refactor: add Expression::coalesce helper method #1648
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This was referenced Jan 21, 2026
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #1648 +/- ##
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Branches 34114 34109 -5
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## 🥞 Stacked PR Use this [link](https://github.com/delta-io/delta-kernel-rs/pull/1645/files) to review incremental changes. - [**stack/null-propagation**](#1645) [[Files changed](https://github.com/delta-io/delta-kernel-rs/pull/1645/files)] - [stack/coalesce](#1648) [[Files changed](https://github.com/delta-io/delta-kernel-rs/pull/1648/files/37e755009566511bf7c2f00e014c1647e77e4533..d64042f7908844ef2d8a1c68312dc3ff936d60dc)] - [stack/checkpoint-transforms](#1646) [[Files changed](https://github.com/delta-io/delta-kernel-rs/pull/1646/files/d64042f7908844ef2d8a1c68312dc3ff936d60dc..4e66ca004f89b23431a96ac106a9c0d400718b10)] - [stack/write-stats](#1643) [[Files changed](https://github.com/delta-io/delta-kernel-rs/pull/1643/files/4e66ca004f89b23431a96ac106a9c0d400718b10..cd64f79fd3b40ebfa811cb333369cb17aa1a2a74)] --------- ## What changes are proposed in this pull request? Fixes a bug in nested transform expression evaluation where null rows in the source struct were losing their null bitmap, causing null structs to incorrectly appear as non-null structs with null fields. When evaluating nested transform expressions (transforms with an input_path that operate on a nested struct), the output StructArray was created with None for the null buffer: `let data = StructArray::try_new(output_fields.into(), output_cols, None)?;` This meant that if the source struct had null rows (e.g., an add action that is null in a checkpoint batch), the output would lose that null information. The struct would appear as non-null but with all-null fields, which is semantically different. ## How was this change tested? Existing transform tests pass. The stats transform integration tests (in a follow-up PR) exercise this code path.
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🥞 Stacked PR
Use this link to review incremental changes.
What changes are proposed in this pull request?
This PR adds an
Expression::coalescehelper method to simplify creating COALESCE expressions, and updates all existing call sites to use the new helper.How was this change tested?
Existing tests