cmd/compile: cannot compile valid (but esoteric) self-recursive interface

[griesemer]

https://play.golang.org/p/YSkuYfVQHI

Esoteric case. Just for reference.

[griesemer]

This is just one case of whole class of errors of recursive types referring to themselves via an array type that depends on the size of an aspect of the recursive type.

A possible general solution might be to defer all array size computations to the end of type-checking, similarly to how we defer map key type-checking to the end.