Cordova CLI project ignores build-extras after toolchain upgrade

Up until recently I have been using the following

Cordova Android 6.3.0
Gradle 4.9
- Node 8.9.2

to build my hybrid Android app which uses one custom - i.e. written by me - plugin. The plugin in turn has a number of external dependencies which I specify via the myapp/platforms/android/build-extras.gradle file which is listed below

ext.postBuildExtras = 
{
 android
 {
  dependencies
  {
   compile 'com.squareup.duktape:duktape-android:1.3.0'    
   compile 'net.zetetic:android-database-sqlcipher:3.5.9@aar'
   compile 'co.realtime:messaging-android:2.1.+'
   compile 'com.google.android.gms:play-services-location:15.0.1'
   compile 'com.android.installreferrer:installreferrer:1.0'
  } 
  defaultConfig
  {
   jackOptions {enabled true}
  }
  compileOptions 
  {
   sourceCompatibility JavaVersion.VERSION_1_8
   targetCompatibility JavaVersion.VERSION_1_8
  }
  allprojects
  {
   compileOptions
   {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
   }
  }
 }
}

I target Android SDK 26 with the minimum SDK level set at 23. My Cordova config.xml file is shown below

<?xml version='1.0' encoding='utf-8'?>
<widget android-versionCode="1190" android-versionName="Etoile-2" 
 id="my.app.id" version="1.1.9" xmlns="http://www.w3.org/ns/widgets" 
 xmlns:cdv="http://cordova.apache.org/ns/1.0">
 <name>My App</name>
 <description>My App</description>
 <author email="someone@gmail.com" href="https://example.org">My Name. 
 </author>
 <content src="index.html" />
 <access origin="*" />
 <icon platform="android" qualifier="mdpi" src="res/mdpi.png" />
 <icon platform="android" qualifier="hdpi" src="res/hdpi.png" />
 <icon platform="android" qualifier="xhdpi" src="res/xhdpi.png" />
 <icon platform="android" qualifier="xxdpi" src="res/xxdpi.png" />
 <icon platform="android" qualifier="xxxdpi" src="res/xxxdpi.png" />
 <allow-intent href="http://*/*" />
 <allow-intent href="https://*/*" />
 <allow-intent href="tel:*" />
 <allow-intent href="sms:*" />
 <allow-intent href="mailto:*" />
 <allow-intent href="geo:*" />
 <platform name="android">
     <allow-intent href="market:*" />
     <FrameLayout android:focusable="true" 
      android:focusableInTouchMode="true" 
      android:layout_height="match_parent" 
      android:layout_width="match_parent" 
      xmlns:android="http://schemas.android.com/apk/res/android">
    </FrameLayout>
    <preference name="android-minSdkVersion" value="23" />
    <preference name="android-targetSdkVersion" value="26" />
 </platform>
 <preference name="Orientation" value="portrait" />
 <plugin name="ext.org.plugin" spec="path:\to\my\plugin" />
 <engine name="android" spec="^7.0.0" />
</widget>

I am in the process of provisioning a more modern Windows PC to do my Android builds. In the process I have upgraded to

Cordova Android 7.0.0
Gradle 4.10.0 (installed via Scoop)
Node 10.10.0

I went through the process of reconstructing the entire project step-by-step

Create a new Cordova CLI project cordova create myapp ext.example.myproj MyApp
Add the Android platform cordova platform add android which adds Cordova Android 7.0.0
Build this dummy app cordova build android --debug: working
Replace the default Cordova config.xml with my version (shown above) minus the reference to my custom plugin
Build again - still working
Copy across my original build-extras.gradle file to myapp/platforms/android
Build again - still working
Add my custom plugin cordova plugin add 'path:\to\my\plugin
Issue a cordova clean followed by cordova build android which results in errors along the lines of

:app:compileDebugJavaWithJavac path:\to\my\app\platforms\android\app\src\main\java\ext\example\plugin\BCTrailer.java:4: error: package net.sqlcipher does not exist import net.sqlcipher.Cursor;

which appears to imply that the contents of my build-extras.gradle file were not used during the build. I deliberately corrupted that file by leaving out a brace to make the XML invalid. If the file were being read I had expected that Gradle would complain. Instead it just goes ahead and issues the same errors such as package net.sqlcipher does not exist etc.

I have noted talk of compile being deprecated in dependencies in favor of a whole new clutch of instructions such as implementation and api. I tried replacing compile with implementation in my own build-extras.gradle file but to no avail.

Clearly, I am doing something wrong here and it has to do with the changes in Gradle.

Solution

Whilst I still do not understand the root cause of the problems I ran into during my attempt at upgrading the Android APK build toolchain I now have a solution which I am sharing here for the benefit of others who find this thread.

With Cordova Android 7.0.0 (as opposed to 6.3.1 which I was using previously) build-extras.gradle in the myapp/platforms/android folder is being ignored.
It was in any case incorrect to start declaring plugin dependencies via a build-extras file in the APK project itself.
Although this had always worked for me prior to this toolchain upgrade I had found it rather strange that dependencies declared in a build-extras.gradle **ext.postBuildExtras** were working to fork in external dependencies in a plugin which one would assume had been built in to the app by that point.
I tried switching my dependencies declaration to a build.gradle file in the actual plugin. However, this did not change the outcome - the dependencies did not make it into the build with the result that various import path.to.external.dependency declarations in Java units in the plugin threw errors.
I removed the build.gradle file and declared the dependencies via a series of <framework src='path/to/dependency' /> dependency statements in the plugin.xml file and Bingo! - it all worked.

As a side note - with Cordova Android 7 and anything higher than Node 9.0 you no longer need to use the, now deprecated, Jack compiler or do anything else to persuade Gradle/Android/Cordova to use Java 8. I am now no longer using a build-extras.gradle file in my app or a build.gradle file in my plugin.