From f0d3d4a42657dca996e790aa829de3c6be7fdb63 Mon Sep 17 00:00:00 2001
From: Christian Brabandt <cb@256bit.org>
Date: Thu, 15 Feb 2024 20:15:04 +0100
Subject: [PATCH] patch 9.1.0112: Remove undo information, when cleaning
 quickfix buffer

Problem:  When the quickfix buffer has been modified an autocommand
          may invalidate the undo stack (kawarimidoll)
Solution: When clearing the quickfix buffer, also wipe the undo stack

fixes: #13905
closes: #13928

Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/quickfix.c               | 10 ++++++++++
 src/testdir/test_autocmd.vim | 28 ++++++++++++++++++++++++++++
 src/version.c                |  2 ++
 3 files changed, 40 insertions(+)

diff --git a/src/quickfix.c b/src/quickfix.c
index dd681ca23..3e2d3dfcc 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -4829,8 +4829,18 @@ qf_fill_buffer(qf_list_T *qfl, buf_T *buf, qfline_T *old_last, int qf_winid)
 	}
 
 	// delete all existing lines
+	//
+	// Note: we cannot store undo information, because
+	// qf buffer is usually not allowed to be modified.
+	//
+	// So we need to clean up undo information
+	// otherwise autocommands may invalidate the undo stack
 	while ((curbuf->b_ml.ml_flags & ML_EMPTY) == 0)
 	    (void)ml_delete((linenr_T)1);
+
+	// Remove all undo information
+	u_blockfree(curbuf);
+	u_clearall(curbuf);
     }
 
     // Check if there is anything to display
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 6e1223275..90dc3c1d3 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -4413,4 +4413,32 @@ func Test_autocmd_shortmess()
   delfunc SetupVimTest_shm
 endfunc
 
+func Test_autocmd_invalidates_undo_on_textchanged()
+  CheckRunVimInTerminal
+  let script =<< trim END
+    set hidden
+    " create quickfix list (at least 2 lines to move line)
+    vimgrep /u/j %
+
+    " enter quickfix window
+    cwindow
+
+    " set modifiable
+    setlocal modifiable
+
+    " set autocmd to clear quickfix list
+
+    autocmd! TextChanged <buffer> call setqflist([])
+    " move line
+    move+1
+  END
+  call writefile(script, 'XTest_autocmd_invalidates_undo_on_textchanged', 'D')
+  let buf = RunVimInTerminal('XTest_autocmd_invalidates_undo_on_textchanged', {'rows': 20})
+  call term_sendkeys(buf, ":so %\<cr>")
+  call term_sendkeys(buf, "G")
+  call WaitForAssert({-> assert_match('^XTest_autocmd_invalidates_undo_on_textchanged\s*$', term_getline(buf, 20))}, 1000)
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 72495c2f9..d23c9ce5a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    112,
 /**/
     111,
 /**/