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The Checker Framework enhances Java's type system to make it more powerful and useful. This lets software developers detect and prevent errors in their Java programs. The Checker Framework includes compiler plug-ins ("checkers") that find bugs or verify their absence. It also permits you to write your own compiler plug-ins.

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package org.checkerframework.framework.util.element;

import static com.sun.tools.javac.code.TargetType.CAST;
import static com.sun.tools.javac.code.TargetType.CONSTRUCTOR_INVOCATION_TYPE_ARGUMENT;
import static com.sun.tools.javac.code.TargetType.CONSTRUCTOR_REFERENCE;
import static com.sun.tools.javac.code.TargetType.CONSTRUCTOR_REFERENCE_TYPE_ARGUMENT;
import static com.sun.tools.javac.code.TargetType.EXCEPTION_PARAMETER;
import static com.sun.tools.javac.code.TargetType.FIELD;
import static com.sun.tools.javac.code.TargetType.INSTANCEOF;
import static com.sun.tools.javac.code.TargetType.LOCAL_VARIABLE;
import static com.sun.tools.javac.code.TargetType.METHOD_INVOCATION_TYPE_ARGUMENT;
import static com.sun.tools.javac.code.TargetType.METHOD_REFERENCE;
import static com.sun.tools.javac.code.TargetType.METHOD_REFERENCE_TYPE_ARGUMENT;
import static com.sun.tools.javac.code.TargetType.NEW;
import static com.sun.tools.javac.code.TargetType.RESOURCE_VARIABLE;
import static org.checkerframework.framework.util.element.ElementAnnotationUtil.addAnnotationsFromElement;
import static org.checkerframework.framework.util.element.ElementAnnotationUtil.annotateViaTypeAnnoPosition;
import static org.checkerframework.framework.util.element.ElementAnnotationUtil.contains;

import com.sun.tools.javac.code.Attribute;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.TargetType;
import java.util.List;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.type.TypeKind;
import org.checkerframework.framework.type.AnnotatedTypeMirror;
import org.checkerframework.javacutil.ErrorReporter;

/**
 * Applies annotations to variable declaration (providing they are not the use of a TYPE_PARAMETER).
 */
public class VariableApplier extends TargetedElementAnnotationApplier {

    public static void apply(final AnnotatedTypeMirror type, final Element element) {
        new VariableApplier(type, element).extractAndApply();
    }

    private static final ElementKind[] acceptedKinds = {
        ElementKind.LOCAL_VARIABLE, ElementKind.RESOURCE_VARIABLE, ElementKind.EXCEPTION_PARAMETER
    };

    /** @return true if this is a variable declaration including fields an enum constants */
    public static boolean accepts(final AnnotatedTypeMirror typeMirror, final Element element) {
        return contains(element.getKind(), acceptedKinds) || element.getKind().isField();
    }

    private final Symbol.VarSymbol varSymbol;

    VariableApplier(final AnnotatedTypeMirror type, final Element element) {
        super(type, element);
        varSymbol = (Symbol.VarSymbol) element;

        if (type.getKind() == TypeKind.UNION
                && element.getKind() != ElementKind.EXCEPTION_PARAMETER) {
            ErrorReporter.errorAbort(
                    "Union types only allowed for exception parameters! "
                            + "Type: "
                            + type
                            + " for element: "
                            + element);
        }
        // TODO: need a way to split the union types into the right alternative
        // to use for the annotation. The exception_index is probably what we
        // need to look at, but it might not be set at this point.
    }

    @Override
    protected TargetType[] annotatedTargets() {
        return new TargetType[] {LOCAL_VARIABLE, RESOURCE_VARIABLE, EXCEPTION_PARAMETER, FIELD};
    }

    @Override
    protected TargetType[] validTargets() {
        return new TargetType[] {
            NEW,
            CAST,
            INSTANCEOF,
            METHOD_INVOCATION_TYPE_ARGUMENT,
            CONSTRUCTOR_INVOCATION_TYPE_ARGUMENT,
            METHOD_REFERENCE,
            CONSTRUCTOR_REFERENCE,
            METHOD_REFERENCE_TYPE_ARGUMENT,
            CONSTRUCTOR_REFERENCE_TYPE_ARGUMENT
        };
    }

    @Override
    protected Iterable getRawTypeAttributes() {
        return varSymbol.getRawTypeAttributes();
    }

    @Override
    protected boolean isAccepted() {
        return accepts(type, element);
    }

    @Override
    protected void handleTargeted(final List targeted) {
        annotateViaTypeAnnoPosition(type, targeted);
    }

    @Override
    public void extractAndApply() {
        // Add declaration annotations to the local variable type
        addAnnotationsFromElement(type, varSymbol.getAnnotationMirrors());
        super.extractAndApply();
    }
}