v/vlib/builtin/array_shrinkage_test.v

fn show_array(name string, a []int) {
	eprintln('${name:10} .flags: ${a.flags:34} | .cap: ${a.cap:2} | .len: ${a.len:2} | .data: $a.data | $a')
}

fn trace_delete_elements(name string, mut a []int) int {
	a.delete_many(5, 3)
	show_array(name, a)
	a << 55
	show_array(name, a)
	a << 66
	show_array(name, a)
	a << 77
	res := a.cap
	eprintln('                                        <<   ${name:10} .cap: $a.cap >>')
	show_array(name, a)
	a << 88
	show_array(name, a)
	a << 99
	show_array(name, a)
	eprintln('-------------------------------')
	return res
}

fn test_array_cap_shrinkage_after_deletion() {
	mut a := [0]
	mut middle_cap := 0

	a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
	middle_cap = trace_delete_elements('normal', mut a)
	assert middle_cap == 14
	assert a.len == 12
	assert a.cap == 14

	a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
	unsafe { a.flags.set(.noslices) }
	middle_cap = dump(trace_delete_elements('noslices', mut a))
	assert middle_cap == 14
	assert a.len == 12
	assert a.cap == 14

	a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
	unsafe { a.flags.set(.noshrink) }
	middle_cap = dump(trace_delete_elements('noshrink', mut a))
	assert middle_cap == 14
	assert a.len == 12
	assert a.cap == 14

	// Note: when *both* flags are set, the memory block for the array
	// should NOT shrink on deleting array elements, thus << after the
	// deletion, will still have space (till .cap is reached).
	a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
	unsafe { a.flags.set(.noslices | .noshrink) }
	middle_cap = dump(trace_delete_elements('both', mut a))
	assert middle_cap == 10
	assert a.len == 12
	assert a.cap == 20
}