Bottom up mode for custom menu (#848)

* Try to fix col adjustment (#843)

* Try to fix col adjuastment

* Improve duplicated text handling

* Bottom up mode for custom entry menu

When in command line mode, the custom entry window opens up to an
unexpected height, depending on the current count of completion items.
The above makes it hard to anticipate where to look at, and makes life a bit
harder.

This patch adds an option to open the custom entries view in a bottom up
mode, and flips the regular behaviour of next/prev entry in this mode.
Setup is as easy as:

```
cmp.setup.cmdline(':', {
  view = {
    entries = {name = 'custom', direction = 'bottom_up' }
  }
}
```

* fix stylua complaints

* sylua barfs

* solve some corner cases

* properly reverse entries table

* make custom view follow cursor

* respect default as top_down

* stylua

* more stylua

Co-authored-by: hrsh7th <hrsh7th@gmail.com>

lua/cmp/view/custom_entries_view.lua

@@ -43,6 +43,7 @@ custom_entries_view.new = function()
   self.offset = -1
   self.active = false
   self.entries = {}
+  self.bottom_up = false
 
   autocmd.subscribe(
     'CompleteChanged',
@@ -105,6 +106,17 @@ custom_entries_view.on_change = function(self)
   self.active = false
 end
 
+custom_entries_view.is_direction_top_down = function(self)
+  local c = config.get()
+  if (c.view and c.view.entries and c.view.entries.selection_order) == 'top_down' then
+    return true
+  elseif c.view.entries == nil or c.view.entries.selection_order == nil then
+    return true
+  else
+    return not self.bottom_up
+  end
+end
+
 custom_entries_view.open = function(self, offset, entries)
   self.offset = offset
   self.entries = {}
@@ -117,7 +129,6 @@ custom_entries_view.open = function(self, offset, entries)
   local lines = {}
   local dedup = {}
   local preselect = 0
-  local i = 1
   for _, e in ipairs(entries) do
     local view = e:get_view(offset, entries_buf)
     if view.dup == 1 or not dedup[e.completion_item.label] then
@@ -128,9 +139,8 @@ custom_entries_view.open = function(self, offset, entries)
       table.insert(self.entries, e)
       table.insert(lines, ' ')
       if preselect == 0 and e.completion_item.preselect then
-        preselect = i
+        preselect = #self.entries
       end
-      i = i + 1
     end
   end
   vim.api.nvim_buf_set_lines(entries_buf, 0, -1, false, lines)
@@ -161,6 +171,22 @@ custom_entries_view.open = function(self, offset, entries)
     col = vim.o.columns - width - 1
   end
 
+  if pos[1] > row then
+    self.bottom_up = true
+  else
+    self.bottom_up = false
+  end
+
+  if not self:is_direction_top_down() then
+    local n = #self.entries
+    for i = 1, math.floor(n / 2) do
+      self.entries[i], self.entries[n - i + 1] = self.entries[n - i + 1], self.entries[i]
+    end
+    if preselect ~= 0 then
+      preselect = #self.entries - preselect + 1
+    end
+  end
+
   self.entries_win:open({
     relative = 'editor',
     style = 'minimal',
@@ -170,12 +196,22 @@ custom_entries_view.open = function(self, offset, entries)
     height = height,
     zindex = 1001,
   })
+  -- always set cursor when starting. It will be adjusted on the call to _select
+  vim.api.nvim_win_set_cursor(self.entries_win.win, { 1, 0 })
   if preselect > 0 and config.get().preselect == types.cmp.PreselectMode.Item then
     self:_select(preselect, { behavior = types.cmp.SelectBehavior.Select })
   elseif not string.match(config.get().completion.completeopt, 'noselect') then
-    self:_select(1, { behavior = types.cmp.SelectBehavior.Select })
+    if self:is_direction_top_down() then
+      self:_select(1, { behavior = types.cmp.SelectBehavior.Select })
+    else
+      self:_select(#self.entries - 1, { behavior = types.cmp.SelectBehavior.Select })
+    end
   else
-    self:_select(0, { behavior = types.cmp.SelectBehavior.Select })
+    if self:is_direction_top_down() then
+      self:_select(0, { behavior = types.cmp.SelectBehavior.Select })
+    else
+      self:_select(#self.entries + 1, { behavior = types.cmp.SelectBehavior.Select })
+    end
   end
 end
 
@@ -185,6 +221,7 @@ custom_entries_view.close = function(self)
   self.active = false
   self.entries = {}
   self.entries_win:close()
+  self.bottom_up = false
 end
 
 custom_entries_view.abort = function(self)
@@ -237,11 +274,16 @@ end
 
 custom_entries_view.select_next_item = function(self, option)
   if self:visible() then
-    local cursor = vim.api.nvim_win_get_cursor(self.entries_win.win)[1] + 1
+    local cursor = vim.api.nvim_win_get_cursor(self.entries_win.win)[1]
+    if self:is_direction_top_down() then
+      cursor = cursor + 1
+    else
+      cursor = cursor - 1
+    end
     if not self.entries_win:option('cursorline') then
-      cursor = 1
+      cursor = (self:is_direction_top_down() and 1) or #self.entries
     elseif #self.entries < cursor then
-      cursor = 0
+      cursor = (not self:is_direction_top_down() and #self.entries + 1) or 0
     end
     self:_select(cursor, option)
   end
@@ -249,9 +291,16 @@ end
 
 custom_entries_view.select_prev_item = function(self, option)
   if self:visible() then
-    local cursor = vim.api.nvim_win_get_cursor(self.entries_win.win)[1] - 1
+    local cursor = vim.api.nvim_win_get_cursor(self.entries_win.win)[1]
+    if self:is_direction_top_down() then
+      cursor = cursor - 1
+    else
+      cursor = cursor + 1
+    end
     if not self.entries_win:option('cursorline') then
-      cursor = #self.entries
+      cursor = (self:is_direction_top_down() and #self.entries) or 1
+    elseif #self.entries < cursor then
+      cursor = (not self:is_direction_top_down() and 0) or #self.entries + 1
     end
     self:_select(cursor, option)
   end
@@ -273,7 +322,7 @@ end
 
 custom_entries_view.get_first_entry = function(self)
   if self:visible() then
-    return self.entries[1]
+    return (self:is_direction_top_down() and self.entries[1]) or self.entries[#self.entries]
   end
 end
 
@@ -295,9 +344,13 @@ custom_entries_view._select = function(self, cursor, option)
     self.prefix = string.sub(api.get_current_line(), self.offset, api.get_cursor()[2]) or ''
   end
 
-  self.active = cursor > 0 and is_insert
-  self.entries_win:option('cursorline', cursor > 0)
-  vim.api.nvim_win_set_cursor(self.entries_win.win, { math.max(cursor, 1), 0 })
+  self.active = cursor > 0 and cursor <= #self.entries and is_insert
+  self.entries_win:option('cursorline', cursor > 0 and cursor <= #self.entries)
+
+  vim.api.nvim_win_set_cursor(self.entries_win.win, {
+    math.max(math.min(cursor, #self.entries), 1),
+    0,
+  })
 
   if is_insert then
     self:_insert(self.entries[cursor] and self.entries[cursor]:get_vim_item(self.offset).word or self.prefix)