*
     * The operation might be called regularly, so the [getFilePackageName] should work fast and avoid building the whole file text.
     *
     * It should be equal to the package name specified in the [buildFileText].
     *
     * @see KaResolveExtensionFile
     */
    public abstract fun getFilePackageName(): FqName

    /**

    private val topLevelCallableNames: Set<Name> = topLevelCallableNames.mapTo(mutableSetOf()) { Name.identifier(it) }
    override fun getFileName(): String = fileName
    override fun getFilePackageName(): FqName = packageName
    override fun getTopLevelClassifierNames(): Set<Name> = topLevelClassifiersNames
    override fun getTopLevelCallableNames(): Set<Name> = topLevelCallableNames

     *
     * The returned package set should be a strict set of all file packages,
     * so `for-all pckg: pckg in getContainedPackages() <=> exists file: file in getKtFiles() && file.getFilePackageName() == pckg`
     *
     * @see KaResolveExtension
     */
    public abstract fun getContainedPackages(): Set<FqName>

    /**