build: Lower JDK to 17 and minSdk to 21 (#4369)

.github/copilot-instructions.md

@@ -18,7 +18,7 @@ Meshtastic-Android is a native Android client application for the Meshtastic mes
 **ALWAYS run these commands in the exact order specified to avoid build failures:**
 
 ### Prerequisites Setup
-1. **JDK Requirement:** JDK 21 is required (will fail with other versions)
+1. **JDK Requirement:** JDK 17 is required (compatible with most developer environments)
 2. **Secrets Configuration:** Copy `secrets.defaults.properties` to `local.properties` and update:
    ```properties
    MAPS_API_KEY=your_google_maps_api_key_here
@@ -74,7 +74,7 @@ Meshtastic-Android is a native Android client application for the Meshtastic mes
 ### Environment Setup
 **Required Tools:**
 - Android SDK API 36 (compile target)
-- JDK 21 (NOT JDK 17 or 11 - build will fail)
+- JDK 17 (Preferred for consistency across project and plugins)
 - Gradle 9.0+ (downloaded automatically by wrapper)
 
 **Optional but Recommended:**
@@ -90,16 +90,17 @@ Meshtastic-Android is a native Android client application for the Meshtastic mes
 │   ├── src/androidTest/          # Instrumented tests
 │   ├── src/fdroid/              # F-Droid specific code
 │   └── src/google/              # Google Play specific code
+├── core/                         # Core library modules
 ├── network/                      # HTTP API networking library
 ├── mesh_service_example/         # AIDL service usage example
-├── buildSrc/                     # Build configuration (Configs.kt)
+├── build-logic/                  # Build configuration convention plugins
 └── config/                       # Linting and formatting configs
     ├── detekt/                   # Detekt static analysis rules
     └── spotless/                 # Code formatting configuration
 ```
 
 ### Key Configuration Files
-- `buildSrc/src/main/kotlin/Configs.kt` - Version constants and build config
+- `config.properties` - Version constants and build config
 - `app/build.gradle.kts` - Main app build configuration
 - `config/detekt/detekt.yml` - Static analysis rules
 - `config/spotless/.editorconfig` - Code formatting rules
@@ -140,7 +141,7 @@ Meshtastic-Android is a native Android client application for the Meshtastic mes
 ## Common Issues & Solutions
 
 ### Build Failures
-- **Gradle version error:** Ensure JDK 21 (NOT 17 or 11)
+- **Gradle version error:** Ensure JDK 17 (Compatible version)
 - **Missing secrets:** Copy `secrets.defaults.properties` → `local.properties`
 - **Configuration cache:** Add `--no-configuration-cache` flag if issues persist
 - **Clean state:** Always run `./gradlew clean` before debugging build issues
@@ -153,17 +154,17 @@ Meshtastic-Android is a native Android client application for the Meshtastic mes
 ### Code Style Issues
 - **Formatting:** Run `./gradlew spotlessApply` to auto-fix
 - **Detekt warnings:** Check `config/detekt/detekt.yml` for rules
-- **Localization:** Use `stringResource(R.string.key)` instead of hardcoded strings
+- **Localization:** Use `stringResource(Res.string.key)` instead of hardcoded strings
 
 ## File Organization
 
 ### Source Code Locations
-- **Main Activity:** `app/src/main/java/com/geeksville/mesh/ui/MainActivity.kt`
-- **Service Interface:** `app/src/main/aidl/com/geeksville/mesh/IMeshService.aidl`
-- **UI Screens:** `app/src/main/java/com/geeksville/mesh/ui/`
-- **Data Layer:** `app/src/main/java/com/geeksville/mesh/repository/`
-- **Database:** `app/src/main/java/com/geeksville/mesh/database/`
-- **Models:** `app/src/main/java/com/geeksville/mesh/model/`
+- **Main Activity:** `app/src/main/java/com/geeksville/mesh/MainActivity.kt`
+- **Service Interface:** `core/api/src/main/aidl/org/meshtastic/core/service/IMeshService.aidl`
+- **UI Screens:** `feature/*/src/main/kotlin/org/meshtastic/feature/*/`
+- **Data Layer:** `core/data/src/main/kotlin/org/meshtastic/core/data/`
+- **Database:** `core/database/src/main/kotlin/org/meshtastic/core/database/`
+- **Models:** `core/model/src/main/kotlin/org/meshtastic/core/model/`
 
 ### Dependencies
 - **Non-obvious deps:** Protobuf for device communication, DataDog for analytics (Google flavor)

.github/workflows/merge-queue.yml

@@ -12,8 +12,7 @@ jobs:
   lint:
     if: github.repository == 'meshtastic/Meshtastic-Android'
     uses: ./.github/workflows/reusable-lint.yml
-    secrets:
-      GRADLE_ENCRYPTION_KEY: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
+    secrets: inherit
 
   build:
     needs: lint
@@ -21,11 +20,7 @@ jobs:
     uses: ./.github/workflows/reusable-android-build.yml
     with:
       upload_artifacts: false
-    secrets:
-      GRADLE_ENCRYPTION_KEY: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
-      DATADOG_APPLICATION_ID: ${{ secrets.DATADOG_APPLICATION_ID }}
-      DATADOG_CLIENT_TOKEN: ${{ secrets.DATADOG_CLIENT_TOKEN }}
-      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+    secrets: inherit
 
   androidTest:
     needs: lint
@@ -35,9 +30,7 @@ jobs:
       api_levels: '[26, 35]' # Run on both API 26 and 35 for merge queue
       test_flavors: 'both' # Run both flavors for merge queue (comprehensive)
       upload_artifacts: false
-    secrets:
-      GRADLE_ENCRYPTION_KEY: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
-      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+    secrets: inherit
 
   check-workflow-status:
     name: Check Workflow Status  # Matches another in pull-request, and is required for merge to main.

.github/workflows/pull-request.yml

@@ -38,8 +38,7 @@ jobs:
     needs: check-changes
     if: needs.check-changes.outputs.code_changed == 'true'
     uses: ./.github/workflows/reusable-lint.yml
-    secrets:
-      GRADLE_ENCRYPTION_KEY: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
+    secrets: inherit
 
   build:
     needs: lint

.github/workflows/reusable-android-build.yml

@@ -42,10 +42,10 @@ jobs:
           fetch-depth: 0
           submodules: 'recursive'
 
-      - name: Set up JDK 21
+      - name: Set up JDK 17
         uses: actions/setup-java@v5
         with:
-          java-version: '21'
+          java-version: '17'
           distribution: 'jetbrains'
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/reusable-lint.yml

@@ -5,21 +5,25 @@ on:
     secrets:
       GRADLE_ENCRYPTION_KEY:
         required: false
+      GRADLE_CACHE_URL:
+        required: false
 
 jobs:
   lint:
     runs-on: ubuntu-latest  # Lint is fast, doesn't need large runner
     timeout-minutes: 10
+    env:
+      GRADLE_CACHE_URL: ${{ secrets.GRADLE_CACHE_URL }}
     steps:
       - name: Checkout code
         uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
-      - name: Set up JDK 21
+      - name: Set up JDK 17
         uses: actions/setup-java@v5
         with:
-          java-version: '21'
+          java-version: '17'
           distribution: 'jetbrains'
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

build-logic/convention/build.gradle.kts

@@ -25,16 +25,16 @@ plugins {
 
 group = "org.meshtastic.buildlogic"
 
-// Configure the build-logic plugins to target JDK 21
-// This matches the JDK used to build the project, and is not related to what is running on device.
+// Configure the build-logic plugins to target JDK 17
+// This improves compatibility for developers building the project or consuming its libraries.
 java {
-    sourceCompatibility = JavaVersion.VERSION_21
-    targetCompatibility = JavaVersion.VERSION_21
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
 }
 
 kotlin {
     compilerOptions {
-        jvmTarget = JvmTarget.JVM_21
+        jvmTarget = JvmTarget.JVM_17
     }
 }
 

build-logic/convention/src/main/kotlin/org/meshtastic/buildlogic/KotlinAndroid.kt

@@ -86,7 +86,9 @@ internal fun Project.configureKotlinJvm() {
  */
 private inline fun <reified T : KotlinBaseExtension> Project.configureKotlin() {
     extensions.configure<T> {
-        jvmToolchain(21)
+        // Using Java 17 for better compatibility with consumers (e.g. plugins, older environments)
+        // while still supporting modern Kotlin features.
+        jvmToolchain(17)
     }
 
     tasks.withType<KotlinCompile>().configureEach {

core/api/build.gradle.kts

@@ -35,6 +35,12 @@ afterEvaluate {
 configure<com.android.build.api.dsl.LibraryExtension> {
     namespace = "org.meshtastic.core.api"
     buildFeatures { aidl = true }
+
+    defaultConfig {
+        // Lowering minSdk to 21 for better compatibility with ATAK and other plugins
+        minSdk = 21
+    }
+
     publishing { singleVariant("googleRelease") { withSourcesJar() } }
 }
 

core/model/build.gradle.kts

@@ -42,6 +42,12 @@ configure<LibraryExtension> {
         aidl = true
     }
     namespace = "org.meshtastic.core.model"
+
+    defaultConfig {
+        // Lowering minSdk to 21 for better compatibility with ATAK and other plugins
+        minSdk = 21
+    }
+
     publishing { singleVariant("googleRelease") { withSourcesJar() } }
 }
 

core/proto/build.gradle.kts

@@ -16,22 +16,6 @@
  */
 import com.android.build.api.dsl.LibraryExtension
 
-/*
- * Copyright (c) 2025 Meshtastic LLC
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
 plugins {
     alias(libs.plugins.meshtastic.android.library)
     alias(libs.plugins.protobuf)
@@ -53,6 +37,12 @@ afterEvaluate {
 
 configure<LibraryExtension> {
     namespace = "org.meshtastic.core.proto"
+
+    defaultConfig {
+        // Lowering minSdk to 21 for better compatibility with ATAK and other plugins
+        minSdk = 21
+    }
+
     publishing { singleVariant("googleRelease") { withSourcesJar() } }
 }
 

gradle/gradle-daemon-jvm.properties

@@ -1,12 +1,2 @@
 #This file is generated by updateDaemonJvm
-toolchainUrl.FREE_BSD.AARCH64=https\://api.foojay.io/disco/v3.0/ids/ff1d4fc92bcfc9d3799beabb4e70cfa3/redirect
-toolchainUrl.FREE_BSD.X86_64=https\://api.foojay.io/disco/v3.0/ids/08ce182188ada0b93565cd9ca4a4ab32/redirect
-toolchainUrl.LINUX.AARCH64=https\://api.foojay.io/disco/v3.0/ids/c5760d82d08e6c26884debb23736ea57/redirect
-toolchainUrl.LINUX.X86_64=https\://api.foojay.io/disco/v3.0/ids/879378f84c64b2c76003b97a32968399/redirect
-toolchainUrl.MAC_OS.AARCH64=https\://api.foojay.io/disco/v3.0/ids/70ee42f1b0395356c016dbcb3e88f71d/redirect
-toolchainUrl.MAC_OS.X86_64=https\://api.foojay.io/disco/v3.0/ids/6141bf023dcc7a96c47cad75c59b054e/redirect
-toolchainUrl.UNIX.AARCH64=https\://api.foojay.io/disco/v3.0/ids/ff1d4fc92bcfc9d3799beabb4e70cfa3/redirect
-toolchainUrl.UNIX.X86_64=https\://api.foojay.io/disco/v3.0/ids/08ce182188ada0b93565cd9ca4a4ab32/redirect
-toolchainUrl.WINDOWS.AARCH64=https\://api.foojay.io/disco/v3.0/ids/3dc48436acf46a9c2958682158988183/redirect
-toolchainUrl.WINDOWS.X86_64=https\://api.foojay.io/disco/v3.0/ids/d935bdb25150f4573137eb8176e8b4ec/redirect
-toolchainVersion=21
+toolchainVersion=17

jitpack.yml

@@ -1,5 +1,5 @@
 jdk:
-  - openjdk21
+  - openjdk17
 before_install:
   - ./gradlew :core:proto:generateGoogleReleaseProto
 install: