Array length extension ignores copy constructor

[dlangBugzillaToGithub]

Paul Backus (@pbackus) reported this on 2022-12-16T17:33:09Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=23563

Description

As of DMD 2.101.0, the following program compiles and runs successfully to completion:

---
struct S
{
    this(ref S)
    {
        assert(0);
    }
}

void main()
{
    S[] a = [ S() ];
    auto p = a.ptr;
    // extend until reallocation
    while (a.ptr == p)
        a.length = a.length + 1; // no assert    
}
---

This program should assert at runtime when the array is reallocated, but does not, because the copy constructors of the array's elements are not called.

If the copy constructor is changed to a postblit (`this(this)`), the program asserts at runtime, as expected.

See also issues 23557, 23556, and 20879, which cover array reallocations triggered by other means.