nvim: modules: completion: Move key bindings in lua module

nvim-compe recently included instructions on using backspace and tab
correctly. Include the same configuration.

nvim/.config/nvim/after/plugin/compe.vim

@@ -1,16 +0,0 @@
-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>" :
-  \ compe#complete()
-
-inoremap <silent><expr> <CR>  compe#confirm('<CR>')
-inoremap <silent><expr> <C-e> compe#close('<C-e>')
-
-" Use <Tab> and <S-Tab> to navigate through popup menu
-inoremap <expr> <Tab>   pumvisible() ? "\<C-n>" : "\<Tab>"
-inoremap <expr> <S-Tab> pumvisible() ? "\<C-p>" : "\<S-Tab>"

nvim/.config/nvim/lua/modules/completion.lua

@@ -1,3 +1,5 @@
+local remap = vim.api.nvim_set_keymap
+
 require'compe'.setup {
   enabled              = true;
   autocomplete         = true;
@@ -22,3 +24,42 @@ require'compe'.setup {
     vsnip         = false;
   };
 }
+
+local t = function(str)
+  return vim.api.nvim_replace_termcodes(str, true, true, true)
+end
+
+local check_back_space = function()
+  local col = vim.fn.col('.') - 1
+  if col == 0 or vim.fn.getline('.'):sub(col, col):match('%s') then
+    return true
+  else
+    return false
+  end
+end
+
+-- Use (S-)tab to:
+-- Move to prev/next item in completion menuone
+
+_G.tab_complete = function()
+  if vim.fn.pumvisible() == 1 then
+    return t "<C-n>"
+  elseif check_back_space() then
+    return t "<Tab>"
+  else
+    return vim.fn['compe#complete']()
+  end
+end
+
+_G.s_tab_complete = function()
+  if vim.fn.pumvisible() == 1 then
+    return t "<C-p>"
+  else
+    return t "<S-Tab>"
+  end
+end
+
+remap("i", "<Tab>", "v:lua.tab_complete()", {expr = true})
+remap("s", "<Tab>", "v:lua.tab_complete()", {expr = true})
+remap("i", "<S-Tab>", "v:lua.s_tab_complete()", {expr = true})
+remap("s", "<S-Tab>", "v:lua.s_tab_complete()", {expr = true})