7464 – Better Error Message When Using S.tupleof within S

struct S {
 static if(hasIndirections!(typeof(this))) {}
}
template hasIndirections(T)
{
 enum hasIndirections = hasIndirectionsImpl!(typeof(T.init.tupleof));
}
template hasIndirectionsImpl(T...)
{
 static if (!T.length)
 {
 enum hasIndirectionsImpl = false;
 }
 else
 {
 enum hasIndirectionsImpl = true;
 }
}
This is wrong because S isn't fully defined yet, so S.init.tupleof makes no sense. However, the error message is extremely obtuse:
Error: struct S no size yet for forward reference

The new diagnostic is:
-----
test.d(2): Error: forward reference of variable hasIndirections
test.d(2): Error: template instance test.hasIndirections!(S) error instantiating
-----
But I'm not sure this is better.

FWIW, the code compiled before https://github.com/dlang/dmd/pull/595.

compiles since 2.080 but AFAIU this should not

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