fix(lsp): delete bufvar inside WinClosed event

Problem: floaing preview window can be closed by some
ex commands like `only` `fclose` which will not clean the bufvar

Solution: use WinClosed event with floating_winnr for clean
bufnr, and add test cases for vim.lsp.util.open_floating_preview

runtime/lua/vim/lsp/util.lua

@@ -1344,10 +1344,6 @@ local function close_preview_window(winnr, bufnrs)
 
     local augroup = 'preview_window_' .. winnr
     pcall(api.nvim_del_augroup_by_name, augroup)
-    local buf = vim.w[winnr].buf_hold_win
-    if buf and api.nvim_buf_is_valid(buf) then
-      vim.b[buf].lsp_floating_window = nil
-    end
     pcall(api.nvim_win_close, winnr, true)
   end)
 end
@@ -1613,7 +1609,6 @@ function M.open_floating_preview(contents, syntax, opts)
       { silent = true, noremap = true, nowait = true }
     )
     close_preview_autocmd(opts.close_events, floating_winnr, { floating_bufnr, bufnr })
-    vim.w[floating_winnr].buf_hold_win = bufnr
 
     -- save focus_id
     if opts.focus_id then
@@ -1622,6 +1617,22 @@ function M.open_floating_preview(contents, syntax, opts)
     api.nvim_buf_set_var(bufnr, 'lsp_floating_preview', floating_winnr)
   end
 
+  local augroup_name = ('closing_floating_preview_%d'):format(floating_winnr)
+  local ok =
+    pcall(api.nvim_get_autocmds, { group = augroup_name, pattern = tostring(floating_winnr) })
+  if not ok then
+    api.nvim_create_autocmd('WinClosed', {
+      group = api.nvim_create_augroup(augroup_name, {}),
+      pattern = tostring(floating_winnr),
+      callback = function()
+        if api.nvim_buf_is_valid(bufnr) then
+          vim.b[bufnr].lsp_floating_preview = nil
+        end
+        api.nvim_del_augroup_by_name(augroup_name)
+      end,
+    })
+  end
+
   if do_stylize then
     vim.wo[floating_winnr].conceallevel = 2
   end

test/functional/plugin/lsp/utils_spec.lua

@@ -5,6 +5,8 @@ local Screen = require('test.functional.ui.screen')
 local feed = n.feed
 local eq = t.eq
 local exec_lua = n.exec_lua
+local command, api = n.command, n.api
+local pcall_err = t.pcall_err
 
 describe('vim.lsp.util', function()
   before_each(n.clear)
@@ -265,6 +267,38 @@ describe('vim.lsp.util', function()
 
         eq(56, opts.height)
       end)
+
+      describe('vim.lsp.util.open_floating_preview', function()
+        local var_name = 'lsp_floating_preview'
+        local curbuf = api.nvim_get_current_buf()
+
+        it('clean bufvar after fclose', function()
+          exec_lua(function()
+            vim.lsp.util.open_floating_preview({ 'test' }, '', { height = 5, width = 2 })
+          end)
+          eq(true, api.nvim_win_is_valid(api.nvim_buf_get_var(curbuf, var_name)))
+          command('fclose')
+          eq(
+            'Key not found: lsp_floating_preview',
+            pcall_err(api.nvim_buf_get_var, curbuf, var_name)
+          )
+        end)
+
+        it('clean bufvar after CursorMoved', function()
+          local result = exec_lua(function()
+            vim.lsp.util.open_floating_preview({ 'test' }, '', { height = 5, width = 2 })
+            local winnr = vim.b[vim.api.nvim_get_current_buf()].lsp_floating_preview
+            local result = vim.api.nvim_win_is_valid(winnr)
+            vim.api.nvim_feedkeys(vim.keycode('G'), 'txn', false)
+            return result
+          end)
+          eq(true, result)
+          eq(
+            'Key not found: lsp_floating_preview',
+            pcall_err(api.nvim_buf_get_var, curbuf, var_name)
+          )
+        end)
+      end)
     end)
   end)
 end)