[BUG] CompletionParser invokes Lombok annotation handlers with partial AST node (CompletionOnFieldType) causing ClassCastException cascade

[clementb49]

Environment

• Jackson: 3.1.4
• JDT Language Server: 1.59.0-SNAPSHOT (OSGi 1.59.0.202606241329, commit ab9b695)
• Lombok: 1.18.46
• JDK: 21.0.11 (Eclipse Adoptium)
• VSCode Java extension (redhat.java)
• OS: Linux x86_64

Description

When @Builder and @Jacksonized are combined on an inner class of a
sealed interface, JDT's CompletionParser invokes Lombok annotation
handlers via visitAnnotationOnField with a CompletionOnFieldType node
instead of a TypeDeclaration node. This causes a ClassCastException
in lombok.eclipse.handlers.HandleValue which cascades into false
compilation errors reported by JDT on the affected file.

The CompletionParser builds a partial AST when resolving quick fix
proposals (UnresolvedElementsSubProcessor → CompletionEngine). In
this context, field type nodes are represented as CompletionOnFieldType
instances (which extend TypeReference) rather than TypeDeclaration.
Lombok's TransformEclipseAST is invoked on this partial AST via
transform_swapped, and its AnnotationVisitor calls
visitAnnotationOnField with these partial nodes, which Lombok handlers
do not expect.

This has been reported to the Lombok project as issue
projectlombok/lombok#4051, where a fix via
instanceof guard in HandleValue is proposed. However the root question
is whether the CompletionParser should be invoking Lombok's transform
on a partial AST at all, or whether JDT should guard against passing
incomplete AST nodes to annotation processors in this path.

Impact

• HandleValue crashes repeatedly on every autocompletion and quick fix
  attempt on the affected file
• JDT reports false compilation errors (cannot be resolved to a type)
  on Jackson annotations in the affected class, cascading from the crash
• The VSCode debug launch is blocked because JDT considers the project
  as having compilation errors
• mvn compile succeeds without errors

Stack trace

!ENTRY org.eclipse.jdt.core 4 0 2026-06-26 13:56:59.246
!MESSAGE Lombok annotation handler class lombok.eclipse.handlers.HandleValue failed
!STACK 0
java.lang.ClassCastException: class org.eclipse.jdt.internal.codeassist.complete.CompletionOnFieldType
cannot be cast to class org.eclipse.jdt.internal.compiler.ast.TypeDeclaration
(org.eclipse.jdt.internal.codeassist.complete.CompletionOnFieldType is in unnamed module of loader
org.eclipse.osgi.internal.loader.EquinoxClassLoader @222140f1;
org.eclipse.jdt.internal.compiler.ast.TypeDeclaration is in unnamed module of loader
org.eclipse.osgi.internal.loader.EquinoxClassLoader @4d4271d6)
    at lombok.eclipse.handlers.HandleValue.handle(HandleValue.java:66)
    at lombok.eclipse.HandlerLibrary$AnnotationHandlerContainer.handle(HandlerLibrary.java:106)
    at lombok.eclipse.HandlerLibrary.handleAnnotation(HandlerLibrary.java:237)
    at lombok.eclipse.TransformEclipseAST$AnnotationVisitor.visitAnnotationOnField(TransformEclipseAST.java:249)
    at lombok.eclipse.EclipseNode.traverse(EclipseNode.java:110)
    at lombok.eclipse.EclipseAST.traverseChildren(EclipseAST.java:232)
    at lombok.eclipse.EclipseNode.traverse(EclipseNode.java:79)
    at lombok.eclipse.EclipseAST.traverseChildren(EclipseAST.java:232)
    at lombok.eclipse.EclipseNode.traverse(EclipseNode.java:74)
    at lombok.eclipse.EclipseAST.traverseChildren(EclipseAST.java:232)
    at lombok.eclipse.EclipseNode.traverse(EclipseNode.java:69)
    at lombok.eclipse.EclipseAST.traverse(EclipseAST.java:225)
    at lombok.eclipse.TransformEclipseAST.go(TransformEclipseAST.java:226)
    at lombok.eclipse.TransformEclipseAST.transform(TransformEclipseAST.java:187)
    at lombok.eclipse.TransformEclipseAST.transform_swapped(TransformEclipseAST.java:104)
    at org.eclipse.jdt.internal.compiler.parser.Parser.endParse(Parser.java:10537)
    at org.eclipse.jdt.internal.codeassist.complete.CompletionParser.endParse(CompletionParser.java:6302)
    at org.eclipse.jdt.internal.compiler.parser.Parser.parse(Parser.java:11729)
    at org.eclipse.jdt.internal.codeassist.CompletionEngine.complete(CompletionEngine.java:1996)
    at org.eclipse.jdt.internal.core.Openable.codeComplete(Openable.java:139)
    at org.eclipse.jdt.ls.core.internal.corrections.proposals.UnresolvedElementsSubProcessor
         .collectTypeProposals(UnresolvedElementsSubProcessor.java:330)
    at org.eclipse.jdt.ls.core.internal.handlers.CodeActionHandler
         .getCodeActionCommands(CodeActionHandler.java:204)

Minimal reproducer

import lombok.Builder;
import lombok.extern.jackson.Jacksonized;

public sealed interface MyInterface permits MyInterface.MyInnerDTO {

    @Builder
    @Jacksonized
    class MyInnerDTO implements MyInterface {
        String field;
    }
}

Open the file in VSCode and trigger autocompletion or a quick fix.
The crash occurs immediately and repeats on every completion attempt.

Question for JDT team

Should CompletionParser / CompletionEngine be invoking
TransformEclipseAST.transform_swapped (the Lombok AST transform entry
point) on a partial AST? If the answer is no, a guard in
CompletionParser.endParse before invoking any registered AST transforms
would prevent this class of issue generically, rather than requiring every
Lombok handler to individually guard against partial AST nodes.

Related

• Lombok issue: [BUG] HandleValue crashes with ClassCastException on CompletionOnFieldType when @Jacksonized and @Builder are combined on inner class of sealed interface projectlombok/lombok#4051
• Similar JDT/Lombok incompatibility resolved in
  [BUG] Internal package changes in ECJ will break Lombok. projectlombok/lombok#3564
  (originally filed on eclipse-jdtls)