Function clause_obligations 

pub fn clause_obligations<'tcx>(
    infcx: &InferCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    body_id: LocalDefId,
    clause: Clause<'tcx>,
    span: Span,
) -> PredicateObligations<'tcx>

Returns the requirements for clause to be well-formed.

For example, if there is a trait Set defined like trait Set<K: Eq>, then the trait bound Foo: Set<Bar> is WF if Bar: Eq.