patch 9.1.1949: :stag does not use 'swichtbuf' option

Problem:  :stag does not use 'swichtbuf' option, though the
          documentation states differently
          (Christian Brabandt)
Solution: Respect 'switchbuf' option (Yegappan Lakshmanan).

related: #18845
closes: #18856

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/tag.c

@@ -3850,6 +3850,15 @@ jumpto_tag(
     if (getfile_result == GETFILE_UNUSED
 				  && (postponed_split || cmdmod.cmod_tab != 0))
     {
+	if (swb_flags & SWB_VSPLIT)
+	    // If 'switchbuf' contains 'vsplit', then use a new vertically
+	    // split window.
+	    cmdmod.cmod_split |= WSP_VERT;
+
+	if (swb_flags & SWB_NEWTAB)
+	    // If 'switchbuf' contains 'newtab', then use a new tabpage
+	    cmdmod.cmod_tab = tabpage_index(curtab) + 1;
+
 	if (win_split(postponed_split > 0 ? postponed_split : 0,
 						postponed_split_flags) == FAIL)
 	{

src/testdir/test_tagjump.vim

@@ -144,6 +144,24 @@ func Test_tagjump_switchbuf()
   1tabnext | stag third
   call assert_equal(2, tabpagenr('$'))
   call assert_equal(3, line('.'))
+  tabonly
+
+  " use a vertically split window
+  enew | only
+  set switchbuf=vsplit
+  stag third
+  call assert_equal(2, winnr('$'))
+  call assert_equal(1, winnr())
+  call assert_equal(3, line('.'))
+  call assert_equal(['row', [['leaf', win_getid(1)], ['leaf', win_getid(2)]]], winlayout())
+
+  " jump to a tag in a new tabpage
+  enew | only
+  set switchbuf=newtab
+  stag second
+  call assert_equal(2, tabpagenr('$'))
+  call assert_equal(2, tabpagenr())
+  call assert_equal(2, line('.'))
 
   tabclose!
   enew | only

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1949,
 /**/
     1948,
 /**/