vim-patch:8.1.0394: diffs are not always updated correctly

Problem:    Diffs are not always updated correctly.
Solution:   When using internal diff update for any changes properly.

https://github.com/vim/vim/commit/e3521d9cbb786806eaff106707851d37d2c0ecef

4 files changed, 30 insertions, 8 deletions

diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index 238893260e..e8975f0622 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -842,6 +842,7 @@ struct tabpage_S {
   diff_T          *tp_first_diff;
   buf_T           *(tp_diffbuf[DB_COUNT]);
   int tp_diff_invalid;              ///< list of diffs is outdated
+  int tp_diff_update;               ///< update diffs before redrawing
   frame_T         *(tp_snapshot[SNAP_COUNT]);    ///< window layout snapshots
   ScopeDictDictItem tp_winvar;      ///< Variable for "t:" Dictionary.
   dict_T          *tp_vars;         ///< Internal variables, local to tab page.
diff --git a/src/nvim/diff.c b/src/nvim/diff.c
index 6e034485d9..a927983374 100644
--- a/src/nvim/diff.c
+++ b/src/nvim/diff.c
@@ -266,6 +266,15 @@ void diff_mark_adjust(linenr_T line1, linenr_T line2, long amount,
 static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1,
                                 linenr_T line2, long amount, long amount_after)
 {
+  if (diff_internal()) {
+    // Will udpate diffs before redrawing.  Set _invalid to update the
+    // diffs themselves, set _update to also update folds properly just
+    // before redrawing.
+    tp->tp_diff_invalid = true;
+    tp->tp_diff_update = true;
+    return;
+  }
+
   int inserted;
   int deleted;
   if (line2 == MAXLNUM) {
@@ -840,7 +849,7 @@ theend:
 /// Note that if the internal diff failed for one of the buffers, the external
 /// diff will be used anyway.
 ///
-static int diff_internal(void)
+int diff_internal(void)
 {
   return (diff_flags & DIFF_INTERNAL) != 0 && *p_dex == NUL;
 }
@@ -864,9 +873,9 @@ static int diff_internal_failed(void)
 
 /// Completely update the diffs for the buffers involved.
 ///
-/// This uses the ordinary "diff" command.
-/// The buffers are written to a file, also for unmodified buffers (the file
-/// could have been produced by autocommands, e.g. the netrw plugin).
+/// When using the external "diff" command the buffers are written to a file,
+/// also for unmodified buffers (the file could have been produced by
+/// autocommands, e.g. the netrw plugin).
 ///
 /// @param eap can be NULL
 void ex_diffupdate(exarg_T *eap)
diff --git a/src/nvim/misc1.c b/src/nvim/misc1.c
index d4a406cdba..d77c196a3a 100644
--- a/src/nvim/misc1.c
+++ b/src/nvim/misc1.c
@@ -1953,10 +1953,10 @@ changed_lines(
 {
   changed_lines_buf(curbuf, lnum, lnume, xtra);
 
-  if (xtra == 0 && curwin->w_p_diff) {
-    /* When the number of lines doesn't change then mark_adjust() isn't
-     * called and other diff buffers still need to be marked for
-     * displaying. */
+  if (xtra == 0 && curwin->w_p_diff && !diff_internal()) {
+    // When the number of lines doesn't change then mark_adjust() isn't
+    // called and other diff buffers still need to be marked for
+    // displaying.
     linenr_T wlnum;
 
     FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
@@ -2025,6 +2025,10 @@ static void changed_common(linenr_T lnum, colnr_T col, linenr_T lnume, long xtra
   /* mark the buffer as modified */
   changed();
 
+  if (curwin->w_p_diff && diff_internal()) {
+    curtab->tp_diff_update = true;
+  }
+
   /* set the '. mark */
   if (!cmdmod.keepjumps) {
     RESET_FMARK(&curbuf->b_last_change, ((pos_T) {lnum, col, 0}), 0);
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index f87de52a82..38ee0936aa 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -1325,6 +1325,14 @@ static int normal_check(VimState *state)
     normal_check_cursor_moved(s);
     normal_check_text_changed(s);
 
+    // Updating diffs from changed() does not always work properly,
+    // esp. updating folds.  Do an update just before redrawing if
+    // needed.
+    if (curtab->tp_diff_update || curtab->tp_diff_invalid) {
+      ex_diffupdate(NULL);
+      curtab->tp_diff_update = false;
+    }
+
     // Scroll-binding for diff mode may have been postponed until
     // here.  Avoids doing it for every change.
     if (diff_need_scrollbind) {