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Y20240722-1000

Y20240722-1000: [23] JEP 482: Flexible Constructor Bodies (Second Preview) (#2685)
@stephan-herrmann stephan-herrmann tagged this 15 Jul 22:24 
Preparation
+ renamed the feature from "Statements before Super" to 
  "Flexible Constructor Bodies"
+ move the main flag, let ClassScope manage early construction contexts

Implement updates for JEP 482:
+ change wording towards "early construction context"
+ determine early-ctor-ctx based on target class
+ fine tuning:
  - where should enclosing types be considered?
  - search for enclosings first
    but also consider their supers in a second round
+ reduce # mechanisms for detecting early construction context
+ allow assignment to fields of uninitialized instance
+ differentiate new errors:
  - FieldReadInEarlyConstructionContext
  - ThisInEarlyConstructionContext
  - AllocationInEarlyConstructionContext
  - MessageSendInEarlyConstructionContext
  - DuplicateExplicitConstructorCall
  - ConstructorCallNotAllowedHere
  - SuperFieldAssignInEarlyConstructionContext
  - AssignFieldWithInitializerInEarlyConstructionContext
+ generation of synth args and fields for enclosing instances
  - such synthetics allow to skip over unavailable enclosing instances 
    towards outer instances that are available

Documentation of key strategies as javadoc / code comments:
+ enablement: JavaFeature.FLEXIBLE_CONSTRUCTOR_BODIES
  2-step strategy
  - does compliance generally allow the use of this feature?
    already at this level we may suggest to enable the feature
  - is the preview feature enabled?
+ detection / analysis: ClassScope.insideEarlyConstructionContext
  - describes the combination of structural and temporary contexts
+ explicit vs implicit constructor calls: CD.resolveStatements()
  - code comment describing updated contract of CD.constructorCall
+ code gen: TypeDeclaration.manageEnclosingInstanceAccessIfNecessary()
  - code comment describing the strategy to generate synth args & fields
    for various outer classes, which orchestrates code generation

Fixes https://github.com/eclipse-jdt/eclipse.jdt.core/issues/2472
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