1// Copyright 2018 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// This test makes sure that t.s = t.s[0:x] doesn't write
6// either the slice pointer or the capacity.
7// See issue #14855.
8
9package main
10
11import "testing"
12
13const N = 1000000
14
15type X struct {
16	s []int
17}
18
19func TestSlice(t *testing.T) {
20	done := make(chan struct{})
21	a := make([]int, N+10)
22
23	x := &X{a}
24
25	go func() {
26		for i := 0; i < N; i++ {
27			x.s = x.s[1:9]
28		}
29		done <- struct{}{}
30	}()
31	go func() {
32		for i := 0; i < N; i++ {
33			x.s = x.s[0:8] // should only write len
34		}
35		done <- struct{}{}
36	}()
37	<-done
38	<-done
39
40	if cap(x.s) != cap(a)-N {
41		t.Errorf("wanted cap=%d, got %d\n", cap(a)-N, cap(x.s))
42	}
43	if &x.s[0] != &a[N] {
44		t.Errorf("wanted ptr=%p, got %p\n", &a[N], &x.s[0])
45	}
46}
47