[I] `MutableArrayData::extend` ignores the offset of `FixedSizeList` `ArrayData` [arrow-rs]

["mbutrovich (via GitHub)" <gi...@apache.org>]

mbutrovich opened a new issue, #11588:
URL: https://github.com/apache/arrow-rs/issues/11588

   ### Describe the bug
   
   Extending from `FixedSizeList` `ArrayData` that has a nonzero offset copies the child values from the start of the child rather than from the offset.
   
   ### To Reproduce
   
   ```rust
   use std::sync::Arc;
   use arrow_array::{make_array, Array, ArrayRef, FixedSizeListArray, Int32Array};
   use arrow_data::transform::MutableArrayData;
   use arrow_schema::{DataType, Field};
   
   fn main() {
       // Rows [[0, 1], [2, 3], [4, 5]], with offset 1 and length 2 on the parent
       let child: ArrayRef = Arc::new(Int32Array::from(vec![0, 1, 2, 3, 4, 5]));
       let list = FixedSizeListArray::new(Arc::new(Field::new("item", DataType::Int32, true)), 2, child, None);
       let data = list.to_data().into_builder().offset(1).len(2).build().unwrap();
   
       let mut m = MutableArrayData::new(vec![&data], false, 2);
       m.try_extend(0, 0, 2).unwrap();
       let out = make_array(m.freeze());
       let out = out.as_any().downcast_ref::<FixedSizeListArray>().unwrap();
       println!("{:?}", out.values()); // [0, 1, 2, 3], expected [2, 3, 4, 5]
   }
   ```
   
   ### Expected behavior
   
   The result holds the rows at offset 1, `[[2, 3], [4, 5]]`, as `make_array(data)` does.
   
   ### Additional context
   
   `build_extend` extends the child from `start * size` and does not add `array.offset()` ([fixed_size_list.rs](https://github.com/apache/arrow-rs/blob/72887ed91c80002bb7ec755ce1e964bab07bebea/arrow-data/src/transform/fixed_size_list.rs#L23-L36)). #10933 fixed the same issue for structs in `transform/structure.rs`.
   
   `Array::slice` never produces this layout, because `FixedSizeListArray` slices its child. It arrives from FFI producers, which may set the offset on the parent and leave the child whole ([CDataInterface.rst](https://github.com/apache/arrow/blob/6b4c5248127881c506d4e21e6c95a5c4ced5d0d4/docs/source/format/CDataInterface.rst?plain=1#L456-L459)), and from code that builds `ArrayData` with an offset.
   
   Found with property-based tests that build arrays in every physical layout the Arrow format allows.
   


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Re: [I] `MutableArrayData::extend` ignores the offset of `FixedSizeList` `ArrayData` [arrow-rs]

["Jefffrey (via GitHub)" <gi...@apache.org>]

Jefffrey closed issue #11588: `MutableArrayData::extend` ignores the offset of `FixedSizeList` `ArrayData`
URL: https://github.com/apache/arrow-rs/issues/11588


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Re: [I] `MutableArrayData::extend` ignores the offset of `FixedSizeList` `ArrayData` [arrow-rs]

["ahlag (via GitHub)" <gi...@apache.org>]

ahlag commented on issue #11588:
URL: https://github.com/apache/arrow-rs/issues/11588#issuecomment-6227524051

   I'd like to take this. Draft fix in #11636: `build_extend` now adds `array.offset()` to `start`, as #10934 did for structs, with a unit test next to the struct one. I'll mark it ready for review once CI passes.


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