# HG changeset patch
# User Bram Moolenaar <Bram@vim.org>
# Date 1634230807 -7200
# Node ID 560132056b97e92edf5ad9fb8aaa453457ce3743
# Parent  8b36e7633cee03a1eff93645d37948e149ff8f16
patch 8.2.3509: undo file is not synced

Commit: https://github.com/vim/vim/commit/340dd0fbe462a15a9678cfba02085b4adcc45f02
Author: Bram Moolenaar <Bram@vim.org>
Date:   Thu Oct 14 17:52:23 2021 +0100

    patch 8.2.3509: undo file is not synced

    Problem:    Undo file is not synced. (Sami Farin)
    Solution:   Sync the undo file if 'fsync' is set. (Christian Brabandt,
                closes #8879, closes #8920)

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3610,8 +3610,8 @@ A jump table for the options with a shor
 	systems without an fsync() implementation, this variable is always
 	off.
 	Also see 'swapsync' for controlling fsync() on swap files.
-	'fsync' also applies to |writefile()|, unless a flag is used to
-	overrule it.
+	'fsync' also applies to |writefile()| (unless a flag is used to
+	overrule it) and when writing undo files (see |undo-persistence|).
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
 
diff --git a/src/undo.c b/src/undo.c
--- a/src/undo.c
+++ b/src/undo.c
@@ -1786,6 +1786,11 @@ u_write_undo(
 	write_ok = FALSE;
 #endif
 
+#if defined(UNIX) && defined(HAVE_FSYNC)
+    if (p_fs && fflush(fp) == 0 && vim_fsync(fd) != 0)
+	write_ok = FALSE;
+#endif
+
 write_error:
     fclose(fp);
     if (!write_ok)
diff --git a/src/version.c b/src/version.c
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3509,
+/**/
     3508,
 /**/
     3507,