From ccfde4d028e891a41e3548323c3d47b06fb0b83e Mon Sep 17 00:00:00 2001
From: Bram Moolenaar <Bram@vim.org>
Date: Mon, 5 Sep 2022 19:51:13 +0100
Subject: [PATCH] patch 9.0.0389: crash when 'tagfunc' closes the window

Problem:    Crash when 'tagfunc' closes the window.
Solution:   Bail out when the window was closed.

---
 src/errors.h                 |  2 ++
 src/tag.c                    | 10 ++++++++++
 src/testdir/test_tagfunc.vim | 12 ++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/src/errors.h b/src/errors.h
index 43a1c9b..bfb4ae8 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3304,3 +3304,5 @@ EXTERN char e_could_not_check_for_pending_sigalrm_str[]
 EXTERN char e_substitute_nesting_too_deep[]
 	INIT(= N_("E1290: substitute nesting too deep"));
 #endif
+EXTERN char e_window_unexpectedly_close_while_searching_for_tags[]
+	INIT(= N_("E1299: Window unexpectedly closed while searching for tags"));
diff --git a/src/tag.c b/src/tag.c
index 8edb0c7..b4915cb 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -690,6 +690,16 @@ do_tag(
 		max_num_matches = MAXCOL; // If less than max_num_matches
 					  // found: all matches found.
 
+		// A tag function may do anything, which may cause various
+	    // information to become invalid.  At least check for the tagstack
+	    // to still be the same.
+	    if (tagstack != curwin->w_tagstack)
+	    {
+		emsg(_(e_window_unexpectedly_close_while_searching_for_tags));
+		FreeWild(new_num_matches, new_matches);
+		break;
+	    }
+
 	    // If there already were some matches for the same name, move them
 	    // to the start.  Avoids that the order changes when using
 	    // ":tnext" and jumping to another file.
diff --git a/src/testdir/test_tagfunc.vim b/src/testdir/test_tagfunc.vim
index 9582612..c10a82d 100644
--- a/src/testdir/test_tagfunc.vim
+++ b/src/testdir/test_tagfunc.vim
@@ -401,4 +401,16 @@ func Test_tagfunc_wipes_buffer()
   set tagfunc=
 endfunc
 
+func Test_tagfunc_closes_window()
+  split any
+  func MytagfuncClose(pat, flags, info)
+    close
+    return [{'name' : 'mytag', 'filename' : 'Xtest', 'cmd' : '1'}]
+  endfunc
+  set tagfunc=MytagfuncClose
+  call assert_fails('tag xyz', 'E1299:')
+
+  set tagfunc=
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
-- 
2.33.0