Compiler bug with struct<struct<bit>> where struct is the same struct but using a typedef

Take:

struct h<t>{
  t f;
}

typedef h<bit> tt;
typedef h<tt> t;

This produces:

In file: /home/apinski/src/p4/p4c/ir/visitor.h:351
Compiler Bug: IR loop detected

If instead of the two typedefs you do:

typedef h<h<bit>> t1;

You get:

header.p4(5): [--Werror=type-error] error: h: recursive type specialization
typedef h<h<bit>> t1;
          ^

But I don't see how this is not allowed even with the approved section in the last language design meeting.

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