Expose the null buffer of every builder that has one (#5754)

Author: HadrienG2

arrow-array/src/builder/fixed_size_binary_builder.rs

@@ -115,6 +115,11 @@ impl FixedSizeBinaryBuilder {
         let array_data = unsafe { array_data_builder.build_unchecked() };
         FixedSizeBinaryArray::from(array_data)
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.null_buffer_builder.as_slice()
+    }
 }
 
 impl ArrayBuilder for FixedSizeBinaryBuilder {

arrow-array/src/builder/fixed_size_list_builder.rs

@@ -208,6 +208,11 @@ where
 
         FixedSizeListArray::new(field, self.list_len, values, nulls)
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.null_buffer_builder.as_slice()
+    }
 }
 
 #[cfg(test)]

arrow-array/src/builder/generic_bytes_dictionary_builder.rs

@@ -299,6 +299,11 @@ where
 
         DictionaryArray::from(unsafe { builder.build_unchecked() })
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.keys_builder.validity_slice()
+    }
 }
 
 impl<K: ArrowDictionaryKeyType, T: ByteArrayType, V: AsRef<T::Native>> Extend<Option<V>>

arrow-array/src/builder/generic_bytes_view_builder.rs

@@ -146,6 +146,11 @@ impl<T: ByteViewType + ?Sized> GenericByteViewBuilder<T> {
         // SAFETY: valid by construction
         unsafe { GenericByteViewArray::new_unchecked(views, completed, nulls) }
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.null_buffer_builder.as_slice()
+    }
 }
 
 impl<T: ByteViewType + ?Sized> Default for GenericByteViewBuilder<T> {

arrow-array/src/builder/generic_list_builder.rs

@@ -326,6 +326,11 @@ where
     pub fn offsets_slice(&self) -> &[OffsetSize] {
         self.offsets_builder.as_slice()
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.null_buffer_builder.as_slice()
+    }
 }
 
 impl<O, B, V, E> Extend<Option<V>> for GenericListBuilder<O, B>

arrow-array/src/builder/map_builder.rs

@@ -226,6 +226,11 @@ impl<K: ArrayBuilder, V: ArrayBuilder> MapBuilder<K, V> {
 
         MapArray::from(array_data)
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.null_buffer_builder.as_slice()
+    }
 }
 
 impl<K: ArrayBuilder, V: ArrayBuilder> ArrayBuilder for MapBuilder<K, V> {

arrow-array/src/builder/primitive_dictionary_builder.rs

@@ -302,6 +302,11 @@ where
     pub fn values_slice_mut(&mut self) -> &mut [V::Native] {
         self.values_builder.values_slice_mut()
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.keys_builder.validity_slice()
+    }
 }
 
 impl<K: ArrowDictionaryKeyType, P: ArrowPrimitiveType> Extend<Option<P::Native>>

arrow-array/src/builder/struct_builder.rs

@@ -381,6 +381,11 @@ impl StructBuilder {
             }
         });
     }
+
+    /// Returns the current null buffer as a slice
+    pub fn validity_slice(&self) -> Option<&[u8]> {
+        self.null_buffer_builder.as_slice()
+    }
 }
 
 #[cfg(test)]