Seal Array trait (#9092)

# Which issue does this PR close?

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- Closes #9106

# Rationale for this change

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in the issue then this section is not needed.
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This trait is not meant to be overridden, and doing so will break many
kernels in sometimes subtle ways.

# What changes are included in this PR?

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PR.
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Seals the Array trait to prevent implementation outside of arrow-array.

# Are these changes tested?

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# Are there any user-facing changes?

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---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: tustvold

arrow-array/src/array/boolean_array.rs

@@ -286,6 +286,8 @@ impl BooleanArray {
     }
 }
 
+impl super::private::Sealed for BooleanArray {}
+
 impl Array for BooleanArray {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/byte_array.rs

@@ -462,6 +462,8 @@ impl<T: ByteArrayType> std::fmt::Debug for GenericByteArray<T> {
     }
 }
 
+impl<T: ByteArrayType> super::private::Sealed for GenericByteArray<T> {}
+
 impl<T: ByteArrayType> Array for GenericByteArray<T> {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/byte_view_array.rs

@@ -854,6 +854,8 @@ impl<T: ByteViewType + ?Sized> Debug for GenericByteViewArray<T> {
     }
 }
 
+impl<T: ByteViewType + ?Sized> super::private::Sealed for GenericByteViewArray<T> {}
+
 impl<T: ByteViewType + ?Sized> Array for GenericByteViewArray<T> {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/dictionary_array.rs

@@ -697,6 +697,8 @@ impl<'a, T: ArrowDictionaryKeyType> FromIterator<&'a str> for DictionaryArray<T>
     }
 }
 
+impl<T: ArrowDictionaryKeyType> super::private::Sealed for DictionaryArray<T> {}
+
 impl<T: ArrowDictionaryKeyType> Array for DictionaryArray<T> {
     fn as_any(&self) -> &dyn Any {
         self
@@ -856,6 +858,8 @@ impl<'a, K: ArrowDictionaryKeyType, V> TypedDictionaryArray<'a, K, V> {
     }
 }
 
+impl<K: ArrowDictionaryKeyType, V: Sync> super::private::Sealed for TypedDictionaryArray<'_, K, V> {}
+
 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

@@ -602,6 +602,8 @@ impl std::fmt::Debug for FixedSizeBinaryArray {
     }
 }
 
+impl super::private::Sealed for FixedSizeBinaryArray {}
+
 impl Array for FixedSizeBinaryArray {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/fixed_size_list_array.rs

@@ -462,6 +462,8 @@ impl From<FixedSizeListArray> for ArrayData {
     }
 }
 
+impl super::private::Sealed for FixedSizeListArray {}
+
 impl Array for FixedSizeListArray {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/list_array.rs

@@ -525,6 +525,8 @@ impl<OffsetSize: OffsetSizeTrait> GenericListArray<OffsetSize> {
     }
 }
 
+impl<OffsetSize: OffsetSizeTrait> super::private::Sealed for GenericListArray<OffsetSize> {}
+
 impl<OffsetSize: OffsetSizeTrait> Array for GenericListArray<OffsetSize> {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/list_view_array.rs

@@ -415,6 +415,8 @@ impl<OffsetSize: OffsetSizeTrait> ArrayAccessor for &GenericListViewArray<Offset
     }
 }
 
+impl<OffsetSize: OffsetSizeTrait> super::private::Sealed for GenericListViewArray<OffsetSize> {}
+
 impl<OffsetSize: OffsetSizeTrait> Array for GenericListViewArray<OffsetSize> {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/map_array.rs

@@ -361,6 +361,8 @@ impl MapArray {
     }
 }
 
+impl super::private::Sealed for MapArray {}
+
 impl Array for MapArray {
     fn as_any(&self) -> &dyn Any {
         self

arrow-array/src/array/mod.rs

@@ -78,8 +78,18 @@ pub use list_view_array::*;
 
 use crate::iterator::ArrayIter;
 
+mod private {
+    /// Private marker trait to ensure [`super::Array`] can not be implemented outside this crate
+    pub trait Sealed {}
+
+    impl<T: Sealed> Sealed for &T {}
+}
+
 /// An array in the [arrow columnar format](https://arrow.apache.org/docs/format/Columnar.html)
-pub trait Array: std::fmt::Debug + Send + Sync {
+///
+/// This trait is sealed as it is not intended for custom array types, rather only
+/// those defined in this crate.
+pub trait Array: std::fmt::Debug + Send + Sync + private::Sealed {
     /// Returns the array as [`Any`] so that it can be
     /// downcasted to a specific implementation.
     ///
@@ -341,6 +351,8 @@ pub trait Array: std::fmt::Debug + Send + Sync {
 /// A reference-counted reference to a generic `Array`
 pub type ArrayRef = Arc<dyn Array>;
 
+impl private::Sealed for ArrayRef {}
+
 /// Ergonomics: Allow use of an ArrayRef as an `&dyn Array`
 impl Array for ArrayRef {
     fn as_any(&self) -> &dyn Any {