fix whitespace highlighting

Before this fix, when cursor jump to another window, some char before
cursor in previous window would disappear, which probably is caused by
Conceal matches.

This fix removes cursor-related highlight matches when current window is
not focused.

lua/trim/highlighter.lua

@@ -13,30 +13,70 @@ local has_value = function(tbl, val)
   return false
 end
 
+function add_whitespace_matches()
+  if vim.w.trim_whitespace_match_ids == nil then
+    vim.w.trim_whitespace_match_ids = {
+      -- Trailing whitespaces
+      vim.fn.matchadd('ExtraWhitespace', '\\s\\+$'),
+      -- Trailing empty lines
+      vim.fn.matchadd('ExtraWhitespace', '^\\_s*\\%$'),
+    }
+  end
+end
+
+function add_cursor_matches()
+  if vim.w.trim_cursor_match_ids == nil then
+    vim.w.trim_cursor_match_ids = {
+      -- no highlight for whitespaces before cursor position
+      vim.fn.matchadd('Conceal', '\\s\\+\\%#'),
+      -- no highlight for lines before cursor line
+      vim.fn.matchadd('Conceal', '^\\_s*\\%#'),
+    }
+  end
+end
+
+function delete_whitespace_matches()
+  for _, matchid in ipairs(vim.w.trim_whitespace_match_ids or {}) do
+    vim.fn.matchdelete(matchid)
+  end
+  vim.w.trim_whitespace_match_ids = nil
+end
+
+function delete_cursor_matches()
+  for _, matchid in ipairs(vim.w.trim_cursor_match_ids or {}) do
+    vim.fn.matchdelete(matchid)
+  end
+  vim.w.trim_cursor_match_ids = nil
+end
+
 function highlighter.setup()
   vim.api.nvim_set_hl(0, 'ExtraWhitespace', {
     bg = config.highlight_bg,
     ctermbg = config.highlight_ctermbg,
   })
 
   local augroup = vim.api.nvim_create_augroup('TrimHighlight', { clear = true })
-  vim.api.nvim_create_autocmd('FileType', {
+  vim.api.nvim_create_autocmd({ 'BufEnter', 'WinEnter' }, {
     group = augroup,
-    pattern = '*',
     callback = function()
       if vim.bo.buftype == '' and not has_value(config.ft_blocklist, vim.bo.filetype) then
-        -- Trailing whitespaces
-        vim.fn.matchadd('ExtraWhitespace', '\\s\\+$')
-        -- no highlight for whitespaces before cursor position
-        vim.fn.matchadd('Conceal', '\\s\\+\\%#')
-
-        -- Trailing empty lines
-        vim.fn.matchadd('ExtraWhitespace', '^\\_s*\\%$')
-        -- no highlight for lines before cursor line
-        vim.fn.matchadd('Conceal', '^\\_s*\\%#')
+        add_whitespace_matches()
+        add_cursor_matches()
+      else
+        delete_whitespace_matches()
+        delete_cursor_matches()
       end
     end,
   })
+
+  -- After cursor left window, the matches related to cursor would not work,
+  -- so clear them on BufLeave/WinLeave
+  vim.api.nvim_create_autocmd({ 'BufLeave', 'WinLeave' }, {
+    group = augroup,
+    callback = function()
+      delete_cursor_matches()
+    end,
+  })
 end
 
 return highlighter