vim-patch:8.2.1413: previous tab page not usable from an Ex command

Problem:    Previous tab page not usable from an Ex command.
Solution:   Add the "#" argument for :tabnext et al. (Yegappan Lakshmanan,
            closes vim/vim#6677)
94f4ffa770

Do not rename old_curtab to prev_tp in win_new_tabpage, this can be confused
with the previous tabpage (`:tabprevious`).

Cherry-pick ex_errmsg from v8.2.1280.
8930caaa1a

src/nvim/ex_docmd.c

@@ -2036,6 +2036,18 @@ doend:
   return ea.nextcmd;
 }
 
+static char ex_error_buf[MSG_BUF_LEN];
+
+/// @return an error message with argument included.
+/// Uses a static buffer, only the last error will be kept.
+/// "msg" will be translated, caller should use N_().
+char *ex_errmsg(const char *const msg, const char_u *const arg)
+  FUNC_ATTR_NONNULL_ALL
+{
+  vim_snprintf(ex_error_buf, MSG_BUF_LEN, _(msg), arg);
+  return ex_error_buf;
+}
+
 // Parse and skip over command modifiers:
 // - update eap->cmd
 // - store flags in "cmdmod".
@@ -4861,7 +4873,13 @@ static int get_tabpage_arg(exarg_T *eap)
       if (STRCMP(p, "$") == 0) {
         tab_number = LAST_TAB_NR;
       } else if (STRCMP(p, "#") == 0) {
+        if (valid_tabpage(lastused_tabpage)) {
           tab_number = tabpage_index(lastused_tabpage);
+        } else {
+          eap->errmsg = ex_errmsg(e_invargval, eap->arg);
+          tab_number = 0;
+          goto theend;
+        }
       } else if (p == p_save || *p_save == '-' || *p != NUL
                  || tab_number > LAST_TAB_NR) {
         // No numbers as argument.

src/nvim/testdir/test_tabpage.vim

@@ -692,6 +692,7 @@ func Test_lastused_tabpage()
   call assert_beeps('call feedkeys("g\<Tab>", "xt")')
   call assert_beeps('call feedkeys("\<C-Tab>", "xt")')
   call assert_beeps('call feedkeys("\<C-W>g\<Tab>", "xt")')
+  call assert_fails('tabnext #', 'E475:')
 
   " open four tab pages
   tabnew
@@ -716,17 +717,41 @@ func Test_lastused_tabpage()
   call assert_equal(4, tabpagenr())
   call assert_equal(2, tabpagenr('#'))
 
+  " Test for :tabnext #
+  tabnext #
+  call assert_equal(2, tabpagenr())
+  call assert_equal(4, tabpagenr('#'))
+
   " Try to jump to a closed tab page
-  tabclose 2
+  tabclose #
   call assert_equal(0, tabpagenr('#'))
   call feedkeys("g\<Tab>", "xt")
-  call assert_equal(3, tabpagenr())
+  call assert_equal(2, tabpagenr())
   call feedkeys("\<C-Tab>", "xt")
-  call assert_equal(3, tabpagenr())
+  call assert_equal(2, tabpagenr())
   call feedkeys("\<C-W>g\<Tab>", "xt")
-  call assert_equal(3, tabpagenr())
+  call assert_equal(2, tabpagenr())
+  call assert_fails('tabnext #', 'E475:')
+  call assert_equal(2, tabpagenr())
 
-  tabclose!
+  " Test for :tabonly #
+  let wnum = win_getid()
+  $tabnew
+  tabonly #
+  call assert_equal(wnum, win_getid())
+  call assert_equal(1, tabpagenr('$'))
+
+  " Test for :tabmove #
+  tabnew
+  let wnum = win_getid()
+  tabnew
+  tabnew
+  tabnext 2
+  tabmove #
+  call assert_equal(4, tabpagenr())
+  call assert_equal(wnum, win_getid())
+
+  tabonly!
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab