From 37d97e771e9140746629bc3e67ad2dfbd39888c5 Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Mon, 12 Aug 2024 06:52:31 +0800
Subject: [PATCH] vim-patch:9.1.0672: marker folds may get corrupted on undo
 (#30026)

Problem:  marker folds may get corrupted on undo (Yousef Mohammed)
Solution: when adjusting folds, make sure that line1 is the lower limit
          and line2 is the upper line limit. In particular, line2 should
          not be able to get smaller than line1.

fixes: vim/vim#15455
closes: vim/vim#15466

https://github.com/vim/vim/commit/8d02e5cf961b06da5bc490ac5972bcbc252c4793

Co-authored-by: Christian Brabandt <cb@256bit.org>
---
 src/nvim/fold.c                |  6 ++++++
 test/old/testdir/test_fold.vim | 21 +++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/nvim/fold.c b/src/nvim/fold.c
index c8e6a25dbc..e7231c31ab 100644
--- a/src/nvim/fold.c
+++ b/src/nvim/fold.c
@@ -1336,6 +1336,9 @@ void deleteFoldRecurse(buf_T *bp, garray_T *gap)
 
 // foldMarkAdjust() {{{2
 /// Update line numbers of folds for inserted/deleted lines.
+///
+/// We are adjusting the folds in the range from line1 til line2,
+/// make sure that line2 does not get smaller than line1
 void foldMarkAdjust(win_T *wp, linenr_T line1, linenr_T line2, linenr_T amount,
                     linenr_T amount_after)
 {
@@ -1344,6 +1347,9 @@ void foldMarkAdjust(win_T *wp, linenr_T line1, linenr_T line2, linenr_T amount,
   if (amount == MAXLNUM && line2 >= line1 && line2 - line1 >= -amount_after) {
     line2 = line1 - amount_after - 1;
   }
+  if (line2 < line1) {
+    line2 = line1;
+  }
   // If appending a line in Insert mode, it should be included in the fold
   // just above the line.
   if ((State & MODE_INSERT) && amount == 1 && line2 == MAXLNUM) {
diff --git a/test/old/testdir/test_fold.vim b/test/old/testdir/test_fold.vim
index a0eb3afdbb..6569e032f6 100644
--- a/test/old/testdir/test_fold.vim
+++ b/test/old/testdir/test_fold.vim
@@ -1756,4 +1756,25 @@ func Test_cursor_down_fold_eob()
   bwipe!
 endfunc
 
+" issue: #15455
+func Test_cursor_fold_marker_undo()
+  new
+  call setline(1, ['{{{', '', 'This is a Line', '', 'This is a Line', '', '}}}'])
+  let &ul=&ul
+  setl foldmethod=marker
+  call cursor(2, 1)
+  norm! zo1vjdu
+  call assert_equal(1, foldlevel('.'))
+  bwipe!
+  new
+  call setline(1, ['', '{{{', '', 'This is a Line', '', 'This is a Line', '', '}}}'])
+  let &ul=&ul
+  setl foldmethod=marker
+  call cursor(3, 1)
+  norm! zo
+  norm! vjdu
+  call assert_equal(1, foldlevel('.'))
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab