fix: use builtInKotlin property to conditionally apply KGP

[loucass]

Problem

desktop_drop 0.8.2 and 0.8.3 failed to compile Kotlin on one AGP version or the other:

• AGP 8: kotlin() not found — no Kotlin extension without KGP applied
• AGP 9.1 (Flutter 3.44, builtInKotlin=false): kotlin() not found — AGP 9 doesn't register the extension for plugin subprojects; tasks.withType(KotlinCompile) found no tasks to configure

Every conditional approach (if/else on agpMajor, tasks.withType) broke one side because on Flutter 3.44, builtInKotlin=false means AGP 9 does NOT automatically provide Kotlin for plugins. The plugin must apply KGP itself.

Solution

Branch on the android.builtInKotlin Gradle property instead of the AGP version number:

• builtInKotlin=false → apply KGP + use kotlinOptions (AGP 8, or AGP 9 with Flutter <3.47)
• builtInKotlin=true → skip KGP + use compilerOptions (AGP 9 with Flutter 3.47+)

This is more precise than checking agpMajor because it directly reads whether AGP provides Kotlin built-in, rather than guessing from the version number. It avoids the KGP non-compliance warning on hosts where it's not needed.

Changes

• android/build.gradle: Read android.builtInKotlin property. Conditionally apply kotlin-android and use the appropriate DSL (kotlinOptions vs compilerOptions).

Testing

Both AGP paths verified:

Host	Config	builtInKotlin	Result
AGP 8.12	Flutter 3.47, Gradle 8.14	false	✅ Applies KGP, kotlinOptions
AGP 9.1	Flutter 3.44+, Gradle 9.1+, KGP 2.3.20	false	✅ Applies KGP, kotlinOptions
AGP 9	Flutter 3.47+, builtInKotlin=true	true	✅ Skips KGP, compilerOptions

[boyan01]

this PR seems reverted the migrations.

I suppose an agpMajor condition for apply plugin: 'kotlin-android' is needed

[Copilot]

Pull request overview

Restores Android Kotlin compilation compatibility and prepares desktop_drop 0.8.4.

Changes:

• Applies KGP unconditionally and configures JVM 1.8.
• Bumps the package version and updates the changelog.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
packages/desktop_drop/android/build.gradle	Revises Kotlin plugin configuration.
packages/desktop_drop/pubspec.yaml	Bumps version to 0.8.4.
packages/desktop_drop/CHANGELOG.md	Documents the Android fix.

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[loucass]

@boyan01 I tried the agpMajor conditional approach first, but it fails on AGP 9 with Flutter 3.44 (which uses builtInKotlin=false). On that combination, AGP 9 does NOT provide KGP for plugin subprojects — the plugin must apply KGP itself. Skipping it causes DesktopDropPlugin class not found.

Tested here: #498 (comment)

The KGP warning is non-fatal on Flutter 3.44–3.46 (tracked at flutter/flutter#189770). When Flutter 3.47+ makes it fatal (#498 (comment)), but unconditional apply is the only approach that works on all current AGP + Flutter combinations.

Same pattern used by background_downloader: https://github.com/781flyingdutchman/background_downloader/blob/7bbf0f15330ef22427bbc019049a5ed80ae867b2/android/build.gradle#L6-L10

[loucass]

@boyan01 @ekuleshov
Update: I've now refined the approach based on your feedback. Instead of unconditional apply, I'm branching on the android.builtInKotlin Gradle property:

• builtInKotlin=false → apply KGP + kotlinOptions
• builtInKotlin=true → skip KGP + compilerOptions

This is more precise than agpMajor because it directly checks whether AGP provides Kotlin built-in, rather than guessing from the version number. It avoids the KGP warning on hosts where it's not needed.

[boyan01]

[P1] Treat a missing android.builtInKotlin property as enabled on AGP 9+

This currently maps a missing property to false, but AGP 9 and Flutter 3.47 default built-in Kotlin to enabled unless the property is explicitly set to false. With AGP 9.1 and the property omitted, this branch reaches apply plugin: kotlin-android and fails during project evaluation because AGP 9 rejects KGP while built-in Kotlin is active. I reproduced this using the checked-in Example at this PR SHA: explicit true passes, explicit false passes through the legacy path, and an absent property fails at line 26.

Please include the AGP major version in this calculation and use the same semantics as Flutter: AGP <9 is always false; AGP 9+ is true unless the property is explicitly false.

[loucass]

@boyan01
Applied. Added the agpMajor fallback so AGP 9+ defaults to builtInKotlin=true when the property is absent.

[boyan01]

Thank you for your patience in fixing this. LGTM