Cover equal-size alignment mismatches

src/tests.rs

@@ -7,6 +7,7 @@ use super::*;
 use std::alloc::Layout;
 use std::cell::Cell;
 use std::marker::PhantomData;
+use std::mem::{align_of, size_of};
 use std::panic;
 use std::rc::Rc;
 use std::sync::Arc;
@@ -807,6 +808,33 @@ fn test_aligned_zst_layout_mismatch_is_non_destructive() {
     assert_eq!(erased.capacity(), usize::MAX);
 }
 
+#[test]
+fn test_equal_size_different_alignment_is_rejected() {
+    #[repr(align(8))]
+    struct AlignEight([u8; 8]);
+
+    assert_eq!(size_of::<AlignEight>(), size_of::<[u8; 8]>());
+    assert_ne!(align_of::<AlignEight>(), align_of::<[u8; 8]>());
+
+    let values = vec![AlignEight([1, 2, 3, 4, 5, 6, 7, 8])];
+    let original_ptr = values.as_ptr();
+    let original_capacity = values.capacity();
+    let mut erased = TypeErasedVec::new(values);
+
+    assert!(erased.try_as_type::<[u8; 8]>().is_none());
+    assert!(erased.try_as_type_scoped::<[u8; 8]>().is_none());
+    assert_erased_state(&erased, 1, Layout::new::<AlignEight>());
+    assert_eq!(erased.capacity(), original_capacity);
+
+    // SAFETY: Both failed probes preserved the original element type.
+    let guard = unsafe { erased.cast_type::<AlignEight>() };
+    assert_eq!(guard.as_slice().as_ptr(), original_ptr);
+    assert_eq!(
+        guard.as_slice().first().map(|value| value.0),
+        Some([1, 2, 3, 4, 5, 6, 7, 8])
+    );
+}
+
 #[test]
 fn test_scoped_borrowed_zst_behavior() {
     struct BorrowedZst<'a>(PhantomData<&'a u8>);