Add unsafe to Array trait and SAFETY commands in all unsafe impl Array

Author: gabotechs

arrow-array/src/array/boolean_array.rs

@@ -286,7 +286,8 @@ impl BooleanArray {
     }
 }
 
-impl Array for BooleanArray {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl Array for BooleanArray {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/byte_array.rs

@@ -462,7 +462,8 @@ impl<T: ByteArrayType> std::fmt::Debug for GenericByteArray<T> {
     }
 }
 
-impl<T: ByteArrayType> Array for GenericByteArray<T> {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl<T: ByteArrayType> Array for GenericByteArray<T> {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/byte_view_array.rs

@@ -885,7 +885,8 @@ impl<T: ByteViewType + ?Sized> Debug for GenericByteViewArray<T> {
     }
 }
 
-impl<T: ByteViewType + ?Sized> Array for GenericByteViewArray<T> {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl<T: ByteViewType + ?Sized> Array for GenericByteViewArray<T> {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/dictionary_array.rs

@@ -692,7 +692,8 @@ impl<'a, T: ArrowDictionaryKeyType> FromIterator<&'a str> for DictionaryArray<T>
     }
 }
 
-impl<T: ArrowDictionaryKeyType> Array for DictionaryArray<T> {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl<T: ArrowDictionaryKeyType> Array for DictionaryArray<T> {
     fn as_any(&self) -> &dyn Any {
         self
     }
@@ -851,7 +852,7 @@ impl<'a, K: ArrowDictionaryKeyType, V> TypedDictionaryArray<'a, K, V> {
     }
 }
 
-impl<K: ArrowDictionaryKeyType, V: Sync> Array for TypedDictionaryArray<'_, K, V> {
+unsafe impl<K: ArrowDictionaryKeyType, V: Sync> Array for TypedDictionaryArray<'_, K, V> {
     fn as_any(&self) -> &dyn Any {
         self.dictionary
     }

arrow-array/src/array/fixed_size_binary_array.rs

@@ -602,7 +602,8 @@ impl std::fmt::Debug for FixedSizeBinaryArray {
     }
 }
 
-impl Array for FixedSizeBinaryArray {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl Array for FixedSizeBinaryArray {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/fixed_size_list_array.rs

@@ -462,7 +462,8 @@ impl From<FixedSizeListArray> for ArrayData {
     }
 }
 
-impl Array for FixedSizeListArray {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl Array for FixedSizeListArray {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/list_array.rs

@@ -527,7 +527,8 @@ impl<OffsetSize: OffsetSizeTrait> GenericListArray<OffsetSize> {
     }
 }
 
-impl<OffsetSize: OffsetSizeTrait> Array for GenericListArray<OffsetSize> {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl<OffsetSize: OffsetSizeTrait> Array for GenericListArray<OffsetSize> {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/list_view_array.rs

@@ -415,7 +415,8 @@ impl<OffsetSize: OffsetSizeTrait> ArrayAccessor for &GenericListViewArray<Offset
     }
 }
 
-impl<OffsetSize: OffsetSizeTrait> Array for GenericListViewArray<OffsetSize> {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl<OffsetSize: OffsetSizeTrait> Array for GenericListViewArray<OffsetSize> {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/map_array.rs

@@ -362,7 +362,8 @@ impl MapArray {
     }
 }
 
-impl Array for MapArray {
+/// SAFETY: Correctly implements the contract of Arrow Arrays
+unsafe impl Array for MapArray {
     fn as_any(&self) -> &dyn Any {
         self
     }

arrow-array/src/array/mod.rs

@@ -79,7 +79,16 @@ pub use list_view_array::*;
 use crate::iterator::ArrayIter;
 
 /// An array in the [arrow columnar format](https://arrow.apache.org/docs/format/Columnar.html)
-pub trait Array: std::fmt::Debug + Send + Sync {
+///
+/// # Safety
+///
+/// Implementations of this trait must ensure that all methods implementations comply with
+/// the Arrow specification. No safety guards are placed and failing to comply with it can
+/// translate into panics or undefined behavior. For example, a value computed based on `len`
+/// may be used as a direct index into memory regions without checks.
+///
+/// Use it at your own risk knowing that this trait might be sealed in the future.
+pub unsafe trait Array: std::fmt::Debug + Send + Sync {
     /// Returns the array as [`Any`] so that it can be
     /// downcasted to a specific implementation.
     ///
@@ -342,7 +351,7 @@ pub trait Array: std::fmt::Debug + Send + Sync {
 pub type ArrayRef = Arc<dyn Array>;
 
 /// Ergonomics: Allow use of an ArrayRef as an `&dyn Array`
-impl Array for ArrayRef {
+unsafe impl Array for ArrayRef {
     fn as_any(&self) -> &dyn Any {
         self.as_ref().as_any()
     }
@@ -421,7 +430,7 @@ impl Array for ArrayRef {
     }
 }
 
-impl<T: Array> Array for &T {
+unsafe impl<T: Array> Array for &T {
     fn as_any(&self) -> &dyn Any {
         T::as_any(self)
     }