patch 9.1.1357: Vim incorrectly escapes tags with "[" in a help buffer

Problem:  Vim incorrectly escapes tags containing "[" in a help buffer
Solution: check if the buffer has the "help" filetype set, instead of
          already being a help buffer (Phạm Bình An)

fixes: #17224
closes: #17232

Co-authored-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Phạm Bình An <phambinhanctb2004@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/normal.c

@@ -3579,7 +3579,7 @@ nv_ident(cmdarg_T *cap)
 	    aux_ptr = (char_u *)(magic_isset() ? "/?.*~[^$\\" : "/?^$\\");
 	else if (tag_cmd)
 	{
-	    if (curbuf->b_help)
+	    if (STRCMP(curbuf->b_p_ft, "help") == 0)
 		// ":help" handles unescaped argument
 		aux_ptr = (char_u *)"";
 	    else

src/testdir/test_help.vim

@@ -205,5 +205,22 @@ func Test_help_using_visual_match()
   call v9.CheckScriptFailure(lines, 'E149:')
 endfunc
 
+func Test_helptag_navigation()
+  let helpdir = tempname()
+  let tempfile = helpdir . '/test.txt'
+  call mkdir(helpdir, 'pR')
+  call writefile(['', '*[tag*', '', '|[tag|'], tempfile)
+  exe 'helptags' helpdir
+  exe 'sp' tempfile
+  exe 'lcd' helpdir
+  setl ft=help
+  let &l:iskeyword='!-~,^*,^|,^",192-255'
+  call cursor(4, 2)
+  " Vim must not escape `[` when expanding the tag
+  exe "normal! \<C-]>"
+  call assert_equal(2, line('.'))
+  bw
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1357,
 /**/
     1356,
 /**/