cmd/vet: copylock: infinite recursion through type parameters

[findleyr]

We need to be careful to avoid infinite recursion in recursive vet checks that consider type parameters. The following code causes an infinite recursion in the new copylock logic (discovered when gopls crashed while working on similar handling for infinite recursion in the printf analyzer...).

func TestRecursiveTypeParams[T1 ~[]T2, T2 ~[]T1 | string, T3 ~struct{ F T3 }](t1 T1, t2 T2, t3 T3) {
}

I'll audit the other updated vet analyzers for similar problems.

CC @timothy-king

[gopherbot]

Change https://golang.org/cl/361456 mentions this issue: go/analysis/passes/copylock: avoid infinite recursion via type params

[findleyr]

Ok, I looked at all other places where we consider the structural terms of a type parameter, and they do not recurse. So CL 361456 should be sufficient.