vim-patch:partial:8.1.0822: peeking and flushing output slows down execution

Problem:    Peeking and flushing output slows down execution.
Solution:   Do not update the mode message when global_busy is set.  Do not
            flush when only peeking for a character. (Ken Takata)
cb574f4154

Omit inchar() change: it breaks too many tests.

N/A patches for version.c:

vim-patch:8.2.5170: tiny issues

Problem:    Tiny issues.
Solution:   Tiny improvements.
944cc9ceba

src/nvim/edit.c

@@ -4251,7 +4251,7 @@ static bool ins_esc(long *count, int cmdchar, bool nomove)
   // Otherwise remove the mode message.
   if (reg_recording != 0 || restart_edit != NUL) {
     showmode();
-  } else if (p_smd) {
+  } else if (p_smd && !skip_showmode()) {
     msg("");
   }
   // Exit Insert mode

src/nvim/screen.c

@@ -5821,6 +5821,19 @@ void grid_del_lines(ScreenGrid *grid, int row, int line_count, int end, int col,
   }
 }
 
+/// @return true when postponing displaying the mode message: when not redrawing
+/// or inside a mapping.
+bool skip_showmode(void)
+{
+  // Call char_avail() only when we are going to show something, because it
+  // takes a bit of time.  redrawing() may also call char_avail().
+  if (global_busy || msg_silent != 0 || !redrawing() || (char_avail() && !KeyTyped)) {
+    redraw_cmdline = true;  // show mode later
+    return true;
+  }
+  return false;
+}
+
 // Show the current mode and ruler.
 //
 // If clear_cmdline is true, clear the rest of the cmdline.
@@ -5850,12 +5863,8 @@ int showmode(void)
                  || restart_edit != NUL
                  || VIsual_active));
   if (do_mode || reg_recording != 0) {
-    // Don't show mode right now, when not redrawing or inside a mapping.
-    // Call char_avail() only when we are going to show something, because
-    // it takes a bit of time.
-    if (!redrawing() || (char_avail() && !KeyTyped) || msg_silent != 0) {
-      redraw_cmdline = true;                    // show mode later
-      return 0;
+    if (skip_showmode()) {
+      return 0;  // show mode later
     }
 
     bool nwr_save = need_wait_return;

test/functional/vimscript/null_spec.lua

@@ -135,7 +135,7 @@ describe('NULL', function()
     null_test('does not make Neovim crash when v:oldfiles gets assigned to that', ':let v:oldfiles = L|oldfiles', 0)
     null_expr_test('does not make complete() crash or error out',
                    'execute(":normal i\\<C-r>=complete(1, L)[-1]\\n")',
-                   '', '\n', function()
+                   0, '', function()
       eq({''}, curbufmeths.get_lines(0, -1, false))
     end)
     null_expr_test('is accepted by setmatches()', 'setmatches(L)', 0, 0)