Ensure no block ABI types have trailing padding

crates/block2/src/abi.rs

@@ -296,3 +296,26 @@ pub(crate) struct BlockDescriptorCopyDisposeSignature {
     #[doc(alias = "signature")]
     pub(crate) encoding: *const c_char,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn assert_no_trailing_padding<T>() {
+        struct AddU8<T> {
+            t: T,
+            extra: u8,
+        }
+        assert_ne!(core::mem::size_of::<T>(), core::mem::size_of::<AddU8<T>>());
+    }
+
+    #[test]
+    fn no_types_have_padding() {
+        assert_no_trailing_padding::<BlockHeader>();
+        assert_no_trailing_padding::<BlockDescriptorPtr>();
+        assert_no_trailing_padding::<BlockDescriptor>();
+        assert_no_trailing_padding::<BlockDescriptorCopyDispose>();
+        assert_no_trailing_padding::<BlockDescriptorSignature>();
+        assert_no_trailing_padding::<BlockDescriptorCopyDisposeSignature>();
+    }
+}