Explicitly test Iterator::position overflows

src/libcore/iter/traits/iterator.rs

@@ -2069,15 +2069,14 @@ pub trait Iterator {
         Self: Sized,
         P: FnMut(Self::Item) -> bool,
     {
-        // The addition might panic on overflow
         #[inline]
-        #[rustc_inherit_overflow_checks]
         fn check<T>(
             mut predicate: impl FnMut(T) -> bool,
         ) -> impl FnMut(usize, T) -> LoopState<usize, usize> {
+            // The addition might panic on overflow
             move |i, x| {
                 if predicate(x) { LoopState::Break(i) }
-                else { LoopState::Continue(i + 1) }
+                else { LoopState::Continue(Add::add(i, 1)) }
             }
         }
 

src/test/run-pass/iterators/iter-position-overflow-debug.rs

@@ -0,0 +1,22 @@
+// run-pass
+// only-32bit too impatient for 2⁶⁴ items
+// ignore-wasm32-bare compiled with panic=abort by default
+// compile-flags: -C debug_assertions=yes
+
+use std::panic;
+use std::usize::MAX;
+
+fn main() {
+    let n = MAX as u64;
+    assert_eq!((0..).by_ref().position(|i| i >= n), Some(MAX));
+
+    let r = panic::catch_unwind(|| {
+        (0..).by_ref().position(|i| i > n)
+    });
+    assert!(r.is_err());
+
+    let r = panic::catch_unwind(|| {
+        (0..=n + 1).by_ref().position(|_| false)
+    });
+    assert!(r.is_err());
+}

src/test/run-pass/iterators/iter-position-overflow-ndebug.rs

@@ -0,0 +1,13 @@
+// run-pass
+// only-32bit too impatient for 2⁶⁴ items
+// compile-flags: -C debug_assertions=no
+
+use std::panic;
+use std::usize::MAX;
+
+fn main() {
+    let n = MAX as u64;
+    assert_eq!((0..).by_ref().position(|i| i >= n), Some(MAX));
+    assert_eq!((0..).by_ref().position(|i| i > n), Some(0));
+    assert_eq!((0..=n + 1).by_ref().position(|_| false), None);
+}