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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.dataflow.util;

import com.sun.source.tree.MethodTree;

import org.checkerframework.dataflow.qual.Deterministic;
import org.checkerframework.dataflow.qual.Pure;
import org.checkerframework.dataflow.qual.SideEffectFree;
import org.checkerframework.javacutil.AnnotationProvider;
import org.checkerframework.javacutil.ElementUtils;
import org.checkerframework.javacutil.TreeUtils;

import java.util.EnumSet;

import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.ExecutableElement;

/**
 * A utility class for working with the {@link SideEffectFree}, {@link Deterministic}, and {@link
 * Pure} annotations.
 *
 * @see SideEffectFree
 * @see Deterministic
 * @see Pure
 */
public class PurityUtils {

    /** Do not instantiate. */
    private PurityUtils() {
        throw new Error("Do not instantiate PurityUtils.");
    }

    /** Represents a method that is both deterministic and side-effect free. */
    private static final EnumSet detAndSeFree =
            EnumSet.of(Pure.Kind.DETERMINISTIC, Pure.Kind.SIDE_EFFECT_FREE);

    /**
     * Does the method {@code methodTree} have any purity annotation?
     *
     * @param provider how to get annotations
     * @param methodTree a method to test
     * @return whether the method has any purity annotations
     */
    public static boolean hasPurityAnnotation(AnnotationProvider provider, MethodTree methodTree) {
        return !getPurityKinds(provider, methodTree).isEmpty();
    }

    /**
     * Does the method {@code methodElement} have any purity annotation?
     *
     * @param provider how to get annotations
     * @param methodElement a method to test
     * @return whether the method has any purity annotations
     */
    public static boolean hasPurityAnnotation(
            AnnotationProvider provider, ExecutableElement methodElement) {
        return !getPurityKinds(provider, methodElement).isEmpty();
    }

    /**
     * Is the method {@code methodTree} deterministic?
     *
     * @param provider how to get annotations
     * @param methodTree a method to test
     * @return whether the method is deterministic
     */
    public static boolean isDeterministic(AnnotationProvider provider, MethodTree methodTree) {
        ExecutableElement methodElement = TreeUtils.elementFromDeclaration(methodTree);
        return isDeterministic(provider, methodElement);
    }

    /**
     * Is the method {@code methodElement} deterministic?
     *
     * @param provider how to get annotations
     * @param methodElement a method to test
     * @return whether the method is deterministic
     */
    public static boolean isDeterministic(
            AnnotationProvider provider, ExecutableElement methodElement) {
        EnumSet kinds = getPurityKinds(provider, methodElement);
        return kinds.contains(Pure.Kind.DETERMINISTIC);
    }

    /**
     * Is the method {@code methodTree} side-effect-free?
     *
     * This method does not use, and has different semantics than, {@link
     * AnnotationProvider#isSideEffectFree}. This method is concerned only with standard purity
     * annotations.
     *
     * @param provider how to get annotations
     * @param methodTree a method to test
     * @return whether the method is side-effect-free
     * @deprecated use {@link AnnotationProvider#isSideEffectFree}
     */
    @Deprecated // 2022-09-27
    public static boolean isSideEffectFree(AnnotationProvider provider, MethodTree methodTree) {
        ExecutableElement methodElement = TreeUtils.elementFromDeclaration(methodTree);
        return isSideEffectFree(provider, methodElement);
    }

    /**
     * Is the method {@code methodElement} side-effect-free?
     *
     * This method does not use, and has different semantics than, {@link
     * AnnotationProvider#isSideEffectFree}. This method is concerned only with standard purity
     * annotations.
     *
     * @param provider how to get annotations
     * @param methodElement a method to test
     * @return whether the method is side-effect-free
     */
    public static boolean isSideEffectFree(
            AnnotationProvider provider, ExecutableElement methodElement) {
        EnumSet kinds = getPurityKinds(provider, methodElement);
        return kinds.contains(Pure.Kind.SIDE_EFFECT_FREE);
    }

    /**
     * Returns the purity annotations on the method {@code methodTree}.
     *
     * @param provider how to get annotations. Its {@link AnnotationProvider#isSideEffectFree} and
     *     {@link AnnotationProvider#isDeterministic} methods are not used.
     * @param methodTree a method to test
     * @return the types of purity of the method {@code methodTree}
     */
    public static EnumSet getPurityKinds(
            AnnotationProvider provider, MethodTree methodTree) {
        ExecutableElement methodElement = TreeUtils.elementFromDeclaration(methodTree);
        return getPurityKinds(provider, methodElement);
    }

    /**
     * Returns the purity annotations on the method {@code methodElement}.
     *
     * @param provider how to get annotations. Its {@link AnnotationProvider#isSideEffectFree} and
     *     {@link AnnotationProvider#isDeterministic} methods are not used.
     * @param methodElement a method to test
     * @return the types of purity of the method {@code methodElement}
     */
    public static EnumSet getPurityKinds(
            AnnotationProvider provider, ExecutableElement methodElement) {
        // Special case for record accessors
        if (ElementUtils.isRecordAccessor(methodElement)
                && ElementUtils.isAutoGeneratedRecordMember(methodElement)) {
            return detAndSeFree;
        }

        AnnotationMirror pureAnnotation = provider.getDeclAnnotation(methodElement, Pure.class);
        AnnotationMirror sefAnnotation =
                provider.getDeclAnnotation(methodElement, SideEffectFree.class);
        AnnotationMirror detAnnotation =
                provider.getDeclAnnotation(methodElement, Deterministic.class);

        if (pureAnnotation != null) {
            return detAndSeFree;
        }
        EnumSet result = EnumSet.noneOf(Pure.Kind.class);
        if (sefAnnotation != null) {
            result.add(Pure.Kind.SIDE_EFFECT_FREE);
        }
        if (detAnnotation != null) {
            result.add(Pure.Kind.DETERMINISTIC);
        }
        return result;
    }
}