make slice work for nested types

revert changes made in ARROW-11394

See commit 9f96561

Only slice into structs

Author: nevi-me

arrow/src/array/array_struct.rs

@@ -84,12 +84,7 @@ impl From<ArrayData> for StructArray {
     fn from(data: ArrayData) -> Self {
         let mut boxed_fields = vec![];
         for cd in data.child_data() {
-            let child_data = if data.offset() != 0 || data.len() != cd.len() {
-                cd.slice(data.offset(), data.len())
-            } else {
-                cd.clone()
-            };
-            boxed_fields.push(make_array(child_data));
+            boxed_fields.push(make_array(cd.clone()));
         }
         Self { data, boxed_fields }
     }

arrow/src/array/data.rs

@@ -383,15 +383,36 @@ impl ArrayData {
     pub fn slice(&self, offset: usize, length: usize) -> ArrayData {
         assert!((offset + length) <= self.len());
 
-        let mut new_data = self.clone();
-
-        new_data.len = length;
-        new_data.offset = offset + self.offset;
-
-        new_data.null_count =
-            count_nulls(new_data.null_buffer(), new_data.offset, new_data.len);
-
-        new_data
+        if let DataType::Struct(_) = self.data_type() {
+            // Slice into children
+            let new_offset = self.offset + offset;
+            let new_data = ArrayData {
+                data_type: self.data_type().clone(),
+                len: length,
+                null_count: count_nulls(self.null_buffer(), new_offset, length),
+                offset: new_offset,
+                buffers: self.buffers.clone(),
+                // Slice child data, to propagate offsets down to them
+                child_data: self
+                    .child_data()
+                    .iter()
+                    .map(|data| data.slice(offset, length))
+                    .collect(),
+                null_bitmap: self.null_bitmap().clone(),
+            };
+
+            new_data
+        } else {
+            let mut new_data = self.clone();
+
+            new_data.len = length;
+            new_data.offset = offset + self.offset;
+
+            new_data.null_count =
+                count_nulls(new_data.null_buffer(), new_data.offset, new_data.len);
+
+            new_data
+        }
     }
 
     /// Returns the `buffer` as a slice of type `T` starting at self.offset

arrow/src/array/transform/structure.rs

@@ -26,13 +26,10 @@ pub(super) fn build_extend(array: &ArrayData) -> Extend {
                   index: usize,
                   start: usize,
                   len: usize| {
-                mutable.child_data.iter_mut().for_each(|child| {
-                    child.extend(
-                        index,
-                        array.offset() + start,
-                        array.offset() + start + len,
-                    )
-                })
+                mutable
+                    .child_data
+                    .iter_mut()
+                    .for_each(|child| child.extend(index, start, start + len))
             },
         )
     } else {
@@ -41,7 +38,7 @@ pub(super) fn build_extend(array: &ArrayData) -> Extend {
                   index: usize,
                   start: usize,
                   len: usize| {
-                (array.offset() + start..array.offset() + start + len).for_each(|i| {
+                (start..start + len).for_each(|i| {
                     if array.is_valid(i) {
                         mutable
                             .child_data