patch 8.2.0413: buffer menu does not handle special buffers properly

Problem:    Buffer menu does not handle special buffers properly.
Solution:   Keep a dictionary with buffer names to reliably keep track of
            entries.
            Also trigger BufFilePre and BufFilePost for command-line and
            terminal buffers when the name changes.
diff --git a/src/testdir/test_menu.vim b/src/testdir/test_menu.vim
index 5e7a77b..f8d8081 100644
--- a/src/testdir/test_menu.vim
+++ b/src/testdir/test_menu.vim
@@ -19,6 +19,41 @@
   call assert_equal('', v:errmsg)
 endfunc
 
+func Test_buffer_menu_special_buffers()
+  " Load in runtime menus
+  try
+    source $VIMRUNTIME/menu.vim
+  catch
+    call assert_report('error while loading menus: ' . v:exception)
+  endtry
+
+  let v:errmsg = ''
+  doautocmd LoadBufferMenu VimEnter
+  call assert_equal('', v:errmsg)
+
+  let orig_buffer_menus = execute("nmenu Buffers")
+
+  " Make a new command-line window, test that it does not create a new buffer
+  " menu.
+  call feedkeys("q::let cmdline_buffer_menus=execute('nmenu Buffers')\<CR>:q\<CR>", 'ntx')
+  call assert_equal(len(split(orig_buffer_menus, "\n")), len(split(cmdline_buffer_menus, "\n")))
+  call assert_equal(orig_buffer_menus, execute("nmenu Buffers"))
+
+  if has('terminal')
+    " Open a terminal window and test that it does not create a buffer menu
+    " item.
+    terminal
+    let term_buffer_menus = execute('nmenu Buffers')
+    call assert_equal(len(split(orig_buffer_menus, "\n")), len(split(term_buffer_menus, "\n")))
+    bwipe!
+    call assert_equal(orig_buffer_menus, execute("nmenu Buffers"))
+  endif
+
+  " Remove menus to clean up
+  source $VIMRUNTIME/delmenu.vim
+  call assert_equal('', v:errmsg)
+endfunc
+
 func Test_translate_menu()
   if !has('multi_lang')
     return
@@ -121,6 +156,7 @@
 " Test for menu item completion in command line
 func Test_menu_expand()
   " Create the menu itmes for test
+  menu Dummy.Nothing lll
   for i in range(1, 4)
     let m = 'menu Xmenu.A' .. i .. '.A' .. i
     for j in range(1, 4)
@@ -146,7 +182,7 @@
   " Test for <Up> to go up a menu
   call feedkeys(":emenu Xmenu.A\<Tab>\<Down>\<Up>\<Up>\<Up>" ..
         \ "\<C-A>\<C-B>\"\<CR>", 'xt')
-  call assert_equal('"emenu Buffers. Xmenu.', @:)
+  call assert_equal('"emenu Dummy. Xmenu.', @:)
 
   " Test for expanding only submenus
   call feedkeys(":popup Xmenu.\<C-A>\<C-B>\"\<CR>", 'xt')
@@ -166,6 +202,7 @@
 
   set wildmenu&
   unmenu Xmenu
+  unmenu Dummy
 
   " Test for expanding popup menus with some hidden items
   menu Xmenu.foo.A1 a1
@@ -175,7 +212,6 @@
   call feedkeys(":popup Xmenu.\<C-A>\<C-B>\"\<CR>", 'xt')
   call assert_equal('"popup Xmenu.foo', @:)
   unmenu Xmenu
-
 endfunc
 
 " Test for the menu_info() function