private static final SessionData.Key<ProjectIndex> PROJECT_INDEX = SessionData.key(ProjectIndex.class);

    @SuppressWarnings({"unchecked", "rawtypes"})
    private static final SessionData.Key<Map<MavenProject, OwnerReentrantLock>> PROJECT_LOCKS =
            (SessionData.Key) SessionData.key(Map.class, ProjectLock.class);

    private final BuildPluginManager pluginManager;

        return groupId + ":" + artifactId;
    }

    public static String key(Artifact artifact) {
        return key(artifact.getGroupId(), artifact.getArtifactId(), artifact.getVersion());
    }

    public static String key(String groupId, String artifactId, String version) {
        notBlank(groupId, "groupId can neither be null, empty nor blank");

                for (Map.Entry<String, String> entry : System.getenv().entrySet()) {
                    String key = "env."
                            + (caseSensitive ? entry.getKey() : entry.getKey().toUpperCase(Locale.ENGLISH));
                    tmp.setProperty(key, entry.getValue());
                }
                envVars = tmp;
            }

            props.putAll(envVars);
        }
    }

    private final int rank;

    private final String key;

    private static Map<String, ArtifactStatus> map;

    private ArtifactStatus(String key, int rank) {
        this.rank = rank;
        this.key = key;

        if (map == null) {
            map = new HashMap<>();
        }
        map.put(key, this);
    }

    public static ArtifactStatus valueOf(String status) {

                        String key = plugin.getKey();
                        managedVersions.computeIfAbsent(key, k -> plugin.getVersion());
                    }
                }
            }
        }

        for (String key : versions.keySet()) {
            if (versions.get(key) == null && managedVersions.get(key) == null) {

        Key key = new CacheKey(
                project,
                project.getRemoteProjectRepositories(),
                scopesToCollect,
                scopesToResolve,
                aggregating,
                session);
        return keys.computeIfAbsent(key, k -> k);
    }

    @Override
    public CacheRecord get(Key key) throws LifecycleExecutionException {

    }

    public CacheRecord get(Key key) throws PluginResolutionException {
        CacheRecord cacheRecord = cache.get(key);

        if (cacheRecord != null && cacheRecord.getException() != null) {
            throw cacheRecord.getException();
        }

        return cacheRecord;
    }

    public CacheRecord put(Key key, List<Artifact> pluginArtifacts) {

                    Object key = getPluginExecutionKey().apply(element);
                    merged.put(key, element);
                }

                for (PluginExecution element : src) {
                    Object key = getPluginExecutionKey().apply(element);
                    PluginExecution existing = merged.get(key);
                    if (existing != null) {

    }

    public <T> void seed(Class<T> clazz, Provider<T> value) {
        getScopeState().seeded.put(Key.get(clazz), value);
    }

    public <T> void seed(Class<T> clazz, final T value) {
        getScopeState().seeded.put(Key.get(clazz), Providers.of(value));
    }

    public <T> Provider<T> scope(final Key<T> key, final Provider<T> unscoped) {
        return () -> {
            LinkedList<ScopeState> stack = values.get();

        String key = "m2.name";
        String checkValue = "value";

        MavenProject project = createDefaultProject();
        project.getModel().getProperties().setProperty(key, checkValue);

        ExpressionEvaluator ee = createExpressionEvaluator(project, new Properties());

        Object value = ee.evaluate("${" + key + "}");

        assertEquals(checkValue, value);
    }