desktop_drop: restore Android compatibility with AGP < 9 hosts

[loucass]

Problem

desktop_drop 0.8.1 failed at configuration time on every app using AGP < 9 (localsend for example) with:

Build file '.../desktop_drop-0.8.1/android/build.gradle' line: 48
* What went wrong:
A problem occurred evaluating project ':desktop_drop'.
> Could not find method kotlin() for arguments [...] on project ':desktop_drop'

This affects all apps below Flutter 3.44 — they cannot simply move to AGP 9,
because Flutter itself only supports AGP 9 from 3.44+
(built-in Kotlin migration guide).
For those apps, the 0.8.0 changelog note ("must use AGP 9 or later") is unsatisfiable.

Root cause

android/build.gradle calls kotlin { compilerOptions {} } but never applies KGP:

Host	Who compiles Kotlin?	Unconditional kotlin{}	Conditional apply
AGP < 9	nobody → plugin must apply KGP itself	❌ kotlin() not found	✅ applies KGP itself
AGP ≥ 9	AGP built-in Kotlin	✅ works	✅ skips — hard error if applied

The example app (AGP 9.1) only ever exercised the second row, which is why this went
unnoticed. An alternative fix — raising the plugin's minimum to Flutter 3.44 — would
lock out apps on older stable versions; the conditional keeps every host working.

Fix

Implements the official guide section
"Support Flutter versions earlier than 3.44":

• apply kotlin-android only when host AGP major < 9
• bump bundled KGP 1.9.25 → 2.2.0, since the kotlin.compilerOptions {} DSL requires KGP ≥ 2.0

No Dart or Kotlin changes.

Verification

• AGP < 9 host: real app (LocalSend) builds its debug APK green on
  Flutter 3.41.9 · AGP 8.12.1 · Gradle 8.13 against this branch :
  run
  (✓ Built app-debug.apk; without the patch this same build fails at
  configuration time, before any compilation starts)
• AGP ≥ 9 host: example app builds green on AGP 9.1 · Gradle 9.3.1 · Flutter 3.47.1 :
  run

Could you tag a desktop_drop v0.8.2 after merge so downstream apps can pick this up? Thanks!

[ekuleshov]

With this change I'm getting the error below with Gradle 9.1.0 and Flutter 3.44.8.
desktop_drop 0.8.1 works

> Could not find method kotlin() for arguments [...] on project ':desktop_drop' of type org.gradle.api.Project.  

[loucass]

Thanks @ekuleshov for testing — that's a regression on the AGP 9 path.

You are on AGP 9.1 + Flutter 3.44.8 where built-in Kotlin should provide the kotlin {} extension, but my change bumped the bundled KGP to 2.2.0 and kept the direct kotlin {} DSL. On AGP 9 hosts that DSL can fail when KGP isn't applied (the extension is registered differently).

Fix: use the Flutter docs' recommended conditional pattern that works on both AGP < 9 and AGP 9+:

def agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.tokenize('.')[0] as int
if (agpMajor < 9) {
    apply plugin: 'kotlin-android'
}
project.extensions.configure(org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension) {
    compilerOptions { jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_1_8 }
}

And keep ext.kotlin_version compatible with the host (or keep 1.9.25 for now).

I'll open a follow-up PR with that fix. Could you confirm your app/android/settings.gradle AGP version and gradle-wrapper.properties Gradle version? Want to make sure we cover Gradle 9.1 correctly.

[ekuleshov]

id("org.jetbrains.kotlin.android") version "2.3.20" apply false

distributionUrl=https\://services.gradle.org/distributions/gradle-9.1.0-bin.zip

Also my app's jvmTarget is set to JvmTarget.JVM_17 for both java and kotlin code

[loucass]

Thanks for the details @ekuleshov Gradle 9.1 + KGP 2.3.20 + AGP 9.1 is exactly the combo that broke.

The issue was the direct kotlin {} DSL: on AGP 9 where built-in Kotlin is used, that extension isn't available as a direct method when KGP isn't applied.

Pushed a fix to branch fix/agp9-kotlin-configure that uses the robust form:

project.extensions.configure(org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension) {
    compilerOptions { jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17 }
}

This works whether the extension comes from KGP (AGP <9) or from AGP 9's built-in.

I'm working on the fix

[loucass]

@ekuleshov I have just opened #498