[DON-2469] chore: update Gradle to 9.1 and address warnings in build … (#2559)

* [DON-2469] chore: update Gradle to 9.1 and address warnings in build scripts

Co-authored-by: Claude <noreply@anthropic.com>

* feat: add Backpack Android plugins for application, library, and publishing

Co-authored-by: Claude <noreply@anthropic.com>

* update kotlin version

Co-authored-by: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: lokmane.krizou@skyscanner.net <lokmane.krizou@skyscanner.net>

Author: 3 people

build-logic/conventions/build.gradle.kts

@@ -18,6 +18,8 @@
 
 plugins {
     `kotlin-dsl`
+    `java-gradle-plugin`
+    alias(libs.plugins.kotlin.jvm)
 }
 
 dependencies {
@@ -29,3 +31,28 @@ java {
     sourceCompatibility = JavaVersion.VERSION_17
     targetCompatibility = JavaVersion.VERSION_17
 }
+
+kotlin {
+    jvmToolchain(17)
+}
+
+gradlePlugin {
+    plugins {
+        register("backpackAndroidLibrary") {
+            id = "backpack.android-library"
+            implementationClass = "net.skyscanner.backpack.conventions.BackpackAndroidLibraryPlugin"
+        }
+        register("backpackAndroidApp") {
+            id = "backpack.android-app"
+            implementationClass = "net.skyscanner.backpack.conventions.BackpackAndroidAppPlugin"
+        }
+        register("backpackKotlinLibrary") {
+            id = "backpack.kotlin-library"
+            implementationClass = "net.skyscanner.backpack.conventions.BackpackKotlinLibraryPlugin"
+        }
+        register("backpackPublishing") {
+            id = "backpack.publishing"
+            implementationClass = "net.skyscanner.backpack.conventions.BackpackPublishingPlugin"
+        }
+    }
+}

build-logic/conventions/src/main/kotlin/backpack.android-app.gradle.kts

@@ -0,0 +1,85 @@
+/**
+ * Backpack for Android - Skyscanner's Design System
+ *
+ * Copyright 2018 - 2026 Skyscanner Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.skyscanner.backpack.conventions
+
+import SdkVersions
+import com.android.build.gradle.internal.dsl.BaseAppModuleExtension
+import org.gradle.api.JavaVersion
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.configure
+import org.gradle.kotlin.dsl.withType
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
+class BackpackAndroidAppPlugin : Plugin<Project> {
+    override fun apply(target: Project) {
+        with(target) {
+            plugins.apply("com.android.application")
+            plugins.apply("org.jetbrains.kotlin.android")
+
+            extensions.configure<BaseAppModuleExtension> {
+                compileSdk = SdkVersions.COMPILE_SDK
+
+                defaultConfig {
+                    minSdk = SdkVersions.MIN_SDK
+                    testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+                }
+
+                compileOptions {
+                    sourceCompatibility = JavaVersion.VERSION_17
+                    targetCompatibility = JavaVersion.VERSION_17
+                }
+
+                testOptions {
+                    animationsDisabled = true
+                    unitTests {
+                        isIncludeAndroidResources = true
+                    }
+                }
+
+                buildFeatures {
+                    compose = true
+                }
+
+                packaging {
+                    resources.excludes.add("**/attach_hotspot_windows.dll")
+                    resources.excludes.add("META-INF/licenses/**")
+                    resources.excludes.add("META-INF/AL2.0")
+                    resources.excludes.add("META-INF/LGPL2.1")
+                }
+            }
+
+            extensions.configure<KotlinAndroidProjectExtension> {
+                jvmToolchain(17)
+            }
+
+            tasks.withType<KotlinCompile>().configureEach {
+                compilerOptions {
+                    jvmTarget.set(JvmTarget.JVM_17)
+                    freeCompilerArgs.addAll(
+                        "-opt-in=kotlin.RequiresOptIn",
+                        "-opt-in=net.skyscanner.backpack.util.InternalBackpackApi",
+                    )
+                }
+            }
+        }
+    }
+}