[GitHub] [arrow-rs] tustvold commented on a diff in pull request #2883: Skip memory alignment check when constructing PrimitiveArray from an array data reference

[GitBox]

tustvold commented on code in PR #2883:
URL: https://github.com/apache/arrow-rs/pull/2883#discussion_r996382149


##########
arrow-array/src/array/list_array.rs:
##########
@@ -861,16 +861,40 @@ mod tests {
     }
 
     #[test]
-    #[should_panic(expected = "memory is not aligned")]
+    #[should_panic(expected = "Need at least 8 bytes in buffers[0]")]
     fn test_primitive_array_alignment() {
-        let ptr = arrow_buffer::alloc::allocate_aligned(8);
+        let ptr = arrow_buffer::alloc::allocate_aligned_zeroed(8);
         let buf = unsafe { Buffer::from_raw_parts(ptr, 8, 8) };
+        let buf1 = buf.slice(1);
         let buf2 = buf.slice(1);
+
+        // Aligned
+        let array_data = ArrayData::builder(DataType::Int32)
+            .add_buffer(buf)
+            .len(2)
+            .build()
+            .unwrap();
+        let array = Int32Array::from(array_data);
+        assert_eq!(array.len(), 2);
+        assert_eq!(array.value(0), 0);
+        assert_eq!(array.value(1), 0);
+
+        // Not aligned.
+        // `ArrayData::build` checks buffer length.
         let array_data = ArrayData::builder(DataType::Int32)
+            .add_buffer(buf1)
+            .len(1)
+            .build()
+            .unwrap();
+        let array = Int32Array::from(array_data);
+        assert_eq!(array.len(), 1);
+        assert_eq!(array.value(0), 0);

Review Comment:
   This is now UB, as this violates the safety requirement in 
PrimitiveArray::values.
   
   I'm not sure why MIRI isn't catching this...
   
   Edit: `array.value` doesn't call `array.values` so this test isn't UB. If 
you add a call to `array.values()` in this test, MIRI will fail



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