fix try_pod_read_unaligned... never having worked correctly (#138)

It seems like a copy-paste error has happened between `try_from_bytes`/`try_from_bytes_mut` and `try_pod_read_unaligned`, causing `internal::try_pod_read_unaligned` to try to read a &T::Bits instead of a T::Bits, usually failing with a `SizeMismatch` error. In the worst case, this allows UB in safe code by having a type allowing any bit pattern and being pointer-sized.

derive/tests/basic.rs

@@ -186,6 +186,21 @@ fn anybitpattern_implies_zeroable() {
   assert_eq!(test, AnyBitPatternTest { a: 0, b: 0 });
 }
 
+#[test]
+fn checkedbitpattern_try_pod_read_unaligned() {
+  let pod = [0u8];
+  let res = bytemuck::checked::try_pod_read_unaligned::<
+    CheckedBitPatternEnumWithValues,
+  >(&pod);
+  assert!(res.is_ok());
+
+  let pod = [5u8];
+  let res = bytemuck::checked::try_pod_read_unaligned::<
+    CheckedBitPatternEnumWithValues,
+  >(&pod);
+  assert!(res.is_err());
+}
+
 #[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
 #[repr(C, align(16))]
 struct Issue127 {}

src/checked.rs

@@ -249,7 +249,7 @@ pub fn try_pod_read_unaligned<T: CheckedBitPattern>(
 ) -> Result<T, CheckedCastError> {
   let pod = unsafe { internal::try_pod_read_unaligned(bytes) }?;
 
-  if <T as CheckedBitPattern>::is_valid_bit_pattern(pod) {
+  if <T as CheckedBitPattern>::is_valid_bit_pattern(&pod) {
     Ok(unsafe { transmute!(pod) })
   } else {
     Err(CheckedCastError::InvalidBitPattern)