Both of the below test cases work unless compiled against a debug runtime.

Test case 1:

void main() {
	int[] a = (cast(int*)null)[0..1];
	a.length = 1;
	assert (a.length == 1);
	assert (a[0] == 0);
}

Test case 2:

union Union {
	int i;
	ubyte[] a;
}
void main() {
	Union u;
	u.i = 10;
	u.a.length = 1;
	assert (u.a.length == 1);
	assert (u.a[0] == 1);
}

The problematic assertion is assert(!p.length || p.data). It occurs in three functions:

- _d_delarray
- _d_arraysetlengthT
- _d_arraysetlengthiT

The second one of the above is triggered by the given test cases. It'd be easy to come up with ones that trigger the other two as well.

This behaviour doesn't seem to be specified, so I'm not completely sure whether this should be fixed or not. I have two arguments in favour of removing the assertions:

1. They're only sanity checks: they don't actually matter for behaviour. Code which trips the asserts on a debug runtime runs fine on a release runtime. Nothing actually expects the assertions to succeed.

2. Code which relies on such behaviour actually exists: test case 2 was reduced from tango.text.Regex.

In Phobos, the functions are in phobos/internal/gc/gc.d; in Tango, they can be found in tango/lib/compiler/{dmd,gdc}/lifetime.d; in LDC, they're in runtime/internal/lifetime.d. This issue affects all of them.