sunchao commented on PR #5654:
URL: 
https://github.com/apache/datafusion-comet/pull/5654#issuecomment-5654386714

   Reviewed head `1ea1be161` against base `db790673d`. **I found one P2 
correctness regression to fix before merging.**
   
   ### P2: Duplicate root names now select the wrong column
   
   The new [root-field 
shadowing](https://github.com/apache/datafusion-comet/blob/1ea1be161ec664b8705b109be5004593a5d7bb4f/native/core/src/parquet/schema_adapter.rs#L348)
 hides earlier duplicate names and selects the last column.
   
   I tested one Parquet file containing two separate `d` columns, reading it 
with explicit schema `d bigint` and case sensitivity enabled:
   
   | Reader | Result |
   |---|---|
   | Spark 4.1.3, vectorized | `[1, 2, 3]` |
   | Base native scan harness | `[1, 2, 3]` |
   | PR native scan harness | `[10, 20, 30]` |
   
   This changes previously matching results. Spark’s schema-clipping `.toMap` 
behavior does not establish what its reader actually returns. Preserve the 
working root-column selection and add a comparison against Spark using the same 
file.
   
   This supplies concrete differential evidence for the concern already 
discussed in [#5884](https://github.com/apache/datafusion-comet/issues/5884).
   
   ### Validation and remaining assessment
   
   - **CI:** 56 successful, 10 skipped; `Required Checks` passed.
   - **Local:** 22 component tests passed. Additional scan probes verified the 
earlier default-value and duplicate-ID fixes.
   - **Build limit:** The registry lacks pinned DataFusion 55.1. Native probes 
used current changed modules with DataFusion 55.0 / Arrow 59.3, rather than a 
full current-head Comet build. Relevant upstream root-read paths were checked 
against 55.1.
   - No other actionable findings emerged from mapping, projection, ownership, 
footer-cache, or JNI-error review.
   
   Evidence: Spark result, base result, PR result (local reproduction logs).
   
   Nothing was published to GitHub.
   


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