patch 9.0.0246: using freed memory when 'tagfunc' deletes the buffer

Problem:    Using freed memory when 'tagfunc' deletes the buffer.
Solution:   Make a copy of the tag name.

src/tag.c

@@ -281,6 +281,7 @@ do_tag(
     char_u	*buf_ffname = curbuf->b_ffname;	    // name to use for
 						    // priority computation
     int		use_tfu = 1;
+    char_u	*tofree = NULL;
 
     // remember the matches for the last used tag
     static int		num_matches = 0;
@@ -630,7 +631,12 @@ do_tag(
 	 * When desired match not found yet, try to find it (and others).
 	 */
 	if (use_tagstack)
-	    name = tagstack[tagstackidx].tagname;
+	{
+	    // make a copy, the tagstack may change in 'tagfunc'
+	    name = vim_strsave(tagstack[tagstackidx].tagname);
+	    vim_free(tofree);
+	    tofree = name;
+	}
 #if defined(FEAT_QUICKFIX)
 	else if (g_do_tagpreview != 0)
 	    name = ptag_entry.tagname;
@@ -922,6 +928,7 @@ do_tag(
     g_do_tagpreview = 0;	// don't do tag preview next time
 # endif
 
+    vim_free(tofree);
 #ifdef FEAT_CSCOPE
     return jumped_to_tag;
 #else

src/testdir/test_tagfunc.vim

@@ -389,4 +389,16 @@ func Test_tagfunc_callback()
   %bw!
 endfunc
 
+func Test_tagfunc_wipes_buffer()
+  func g:Tag0unc0(t,f,o)
+   bwipe
+  endfunc
+  set tagfunc=g:Tag0unc0
+  new
+  cal assert_fails('tag 0', 'E987:')
+
+  delfunc g:Tag0unc0
+  set tagfunc=
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -731,6 +731,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    246,
 /**/
     245,
 /**/