remap

    fn remap(
        ctx: *anyopaque,
        memory: []u8,
        alignment: Alignment,
        new_len: usize,
        return_address: usize,
    ) ?[*]u8 {
        assert(new_len > 0);
        // Prefer resizing in-place if possible, since `realloc` could be expensive even if legal.
        if (resize(ctx, memory, alignment, new_len, return_address)) {
            return memory.ptr;
        }
        switch (allocStrat(alignment)) {
            .raw => {
                // `malloc` and friends guarantee the required alignment, so we can try `realloc`.
                // C only needs to respect `max_align_t` up to the allocation size due to object
                // alignment rules. If necessary, extend the allocation size.
                const actual_len = @max(new_len, @alignOf(std.c.max_align_t));
                const new_ptr = c.realloc(memory.ptr, actual_len) orelse return null;
                assert(alignment.check(@intFromPtr(new_ptr)));
                return @ptrCast(new_ptr);
            },
            .posix_memalign, .manual_align => {
                // `realloc` would potentially return a new allocation which does not respect
                // the original alignment, so we can't do anything more.
                return null;
            },
        }
    }