1 files changed, 44 insertions, 0 deletions
diff --git a/library/core/tests/alloc.rs b/library/core/tests/alloc.rs
index 8a5a06b34..3ceaeadce 100644
--- a/library/core/tests/alloc.rs
+++ b/library/core/tests/alloc.rs
@@ -1,4 +1,5 @@
 use core::alloc::Layout;
+use core::mem::size_of;
 use core::ptr::{self, NonNull};
 
 #[test]
@@ -13,6 +14,49 @@ fn const_unchecked_layout() {
 }
 
 #[test]
+fn layout_round_up_to_align_edge_cases() {
+    const MAX_SIZE: usize = isize::MAX as usize;
+
+    for shift in 0..usize::BITS {
+        let align = 1_usize << shift;
+        let edge = (MAX_SIZE + 1) - align;
+        let low = edge.saturating_sub(10);
+        let high = edge.saturating_add(10);
+        assert!(Layout::from_size_align(low, align).is_ok());
+        assert!(Layout::from_size_align(high, align).is_err());
+        for size in low..=high {
+            assert_eq!(
+                Layout::from_size_align(size, align).is_ok(),
+                size.next_multiple_of(align) <= MAX_SIZE,
+            );
+        }
+    }
+}
+
+#[test]
+fn layout_array_edge_cases() {
+    for_type::<i64>();
+    for_type::<[i32; 0b10101]>();
+    for_type::<[u8; 0b1010101]>();
+
+    // Make sure ZSTs don't lead to divide-by-zero
+    assert_eq!(Layout::array::<()>(usize::MAX).unwrap(), Layout::from_size_align(0, 1).unwrap());
+
+    fn for_type<T>() {
+        const MAX_SIZE: usize = isize::MAX as usize;
+
+        let edge = (MAX_SIZE + 1) / size_of::<T>();
+        let low = edge.saturating_sub(10);
+        let high = edge.saturating_add(10);
+        assert!(Layout::array::<T>(low).is_ok());
+        assert!(Layout::array::<T>(high).is_err());
+        for n in low..=high {
+            assert_eq!(Layout::array::<T>(n).is_ok(), n * size_of::<T>() <= MAX_SIZE);
+        }
+    }
+}
+
+#[test]
 fn layout_debug_shows_log2_of_alignment() {
     // `Debug` is not stable, but here's what it does right now
     let layout = Layout::from_size_align(24576, 8192).unwrap();