Expose hidden JVM function execution inside native Calc

[ChaomingZhangCN]

Why

A NativeCalc or NativeFilter in the physical plan does not necessarily mean that every scalar expression runs in Rust. The node can still contain host-exact scalar upcalls or a whole-Calc Flink-generated evaluator.

Previously, the planner summary only reported operator substitution. A plan could therefore report that all operators were substituted natively while some functions still executed on the JVM, with no compile-time diagnostic explaining that placement.

What changed

• Record the final execution engine assignment for functions in admitted Calc and filter nodes.
• Log distinct function calls under native and jvm.
• Preserve the reason when host-exact evaluation or whole-Calc JVM evaluation is selected.
• Count Calc/filter nodes containing JVM functions in the always-on planner summary.
• Roll back provisional diagnostics when the surrounding native island is rejected.
• Show SQL functions, UDFs, and casts, while omitting arithmetic, comparison, and boolean operators.

With -Dstreamfusion.logFallbackReasons=true, function assignments are emitted at INFO; otherwise they remain available at DEBUG.

Example mixed execution:

NativeCalc functions: native=[CAST, CHAR_LENGTH], jvm=[JVM_ONLY],
reason=host-exact or scalar-UDF implementation selected

Example whole-Calc JVM execution:

NativeCalc functions: native=[], jvm=[IF],
reason=multiple fallible/JVM expressions require Flink's row-major error order

The planner summary now also reports the number of admitted Calc/filter nodes that contain JVM functions.

Testing

• Added coverage for fully native, mixed native/JVM, and whole-Calc JVM execution.
• Added coverage for multiple IF expressions requiring row-major JVM evaluation.
• Verified that casts remain visible while arithmetic and comparison operators are omitted.
• Targeted planner and generated-expression suite: 20 tests passed on Flink 2.2.1 / Java 17.

[ChaomingZhangCN]

@liuyongvs PTAL~

[liuyongvs]

LGTM +1