Crash if the shade list is accessed during the build process.

    /**

     * Returns a read-only view in to the current shade list, i.e. the list of notifications that

     * are currently present in the shade. If this method is called during pipeline execution it

     * will return the current state of the list, which will likely be only partially-generated.

     * are currently present in the shade.

     * @throws IllegalStateException if called during pipeline execution.

     */

    val shadeList: List<ListEntry>

        get() = mShadeListBuilder.shadeList

    /**

     * Constructs a flattened representation of the notification tree, where each group will have

     * the summary (if present) followed by the children.

     * @throws IllegalStateException if called during pipeline execution.

     */

    fun getFlatShadeList(): List<NotificationEntry> = shadeList.flatMap { entry ->

        when (entry) {

            is NotificationEntry -> sequenceOf(entry)

            is GroupEntry -> (entry.summary?.let { sequenceOf(it) }.orEmpty() +

                    entry.children)

            is GroupEntry -> sequenceOf(entry.summary).filterNotNull() + entry.children

            else -> throw RuntimeException("Unexpected entry $entry")

        }

    }

    /**

     * Returns the number of notifications currently shown in the shade. This includes all

     * children and summary notifications. If this method is called during pipeline execution it

     * will return the number of notifications in its current state, which will likely be only

     * partially-generated.

     * children and summary notifications.

     * @throws IllegalStateException if called during pipeline execution.

     */

    fun getShadeListCount(): Int = shadeList.sumOf { entry ->

        // include the summary in the count

    List<ListEntry> getShadeList() {

        Assert.isMainThread();

        // NOTE: Accessing this method when the pipeline is running is generally going to provide

        //  incorrect results, and indicates a poorly behaved component of the pipeline.

        mPipelineState.requireState(STATE_IDLE);

        return mReadOnlyNotifList;

    }