Commit: patch 9.1.1758: Diff mode crashes when adding text property in autocommand

[Christian Brabandt]

patch 9.1.1758: Diff mode crashes when adding text property in autocommand

Commit: https://github.com/vim/vim/commit/46e22fd2f73b03795a5922ba07621472713eddb3
Author: zeertzjq <zeer...@outlook.com>
Date: Sun Sep 14 11:01:26 2025 -0400

patch 9.1.1758: Diff mode crashes when adding text property in autocommand

Problem: Diff mode crashes when adding text property in autocommand
(after 9.1.1557).
Solution: Only restore ML_EMPTY memline flag, ignore the others
(zeertzjq).

fixes: #18288
closes: #18291

Signed-off-by: zeertzjq <zeer...@outlook.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/src/diff.c b/src/diff.c
index 1a60ee7ae..25b9ae977 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -917,7 +917,8 @@ diff_write(buf_T *buf, diffin_T *din, linenr_T start, linenr_T end)
cmdmod.cmod_flags = save_cmod_flags;
free_string_option(buf->b_p_ff);
buf->b_p_ff = save_ff;
- buf->b_ml.ml_flags = save_ml_flags;
+ buf->b_ml.ml_flags =
+ (buf->b_ml.ml_flags & ~ML_EMPTY) | (save_ml_flags & ML_EMPTY);
return r;
}

diff --git a/src/testdir/dumps/Test_diff_add_prop_in_autocmd_01.dump b/src/testdir/dumps/Test_diff_add_prop_in_autocmd_01.dump
new file mode 100644
index 000000000..88aa421c1
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_add_prop_in_autocmd_01.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1>f+0#0000000#ffff4012|o@1| @69
+| +0#0000e05#a8a8a8255@1|b+0#0000000#5fd7ff255|a|r| @69
+| +0#0000e05#a8a8a8255@1|b+0#0000000#5fd7ff255|a|z| @69
+|~+0#4040ff13#ffffff0| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|X+3#0000000&|d|i|f@1|s|p|l|i|t|_|f|i|l|e| @41|1|,|1| @11|A|l@1
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@72
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@72
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@72
+| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@72
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|[+1#0000000&|N|o| |N|a|m|e|]| @47|0|,|0|-|1| @9|A|l@1
+|"+0&&|X|d|i|f@1|s|p|l|i|t|_|f|i|l|e|"| |3|L|,| |1|2|B| @49
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index 42f9463b3..340397a27 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -3541,4 +3541,29 @@ func Test_diffget_diffput_diffanchors()
set diffanchors&
endfunc

+func Test_diff_add_prop_in_autocmd()
+ CheckScreendump
+
+ let lines =<< trim END
+ func MyDiff() abort
+ let f1 = readfile(v:fname_in)
+ let f2 = readfile(v:fname_new)
+ let f0 = diff(f1, f2)
+ call writefile(split(f0, "
"), v:fname_out)
+ endfunc
+
+ call prop_type_add('myprop', #{highlight: 'Search', override: 1})
+ autocmd OptionSet diff call prop_add(1, 1, #{type: 'myprop', length: 100})
+ set diffexpr=MyDiff()
+ END
+ call writefile(lines, 'Xtest_diff_add_prop_in_autocmd', 'D')
+ call writefile(['foo', 'bar', 'baz'], 'Xdiffsplit_file', 'D')
+
+ let buf = RunVimInTerminal('-S Xtest_diff_add_prop_in_autocmd', {})
+ call term_sendkeys(buf, ":diffsplit Xdiffsplit_file\<CR>")
+ call VerifyScreenDump(buf, 'Test_diff_add_prop_in_autocmd_01', {})
+
+ call StopVimInTerminal(buf)
+endfunc
+
" vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 51079ce76..e550f2f47 100644
--- a/src/version.c
+++ b/src/version.c
@@ -724,6 +724,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 1758,
/**/
1757,
/**/