The following code compiles with dmd 2.086.0, but not with dmd 2.086.1 or dmd 2.088.0-beta.1:

class Context
{
    size_t[const(Key)] aa;
    bool checkAll;
}

struct Key
{
    Context context;
    int i;
    bool opEquals(ref const Key other) const
    {
        if(context.checkAll && i != other.i)
            return false;
        return true;
    }
}

Dmd 2.086.1 prints the following error message:
Error: AA key type Key does not have bool opEquals(ref const Key) const