presto-main/src/main/java/io/prestosql/metadata/SignatureBinder.java/SignatureBinder/appendConstraintSolversForReturnValue
class SignatureBinder:    private boolean appendConstraintSolversForReturnValue(ImmutableList.Builder<TypeConstraintSolver> resultBuilder, TypeSignatureProvider actualReturnType)
    {
        TypeSignature formalReturnTypeSignature = declaredSignature.getReturnType();
        return appendTypeRelationshipConstraintSolver(resultBuilder, formalReturnTypeSignature, actualReturnType, EXACT)
                && appendConstraintSolvers(resultBuilder, formalReturnTypeSignature, actualReturnType, false);
    }