vim-patch:8.1.2044: no easy way to process postponed work

Problem:    No easy way to process postponed work. (Paul Jolly)
Solution:   Add the SafeState autocommand event.

8aeec40207

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/normal.c

@@ -482,6 +482,40 @@ bool check_text_or_curbuf_locked(oparg_T *oap)
   return true;
 }
 
+static bool was_safe = false;
+static int not_safe_now = 0;
+
+/// Trigger SafeState if currently in s safe state, that is "safe" is TRUE and
+/// there is no typeahead.
+void may_trigger_safestate(bool safe)
+{
+  bool is_safe = safe
+                 && stuff_empty()
+                 && typebuf.tb_len == 0
+                 && !global_busy;
+
+  if (is_safe) {
+    apply_autocmds(EVENT_SAFESTATE, NULL, NULL, false, curbuf);
+  }
+  was_safe = is_safe;
+}
+
+/// Entering a not-safe state.
+void enter_unsafe_state(void)
+{
+  not_safe_now++;
+}
+
+/// Leaving a not-safe state.  Trigger SafeState if we were in a safe state
+/// before first calling enter_not_safe_state().
+void leave_unsafe_state(void)
+{
+  not_safe_now--;
+  if (not_safe_now == 0 && was_safe) {
+    apply_autocmds(EVENT_SAFESTATE, NULL, NULL, false, curbuf);
+  }
+}
+
 /// Normal state entry point. This is called on:
 ///
 /// - Startup, In this case the function never returns.
@@ -1295,6 +1329,18 @@ static void normal_check_buffer_modified(NormalState *s)
   }
 }
 
+/// If nothing is pending and we are going to wait for the user to
+/// type a character, trigger SafeState.
+static void normal_check_safe_state(NormalState *s)
+{
+  may_trigger_safestate(!finish_op
+                        && s->oa.prev_opcount > 0
+                        && s->oa.prev_count0 == 0
+                        && s->oa.op_type == OP_NOP
+                        && s->oa.regname == NUL
+                        && restart_edit == 0);
+}
+
 static void normal_check_folds(NormalState *s)
 {
   // Include a closed fold completely in the Visual area.
@@ -1387,6 +1433,9 @@ static int normal_check(VimState *state)
   }
   quit_more = false;
 
+  // it's not safe unless normal_check_safe_state() is called
+  was_safe = false;
+
   // If skip redraw is set (for ":" in wait_return()), don't redraw now.
   // If there is nothing in the stuff_buffer or do_redraw is true,
   // update cursor and redraw.
@@ -1403,6 +1452,7 @@ static int normal_check(VimState *state)
     normal_check_text_changed(s);
     normal_check_window_scrolled(s);
     normal_check_buffer_modified(s);
+    normal_check_safe_state(s);
 
     // Updating diffs from changed() does not always work properly,
     // esp. updating folds.  Do an update just before redrawing if