vim-patch:8.1.0397: no event triggered after updating diffs

Problem:    No event triggered after updating diffs.
Solution:   Add the DiffUpdated event.

e8fa05b5bc

runtime/doc/autocmd.txt

@@ -628,6 +628,11 @@ CursorMoved			After the cursor was moved in Normal or Visual
 CursorMovedI			After the cursor was moved in Insert mode.
 				Not triggered when the popup menu is visible.
 				Otherwise the same as CursorMoved.
+							*DiffUpdated*
+DiffUpdated			After diffs have been updated.  Depending on
+				what kind of diff is being used (internal or
+				external) this can be triggered on every
+				change or when doing |:diffupdate|.
 							*DirChanged*
 DirChanged			After the |current-directory| was changed.
 				Sets these |v:event| keys:

src/nvim/auevents.lua

@@ -33,6 +33,7 @@ return {
     'CursorHoldI',            -- idem, in Insert mode
     'CursorMoved',            -- cursor was moved
     'CursorMovedI',           -- cursor was moved in Insert mode
+    'DiffUpdated',            -- diffs have been updated
     'DirChanged',             -- directory changed
     'EncodingChanged',        -- after changing the 'encoding' option
     'ExitPre',                -- before exiting

src/nvim/diff.c

@@ -924,6 +924,8 @@ void ex_diffupdate(exarg_T *eap)
   curwin->w_valid_cursor.lnum = 0;
 
   diff_redraw(true);
+
+  apply_autocmds(EVENT_DIFFUPDATED, NULL, NULL, false, curbuf);
 }
 
 ///

src/nvim/testdir/test_diffmode.vim

@@ -2,6 +2,9 @@
 
 func Test_diff_fold_sync()
   enew!
+  let g:update_count = 0
+  au DiffUpdated * let g:update_count += 1
+
   let l = range(50)
   call setline(1, l)
   diffthis
@@ -27,6 +30,9 @@ func Test_diff_fold_sync()
   call win_gotoid(winone)
   call assert_equal(23, getcurpos()[1])
 
+  call assert_equal(1, g:update_count)
+  au! DiffUpdated
+
   windo diffoff
   close!
   set nomodified