Fangchen Li created SPARK-57596:
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Summary: De-reflect ScalaReflection.findConstructor's
companion-apply fallback
Key: SPARK-57596
URL: https://issues.apache.org/jira/browse/SPARK-57596
Project: Spark
Issue Type: Sub-task
Components: Spark Core, SQL
Affects Versions: 4.3.0
Reporter: Fangchen Li
ScalaReflection.findConstructor resolves how to instantiate a type. It first
looks for a matching constructor via Java reflection (ConstructorUtils); only
if none is accessible does it fall back to a companion-object `apply` method,
which it finds and invokes via scala.reflect (the runtime universe —
mirror.staticClass(...), universe.TermName("apply")).
That fallback is the only scala.reflect.runtime use left among the object's
codegen utilities. A Scala companion is just a JVM class with a static MODULE$
and an `apply` method, so the same lookup is reachable by ordinary Java
reflection — no runtime universe needed.
Proposed: reimplement the fallback with Java reflection. Behavior-preserving on
2.13.
Reference + test (resolves a companion `apply` from a Scala 3 process; confirms
a matching constructor still takes precedence):
https://github.com/bearing-research/ProtoCatalyst (spark-reflection-patch/,
FindConstructorFallbackSpec)
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