feat: add option for view to follow cursor (#1727)

* feat: add option for custom entry view to follow cursor

Creates an option to allow the custom entries
view to follow the user's cursor as they type.

To enable, set
```lua
require("cmp").setup({
  view = {
    entries = {
      follow_cursor = true
    }
  }
})
```

Original source at 7569056388

Closes #1660

Co-authored-by: lvimuser <109605931+lvimuser@users.noreply.github.com>

* doc: add view.follow_cursor option to docs

---------

Co-authored-by: lvimuser <109605931+lvimuser@users.noreply.github.com>

doc/cmp.txt

@@ -686,6 +686,13 @@ view.docs.auto_open~
 
   Specify whether to show the docs_view when selecting an item.
 
+                                                 *cmp-config.view.follow_cursor*
+view.follow_cursor*
+  `boolean`
+
+  Specify whether the pmenu should follow the current position of the cursor
+  as the user types. `false` by default.
+
                            *cmp-config.window.{completion,documentation}.border*
 window.{completion,documentation}.border~
   `string | string[] | nil`

lua/cmp/config/default.lua

@@ -97,6 +97,7 @@ return function()
       entries = {
         name = 'custom',
         selection_order = 'top_down',
+        follow_cursor = false,
       },
       docs = {
         auto_open = true,

lua/cmp/types/cmp.lua

@@ -184,6 +184,7 @@ cmp.ItemField = {
 ---@class cmp.CustomEntriesViewConfig
 ---@field name 'custom'
 ---@field selection_order 'top_down'|'near_cursor'
+---@field follow_cursor boolean
 
 ---@class cmp.NativeEntriesViewConfig
 ---@field name 'native'

lua/cmp/view/custom_entries_view.lua

@@ -161,9 +161,12 @@ custom_entries_view.open = function(self, offset, entries)
   height = height ~= 0 and height or #self.entries
   height = math.min(height, #self.entries)
 
+  local delta = 0
+  if not config.get().view.entries.follow_cursor then
+    local cursor_before_line = api.get_cursor_before_line()
+    delta = vim.fn.strdisplaywidth(cursor_before_line:sub(self.offset))
+  end
   local pos = api.get_screen_cursor()
-  local cursor_before_line = api.get_cursor_before_line()
-  local delta = vim.fn.strdisplaywidth(cursor_before_line:sub(self.offset))
   local row, col = pos[1], pos[2] - delta - 1
 
   local border_info = window.get_border_info({ style = completion })