gistfile1.cs

public static class MyExtensions {
  	public IRuleBuilderOptions<T, TProperty> SetValidator<T, TProperty>(this IRuleBuilder<T, TProperty> ruleBuilder, Func<T, IValidator<TProperty>> validatorThunk) {
			return ruleBuilder.SetValidator(new LazyValidatorAdaptor<T, TProperty>(validatorThunk));
		}

		private class LazyValidatorAdaptor<T, TProperty> : NoopPropertyValidator {
			Func<T, IValidator<TProperty>> _validatorThunk;

			public LazyValidatorAdaptor(Func<T, IValidator<TProperty>> validatorThunk) {
				_validatorThunk = validatorThunk;
			}

			public override IEnumerable<ValidationFailure> Validate(PropertyValidatorContext context) {
				var validator = _validatorThunk((T)context.Instance);
				var adaptor = new ChildValidatorAdaptor(validator);
				return adaptor.Validate(context);
			}
		}
	}
  
  // Useable like this:
  // RuleFor(x => x.Foo).SetValidator(x => new FooValidator(x));

So, this would apply the child validator, then allow me to chain on subsequent rules, and assumes I'd set CascadeMode to StopOnFirstFailure...?

Something like (coding from memory; currently offsite):

RuleFor(x => x.Tenant).SetValidator(new TenantValidator()); // make sure tenant is cool
RuleFor(x => x.Foo)
  .SetValidator(x => new FooValidator(x)); // only fires if Tenant is valid...?

Not sure I've followed, sorry.