feat: separate highlight option for title of Borders (#260)

* wip: minimal setup for separate title highlights

* fix: out of bounds index when title is max size

* refactor: factor out `set_title_highlights`

* refactor: move check inside `set_title_highlights`

* fix: do refactor of `set_title_highlights` everywhere

Author: l-kershaw

lua/plenary/popup/init.lua

@@ -379,6 +379,8 @@ function popup.create(what, vim_options)
   local border = nil
   if should_show_border then
     border_options.focusable = vim_options.border_focusable
+    border_options.highlight = vim_options.borderhighlight and string.format("Normal:%s", vim_options.borderhighlight)
+    border_options.titlehighlight = vim_options.titlehighlight
     border = Border:new(bufnr, win_id, win_opts, border_options)
     popup._borders[win_id] = border
   end
@@ -387,10 +389,6 @@ function popup.create(what, vim_options)
     vim.api.nvim_win_set_option(win_id, "winhl", string.format("Normal:%s", vim_options.highlight))
   end
 
-  if should_show_border and vim_options.borderhighlight then
-    vim.api.nvim_win_set_option(border.win_id, "winhl", string.format("Normal:%s", vim_options.borderhighlight))
-  end
-
   -- enter
   local should_enter = vim_options.enter
   if should_enter == nil then

lua/plenary/window/border.lua

@@ -46,7 +46,13 @@ local create_horizontal_line = function(title, pos, width, left_char, mid_char,
     string.rep(mid_char, width - title_len - left_start),
     right_char
   )
-  return horizontal_line
+  local ranges
+  if title_len ~= 0 then
+    -- Need to calculate again due to multi-byte characters
+    local r_start = string.len(left_char) + math.max(left_start, 0) * string.len(mid_char)
+    ranges = { { r_start, r_start + string.len(title) } }
+  end
+  return horizontal_line, ranges
 end
 
 function Border._create_lines(content_win_options, border_win_options)
@@ -59,6 +65,7 @@ function Border._create_lines(content_win_options, border_win_options)
   local left_enabled = thickness.left == 1
 
   local border_lines = {}
+  local ranges = {}
 
   local topline = nil
 
@@ -85,14 +92,18 @@ function Border._create_lines(content_win_options, border_win_options)
   then
     for _, title in ipairs(titles) do
       if string.find(title.pos, "N") then
-        topline = create_horizontal_line(
+        local top_ranges
+        topline, top_ranges = create_horizontal_line(
           title.text,
           title.pos,
           content_win_options.width,
           topleft,
           border_win_options.top or "",
           topright
         )
+        for _, r in pairs(top_ranges) do
+          table.insert(ranges, { 0, r[1], r[2] })
+        end
         break
       end
     end
@@ -126,14 +137,18 @@ function Border._create_lines(content_win_options, border_win_options)
     local botright = (right_enabled and border_win_options.botright) or ""
     for _, title in ipairs(titles) do
       if string.find(title.pos, "S") then
-        botline = create_horizontal_line(
+        local bot_ranges
+        botline, bot_ranges = create_horizontal_line(
           title.text,
           title.pos,
           content_win_options.width,
           botleft,
           border_win_options.bot or "",
           botright
         )
+        for _, r in pairs(bot_ranges) do
+          table.insert(ranges, { content_win_options.height + 1, r[1], r[2] })
+        end
         break
       end
     end
@@ -145,7 +160,15 @@ function Border._create_lines(content_win_options, border_win_options)
     table.insert(border_lines, botline)
   end
 
-  return border_lines
+  return border_lines, ranges
+end
+
+local set_title_highlights = function(bufnr, ranges, hl)
+  if hl and ranges then
+    for _, r in pairs(ranges) do
+      vim.api.nvim_buf_add_highlight(bufnr, -1, hl, r[1], r[2], r[3])
+    end
+  end
 end
 
 function Border:change_title(new_title)
@@ -154,8 +177,10 @@ function Border:change_title(new_title)
   end
 
   self._border_win_options.title = new_title
-  self.contents = Border._create_lines(self.content_win_options, self._border_win_options)
+  self.contents, self.title_ranges = Border._create_lines(self.content_win_options, self._border_win_options)
   vim.api.nvim_buf_set_lines(self.bufnr, 0, -1, false, self.contents)
+
+  set_title_highlights(self.bufnr, self.title_ranges, self._border_win_options.titlehighlight)
 end
 
 -- Updates characters for border lines, and returns nvim_win_config
@@ -192,7 +217,8 @@ function Border:__align_calc_config(content_win_options, border_win_options)
   -- Ensure the relevant contests and border win_options are set
   self._border_win_options = border_win_options
   self.content_win_options = content_win_options
-  self.contents = Border._create_lines(content_win_options, border_win_options)
+  -- Update border characters and title_ranges
+  self.contents, self.title_ranges = Border._create_lines(content_win_options, border_win_options)
 
   vim.api.nvim_buf_set_lines(self.bufnr, 0, -1, false, self.contents)
 
@@ -225,6 +251,12 @@ function Border:new(content_bufnr, content_win_id, content_win_options, border_w
   local nvim_win_config = Border.__align_calc_config(obj, content_win_options, border_win_options)
   obj.win_id = vim.api.nvim_open_win(obj.bufnr, false, nvim_win_config)
 
+  if border_win_options.highlight then
+    vim.api.nvim_win_set_option(obj.win_id, "winhl", border_win_options.highlight)
+  end
+
+  set_title_highlights(obj.bufnr, obj.title_ranges, obj._border_win_options.titlehighlight)
+
   vim.cmd(
     string.format(
       "autocmd BufDelete <buffer=%s> ++nested ++once :lua require('plenary.window').close_related_win(%s, %s)",