patch 8.0.1817: a timer may change v:count unexpectedly

Problem:    A timer may change v:count unexpectedly.
Solution:   Save and restore v:count and similar variables when a timer
            callback is invoked. (closes #2897)

src/eval.c

@@ -6461,6 +6461,29 @@ set_vcount(
    vimvars[VV_COUNT1].vv_nr = count1;
}

/*
 * Save variables that might be changed as a side effect.  Used when executing
 * a timer callback.
 */
    void
save_vimvars(vimvars_save_T *vvsave)
{
    vvsave->vv_prevcount = vimvars[VV_PREVCOUNT].vv_nr;
    vvsave->vv_count = vimvars[VV_COUNT].vv_nr;
    vvsave->vv_count1 = vimvars[VV_COUNT1].vv_nr;
}

/*
 * Restore variables saved by save_vimvars().
 */
    void
restore_vimvars(vimvars_save_T *vvsave)
{
    vimvars[VV_PREVCOUNT].vv_nr = vvsave->vv_prevcount;
    vimvars[VV_COUNT].vv_nr = vvsave->vv_count;
    vimvars[VV_COUNT1].vv_nr = vvsave->vv_count1;
}

/*
 * Set string v: variable to a copy of "val".
 */

src/ex_cmds2.c

@@ -1336,6 +1336,8 @@ check_due_timer(void)
	this_due = proftime_time_left(&timer->tr_due, &now);
	if (this_due <= 1)
	{
	    /* Save and restore a lot of flags, because the timer fires while
	     * waiting for a character, which might be halfway a command. */
	    int save_timer_busy = timer_busy;
	    int save_vgetc_busy = vgetc_busy;
	    int save_did_emsg = did_emsg;
@@ -1345,6 +1347,7 @@ check_due_timer(void)
	    int save_did_throw = did_throw;
	    int save_ex_pressedreturn = get_pressedreturn();
	    except_T *save_current_exception = current_exception;
	    vimvars_save_T vvsave;

	    /* Create a scope for running the timer callback, ignoring most of
	     * the current scope, such as being inside a try/catch. */
@@ -1357,6 +1360,7 @@ check_due_timer(void)
	    trylevel = 0;
	    did_throw = FALSE;
	    current_exception = NULL;
	    save_vimvars(&vvsave);

	    timer->tr_firing = TRUE;
	    timer_callback(timer);
@@ -1373,6 +1377,7 @@ check_due_timer(void)
	    trylevel = save_trylevel;
	    did_throw = save_did_throw;
	    current_exception = save_current_exception;
	    restore_vimvars(&vvsave);
	    if (must_redraw != 0)
		need_update_screen = TRUE;
	    must_redraw = must_redraw > save_must_redraw

src/proto/eval.pro

@@ -67,6 +67,8 @@ list_T *get_vim_var_list(int idx);
dict_T *get_vim_var_dict(int idx);
void set_vim_var_char(int c);
void set_vcount(long count, long count1, int set_prevcount);
void save_vimvars(vimvars_save_T *vvsave);
void restore_vimvars(vimvars_save_T *vvsave);
void set_vim_var_string(int idx, char_u *val, int len);
void set_vim_var_list(int idx, list_T *val);
void set_vim_var_dict(int idx, dict_T *val);

src/structs.h

@@ -3423,3 +3423,9 @@ typedef struct {
    int		save_opcount;
    tasave_T	tabuf;
} save_state_T;

typedef struct {
    varnumber_T vv_prevcount;
    varnumber_T vv_count;
    varnumber_T vv_count1;
} vimvars_save_T;

src/testdir/test_timers.vim

@@ -5,6 +5,7 @@ if !has('timers')
endif

source shared.vim
source screendump.vim

func MyHandler(timer)
  let g:val += 1
@@ -260,4 +261,35 @@ func Test_ex_mode()
  call timer_stop(timer)
endfunc

func Test_restore_count()
  if !CanRunVimInTerminal()
    return
  endif
  " Check that v:count is saved and restored, not changed by a timer.
  call writefile([
        \ 'nnoremap <expr><silent> L v:count ? v:count . "l" : "l"',
        \ 'func Doit(id)',
        \ '  normal 3j',
        \ 'endfunc',
        \ 'call timer_start(100, "Doit")',
	\ ], 'Xtrcscript')
  call writefile([
        \ '1-1234',
        \ '2-1234',
        \ '3-1234',
	\ ], 'Xtrctext')
  let buf = RunVimInTerminal('-S Xtrcscript Xtrctext', {})

  " Wait for the timer to move the cursor to the third line.
  call WaitForAssert({-> assert_equal(3, term_getcursor(buf)[0])})
  call assert_equal(1, term_getcursor(buf)[1])
  " Now check that v:count has not been set to 3
  call term_sendkeys(buf, 'L')
  call WaitForAssert({-> assert_equal(2, term_getcursor(buf)[1])})

  call StopVimInTerminal(buf)
  call delete('Xtrcscript')
  call delete('Xtrctext')
endfunc

" vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =

static int included_patches[] =
{   /* Add new patch number below this line */
/**/
    1817,
/**/
    1816,
/**/