patch 8.0.0670: can't use input() in a timer callback

Problem:    Can't use input() in a timer callback. (Cosmin Popescu)
Solution:   Reset vgetc_busy and set timer_busy. (Ozaki Kiichi, closes #1790,
            closes #1129)

src/evalfunc.c

@@ -3191,7 +3191,7 @@ f_feedkeys(typval_T *argvars, typval_T *rettv UNUSED)
 	    ins_typebuf(keys_esc, (remap ? REMAP_YES : REMAP_NONE),
 				  insert ? 0 : typebuf.tb_len, !typed, FALSE);
 	    vim_free(keys_esc);
-	    if (vgetc_busy)
+	    if (vgetc_busy || timer_busy)
 		typebuf_was_filled = TRUE;
 	    if (execute)
 	    {

src/ex_cmds2.c

@@ -1209,11 +1209,18 @@ check_due_timer(void)
 	this_due = GET_TIMEDIFF(timer, now);
 	if (this_due <= 1)
 	{
+	    int save_timer_busy = timer_busy;
+	    int save_vgetc_busy = vgetc_busy;
+
+	    timer_busy = timer_busy > 0 || vgetc_busy > 0;
+	    vgetc_busy = 0;
 	    timer->tr_firing = TRUE;
 	    timer_callback(timer);
 	    timer->tr_firing = FALSE;
 	    timer_next = timer->tr_next;
 	    did_one = TRUE;
+	    timer_busy = save_timer_busy;
+	    vgetc_busy = save_vgetc_busy;
 
 	    /* Only fire the timer again if it repeats and stop_timer() wasn't
 	     * called while inside the callback (tr_id == -1). */

src/globals.h

@@ -1659,6 +1659,7 @@ EXTERN int  in_free_unref_items INIT(= FALSE);
 
 #ifdef FEAT_TIMERS
 EXTERN int  did_add_timer INIT(= FALSE);
+EXTERN int  timer_busy INIT(= 0);   /* when timer is inside vgetc() then > 0 */
 #endif
 
 #ifdef FEAT_EVAL

src/testdir/test_timers.vim

@@ -172,5 +172,21 @@ func Test_stop_all_in_callback()
   call assert_equal(0, len(info))
 endfunc
 
+func FeedkeysCb(timer)
+  call feedkeys("hello\<CR>", 'nt')
+endfunc
+
+func InputCb(timer)
+  call timer_start(10, 'FeedkeysCb')
+  let g:val = input('?')
+  call Resume()
+endfunc
+
+func Test_input_in_timer()
+  let g:val = ''
+  call timer_start(10, 'InputCb')
+  call Standby(1000)
+  call assert_equal('hello', g:val)
+endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    670,
 /**/
     669,
 /**/