feat: save/restore 'hlsearch' setting when opening/closing UI

As noted in comment, may add more settings later, but this is the one
that most annoys me, so starting with that.

Author: wincent

lua/wincent/commandt/private/includes.lua

@@ -0,0 +1,13 @@
+-- SPDX-FileCopyrightText: Copyright 2025-present Greg Hurrell and contributors.
+-- SPDX-License-Identifier: BSD-2-Clause
+
+local function includes(t, value)
+  for _, candidate in ipairs(t) do
+    if candidate == value then
+      return true
+    end
+  end
+  return false
+end
+
+return includes

lua/wincent/commandt/private/settings.lua

@@ -0,0 +1,42 @@
+-- SPDX-FileCopyrightText: Copyright 2025-present Greg Hurrell and contributors.
+-- SPDX-License-Identifier: BSD-2-Clause
+
+local includes = require('wincent.commandt.private.includes')
+
+local Settings = {}
+
+local settings = { 'hlsearch' }
+
+local mt = {
+  __index = Settings,
+  __newindex = function(t, key, value)
+    local saved = rawget(t, '_saved')
+    if includes(settings, key) then
+      if value == nil then
+        if saved[key] ~= nil then
+          -- Reset to previously saved value.
+          vim.opt[key] = saved[key]
+          saved[key] = nil
+        end
+      else
+        if saved[key] == nil then
+          -- Save current value.
+          saved[key] = vim.o[key]
+        end
+        vim.opt[key] = value
+      end
+    else
+      rawset(t, key, value)
+    end
+  end,
+}
+
+function Settings.new()
+  local m = {
+    _saved = {},
+  }
+  setmetatable(m, mt)
+  return m
+end
+
+return Settings

lua/wincent/commandt/private/ui.lua

@@ -5,6 +5,7 @@ local ui = {}
 
 local MatchListing = require('wincent.commandt.private.match_listing').MatchListing
 local Prompt = require('wincent.commandt.private.prompt').Prompt
+local Settings = require('wincent.commandt.private.settings')
 
 local candidate_count = nil
 local cmdline_enter_autocmd = nil
@@ -14,6 +15,7 @@ local match_listing = nil
 local prompt = nil
 local results = nil
 local selected = nil
+local settings = Settings.new()
 
 -- Reverses `list` in place.
 local reverse = function(list)
@@ -35,6 +37,9 @@ end
 -- do anything that would move you out)
 
 local close = function()
+  -- Restore global settings.
+  settings.hlsearch = nil
+
   if match_listing then
     match_listing:close()
     match_listing = nil
@@ -69,16 +74,17 @@ ui.open = function(kind)
   end
 end
 
--- TODO save/restore global options, like `hlsearch' (which we want to turn off
--- temporarily when our windows are visible) — either that, or figure out how to
--- make the highlighting not utterly suck.
--- in any case, review the list at ruby/command-t/lib/command-t/match_window.rb
 ui.show = function(finder, options)
   -- TODO validate options
   current_finder = finder
 
   current_window = vim.api.nvim_get_current_win()
 
+  -- Temporarily override global settings.
+  -- For now just 'hlsearch', but may add more later (see
+  -- ruby/command-t/lib/command-t/match_window.rb)
+  settings.hlsearch = false
+
   -- Work around an autocommand bug. We don't reliably get `WinClosed` events,
   -- or if we do, our call to `nvim_del_autocmd()` doesn't always clean up for
   -- us. So, we add some window-related autocommands to a group which we always