docs: add documentation for complex type cast support #2990
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This adds documentation for native support of complex type casts including STRUCT to STRING/STRUCT, ARRAY to STRING, and BINARY to/from STRING conversions. Closes apache#2743
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Pull request overview
This PR adds comprehensive documentation for complex type cast operations to the Comet compatibility guide, addressing issue #2743. The documentation clarifies which complex type casts (STRUCT, ARRAY, BINARY) are natively supported by Comet and which will fall back to Spark.
Key changes:
- Added "Complex Type Casts" section documenting native support for STRUCT→STRING, STRUCT→STRUCT, ARRAY→STRING, BINARY→STRING, and STRING→BINARY casts
- Included practical SQL examples for each supported cast type
- Documented known limitations and fallback behavior for unsupported complex casts
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PR Description
Which issue does this PR close?
Closes #2743
Rationale for this change
Comet already provides native support for a subset of cast operations involving complex types such as STRUCT and ARRAY, but this behavior was not documented in the compatibility guide. As a result, users may be unaware of which complex type casts are supported natively and which may fall back to Spark.
This change improves the accuracy and completeness of the documentation by explicitly describing the currently supported complex type casts and their limitations, based on existing behavior and tests.
What changes are included in this PR?
STRUCT→STRING(including named structs, nested structs, and structs containing primitive, decimal, date, and timestamp fields)STRUCT→STRUCT(field matching by position)ARRAY<T>→STRING(for element types: boolean, byte, short, integer, long, string, decimal)BINARY→STRING(for valid UTF-8 data)STRING→BINARYHow are these changes tested?
This PR only updates documentation. The documented behavior is verified against existing tests in
CometCastSuite.scala, which cover the supported complex type cast operations:test("cast StructType to StringType")- lines 1090-1110test("cast StructType to StructType")- lines 1112-1123test("cast StructType to StructType with different names")- lines 1125-1141test("cast ArrayType to StringType")- lines 1164-1184test("cast BinaryType to StringType")- lines 895-897test("cast StringType to BinaryType")- lines 847-849No new tests are required for this documentation-only change.