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Refactoring: Companion Class/Object Support

Overview

Refactored lazy val detection and patching to handle companion class/object pairs where OFFSET fields may be split across the companion class while lazy val implementation lives in the companion object.

Key Structural Changes

1. LazyValDetector API Change

  • Before: detect(classInfo: ClassInfo)
  • After: detect(classInfo: ClassInfo, companionClassInfo: Option[ClassInfo])
  • Now accepts optional companion class for cross-class field analysis

2. New OffsetFieldLocation Enum

enum OffsetFieldLocation:
  case InSameClass        // OFFSET in same class as lazy val
  case InCompanionClass   // OFFSET in companion class, lazy val in object
  case NoOffsetField      // No OFFSET (3.8+ VarHandle)

Tracks where OFFSET fields are located in companion scenarios.

3. Enhanced Offset Mapping

  • buildOffsetMapping now searches <clinit> in both current class and companion class
  • Extracts helper parseClinitMethod for reuse across multiple classes
  • Maps OFFSET fields regardless of which class contains them

4. Field Search Across Classes

  • findOffsetFieldForStorage returns tuple: (Option[FieldInfo], OffsetFieldLocation)
  • Searches current class first, then companion class
  • findBitmapFieldForStorage receives combined field list from both classes

5. LazyValInfo Model Update

final case class LazyValInfo(
  // ... existing fields ...
  offsetFieldLocation: OffsetFieldLocation,  // NEW
  // ...
)

6. BytecodePatcher Redesign

  • Before: patch(bytes: Array[Byte])
  • After: patch(group: ClassfileGroup)
  • Now works with ClassfileGroup (Single | CompanionPair)
  • Returns PatchedSingle or PatchedPair based on input

7. PatchResult Variants

sealed trait PatchResult
case class PatchedSingle(name: String, bytes: Array[Byte])
case class PatchedPair(
  companionObjectName: String,
  className: String,
  companionObjectBytes: Array[Byte],
  classBytes: Array[Byte]
)

8. Companion Class Patching (3.3-3.7)

  • New patchCompanionClass33x_37x helper
  • Removes OFFSET$_m_N fields from companion class
  • Removes method from companion class
  • Returns both patched object and class bytes

Problem Addressed

Companion objects with lazy vals in Scala 3.x store:

  • Lazy val implementation (storage field, accessor, initialization) in companion object Foo$
  • OFFSET field (for memory offset calculation) in companion class Foo
  • initialization (calculates OFFSET) in companion class Foo

Previous implementation only analyzed single classfiles and couldn't detect this split configuration.

Impact

  • Detection now correctly identifies lazy vals in companion object scenarios across all Scala 3.x versions
  • Patching can transform both companion object and class when needed (3.3-3.7)
  • Maintains backward compatibility with standalone objects/classes