Recursive bounds loop the type checker

[nomeata]

func foo<A <: A>(x:A) : A { x };

is looping the type-checker.

[rossberg]

So is

type A = A

when used. Unproductive type recursion needs to be rejected.

[crusso]

For the CLR type bound checking, I think I implemented a simple check that tries to, given a binder with n related variables, tries to construct a path of length n by following type variable bounds only.
If you can, then the definition is acylic. If we can rely on type definitions being productive (so we don't have to unfold definition in bounds such as A <: T ?) that may work here too.

[nomeata]

If #155 is a duplicate of #76, then this is too. Closing this and #155 to have less tickets to migrate to JIRA.

[nomeata]

Actually, no, they are slightly different. Anyways, I’ll create a JIRA ticket.

[nomeata]

Now at https://dfinity.atlassian.net/browse/AST-19