これは?

以下の記述が
packagingOptions {
  resources {
    excludes += "META-INF/rxjava.properties"
  }
}
これになりました。
fun Packaging.() {
  resources {
    excludes += "META-INF/rxjava.properties"
  }
}
なんだかおかしいです?
該当部分のコードを確認します。
    /**
     * Specifies options and rules that determine which files the Android plugin packages into your
     * APK.
     *
     * For more information about the properties you can configure in this block, see [Packaging].
     */
    @Deprecated("Renamed to packaging", replaceWith = ReplaceWith("packaging"))
    val packagingOptions: Packaging
    /**
     * Specifies options and rules that determine which files the Android plugin packages into your
     * APK.
     *
     * For more information about the properties you can configure in this block, see [Packaging].
     */
    @Deprecated("Renamed to packaging", replaceWith = ReplaceWith("packaging"))
    fun packagingOptions(action: Packaging.() -> Unit)
    /**
     * Specifies options and rules that determine which files the Android plugin packages into your
     * APK.
     *
     * For more information about the properties you can configure in this block, see [Packaging].
     */
    val packaging: Packaging
    /**
     * Specifies options and rules that determine which files the Android plugin packages into your
     * APK.
     *
     * For more information about the properties you can configure in this block, see [Packaging].
     */
    fun packaging(action: Packaging.() -> Unit)
こうですね。
packaging {
  resources {
    excludes += "META-INF/rxjava.properties"
  }
}
ついでに、短くしておきます。
packaging {
  resources.excludes += "META-INF/rxjava.properties"
}
これでOK。
👉 How to replace deprecated packagingOptions in Android Gradle build files - Stack Overflow 





