Add Delegation Checker

[jyoo980]

No description provided.

[smillst]

This needs to extend SourceChecker.

[Copilot]

Pull Request Overview

This PR implements a new Delegation Checker that enforces syntactic checks for the @Delegate annotation. The checker validates that classes using delegation follow specific patterns: having at most one delegate field, properly delegating method calls, and overriding required methods.

• Adds a complete delegation checker framework with visitor, type factory, and checker classes
• Implements comprehensive test suite covering various delegation scenarios
• Includes proper error message handling and validation logic

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
DelegationChecker.java	Main checker class that extends BaseTypeChecker
DelegationVisitor.java	Core visitor implementing delegation validation logic
DelegationAnnotatedTypeFactory.java	Type factory for handling delegation annotations
Delegate.java	Annotation marking fields as delegates
DelegatorMustOverride.java	Annotation for methods that must be overridden by delegating classes
messages.properties	Error message definitions for the delegation checker
DelegationTest.java	JUnit test runner for the delegation checker
Various test files	Test cases covering different delegation scenarios
AnnotatedTypes.java	Minor comment improvements for clarity

Comments suppressed due to low confidence (1)

framework/src/main/java/org/checkerframework/common/delegation/DelegationVisitor.java:42

• [nitpick] The constant name MAX_NUM_DELEGATE_FIELDS should follow Java naming conventions and be more descriptive. Consider renaming it to MAX_DELEGATE_FIELDS_PER_CLASS.

  private final int MAX_NUM_DELEGATE_FIELDS = 1;

[Copilot]

The TODO comment identifies a significant limitation: the current implementation doesn't handle method overloading correctly. Consider using ExecutableElement comparison or method signatures instead of just names.

Suggested change

	Set<Name> overriddenMethods =
	getOverriddenMethods(tree).stream()
	.map(ExecutableElement::getSimpleName)
	.collect(Collectors.toSet());
	Set<ExecutableElement> methodsDeclaredInSuperClass =
	new HashSet<>(ElementFilter.methodsIn(superClassMirror.asElement().getEnclosedElements()));
	Set<Name> methodsThatMustBeOverriden =
	methodsDeclaredInSuperClass.stream()
	.filter(e -> atypeFactory.getDeclAnnotation(e, DelegatorMustOverride.class) != null)
	.map(ExecutableElement::getSimpleName)
	.collect(Collectors.toSet());
	// TODO: comparing a set of names isn't ideal, what about overloading?
	Set<String> overriddenMethods =
	getOverriddenMethods(tree).stream()
	.map(ExecutableElement::toString)
	.collect(Collectors.toSet());
	Set<ExecutableElement> methodsDeclaredInSuperClass =
	new HashSet<>(ElementFilter.methodsIn(superClassMirror.asElement().getEnclosedElements()));
	Set<String> methodsThatMustBeOverriden =
	methodsDeclaredInSuperClass.stream()
	.filter(e -> atypeFactory.getDeclAnnotation(e, DelegatorMustOverride.class) != null)
	.map(ExecutableElement::toString)
	.collect(Collectors.toSet());
	// Compare full method signatures to handle overloading