Add type invariant

Author: tautschnig

library/core/src/iter/adapters/step_by.rs

@@ -1,11 +1,10 @@
-use safety::requires;
-
 use crate::intrinsics;
 use crate::iter::{TrustedLen, TrustedRandomAccess, from_fn};
 #[cfg(kani)]
 use crate::kani;
 use crate::num::NonZero;
 use crate::ops::{Range, Try};
+use crate::ub_checks::Invariant;
 
 /// An iterator for stepping iterators by a custom amount.
 ///
@@ -33,6 +32,12 @@ pub struct StepBy<I> {
     first_take: bool,
 }
 
+impl<I> Invariant for StepBy<I> {
+    fn is_safe(&self) -> bool {
+        step_minus_one < usize::MAX
+    }
+}
+
 impl<I> StepBy<I> {
     #[inline]
     pub(in crate::iter) fn new(iter: I, step: usize) -> StepBy<I> {