards compatibility purposes

* Mention new functions in readme

* Mention new function in help as well

* Added also documentation and mapping for trigger

* Bonus: use new vim.b feature

With the new api `vim.b` you can get and set buffer variables directly
Also add deprecated comment to vim functions

README.md

@@ -101,21 +101,15 @@ let g:completion_enable_auto_popup = 0
 - You can manually trigger completion with mapping key by
 
 ```vim
-inoremap <silent><expr> <c-p> completion#trigger_completion() "map <c-p> to manually trigger completion
+"map <c-p> to manually trigger completion
+imap <silent> <c-p> <Plug>(completion_trigger)
 ```
 
 - Or you want to use `<Tab>` as trigger keys
 
 ```vim
-function! s:check_back_space() abort
-    let col = col('.') - 1
-    return !col || getline('.')[col - 1]  =~ '\s'
-endfunction
-
-inoremap <silent><expr> <TAB>
-  \ pumvisible() ? "\<C-n>" :
-  \ <SID>check_back_space() ? "\<TAB>" :
-  \ completion#trigger_completion()
+nmap <tab> <Plug>(completion_smart_tab)
+nmap <s-tab> <Plug>(completion_smart_s_tab)
 ```
 
 ### Enable Snippets Support

autoload/completion.vim

@@ -14,17 +14,20 @@ function! completion#wrap_completion() abort
     endif
 endfunction
 
+" Depracated
 " Wrapper to get manually trigger working
 " Please send me a pull request if you know how to do this properly...
 function! completion#completion_wrapper()
     lua require'completion'.triggerCompletion()
     return ''
 endfunction
 
+" Depracated
 function! completion#trigger_completion()
     return "\<c-r>=completion#completion_wrapper()\<CR>"
 endfunction
 
+" Depracated
 " Wrapper of getting buffer variable
 " Avoid accessing to unavailable variable
 function! completion#get_buffer_variable(str)

doc/completion-nvim.txt

@@ -66,20 +66,13 @@ g:completion_enable_auto_popup               *g:completion_enable_auto_popup*
 	mapping keys. For example: 
 >
         " map <c-p> to manually trigger completion 
-        inoremap <silent><expr> <c-p> completion#trigger_completion()
+        imap <silent> <c-p> <Plug>(completion_trigger)
 <
         Or you want to use <tab> to trigger completion without modifying the
         usage to <tab> keys.
 >
-        function! s:check_back_space() abort
-            let col = col('.') - 1
-            return !col || getline('.')[col - 1]  =~ '\s'
-        endfunction
-
-        inoremap <silent><expr> <TAB>
-            \ pumvisible() ? "\<C-n>" :
-            \ <SID>check_back_space() ? "\<TAB>" :
-            \ completion#trigger_completion()
+	nmap <tab> <Plug>(completion_smart_tab)
+	nmap <s-tab> <Plug>(completion_smart_s_tab)
 <
 
         default value: 1

lua/completion.lua

@@ -34,16 +34,43 @@ M.triggerCompletion = function()
 end
 
 M.completionToggle = function()
-  local enable = api.nvim_call_function('completion#get_buffer_variable', {'completion_enable'})
+  local enable = vim.b.completion_enable
   if enable == nil then
     M.on_attach()
   elseif enable == 0 then
-    api.nvim_buf_set_var(0, 'completion_enable', 1)
+    vim.b.completion_enable = 1
   else
-    api.nvim_buf_set_var(0, 'completion_enable', 0)
+    vim.b.completion_enable = 0
   end
 end
 
+------------------------------------------------------------------------
+--                         smart tab                                  --
+------------------------------------------------------------------------
+
+function M.smart_tab()
+  if vim.fn.pumvisible() ~= 0 then
+    api.nvim_eval([[feedkeys("\<c-n>", "n")]])
+    return
+  end
+
+  local col = vim.fn.col('.') - 1
+  if col == 0 or vim.fn.getline('.'):sub(col, col):match('%s') then
+    api.nvim_eval([[feedkeys("\<tab>", "n")]])
+    return
+  end
+
+  source.triggerCompletion(true, manager)
+end
+
+function M.smart_s_tab()
+  if vim.fn.pumvisible() ~= 0 then
+    api.nvim_eval([[feedkeys("\<c-p>", "n")]])
+    return
+  end
+
+  api.nvim_eval([[feedkeys("\<s-tab>", "n")]])
+end
 
 ------------------------------------------------------------------------
 --                         confirm completion                         --
@@ -132,7 +159,7 @@ end
 
 -- TODO: need further refactor, very messy now:(
 function M.on_InsertEnter()
-  local enable = api.nvim_call_function('completion#get_buffer_variable', {'completion_enable'})
+  local enable = vim.b.completion_enable
   if enable == nil or enable == 0 then
     return
   end
@@ -235,7 +262,7 @@ M.on_attach = function(option)
       api.nvim_command("autocmd!")
     api.nvim_command("augroup end")
   end
-  api.nvim_buf_set_var(0, 'completion_enable', 1)
+  vim.b.completion_enable = 1
 end
 
 return M

plugin/completion.vim

@@ -122,6 +122,15 @@ inoremap <silent> <Plug>(completion_next_source)
 inoremap <silent> <Plug>(completion_prev_source)
       \ <cmd>lua require'completion'.prevSource()<CR>
 
+inoremap <silent> <Plug>(completion_smart_tab)
+      \ <cmd>lua require'completion'.smart_tab()<CR>
+
+inoremap <silent> <Plug>(completion_smart_s_tab)
+      \ <cmd>lua require'completion'.smart_s_tab()<CR>
+
+inoremap <silent> <Plug>(completion_trigger)
+      \ <cmd>lua require'completion'.triggerCompletion()<CR>
+
 command! -nargs=0 CompletionToggle  lua require'completion'.completionToggle()
 
 let &cpo = s:save_cpo