Inform Gradle where to locate pre-installed JDKs

.github/workflows/integ-test-detect-java-toolchains.yml

@@ -80,3 +80,27 @@ jobs:
       run: | 
         grep -q 'Eclipse Temurin JDK 16' output.txt || (echo "::error::Did not detect setup-java installed JDK 16" && exit 1)
         grep -q 'Eclipse Temurin JDK 20' output.txt || (echo "::error::Did not detect setup-java installed JDK 20" && exit 1)
+
+  # Test that predefined JDK detection property is not overwritten by action
+  check-no-overwrite:
+    strategy:
+      matrix:
+        os: ${{fromJSON(inputs.runner-os)}}
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Checkout sources
+      uses: actions/checkout@v3
+    - name: Download distribution if required
+      uses: ./.github/actions/download-dist
+    - name: Configure java installations env var in Gradle User Home
+      shell: bash
+      run: | 
+        mkdir -p ~/.gradle
+        echo "org.gradle.java.installations.fromEnv=XXXXX" > ~/.gradle/gradle.properties
+    - name: Setup Gradle
+      uses: ./
+    - name: Check gradle.properties
+      shell: bash
+      run: |
+        cat ~/.gradle/gradle.properties
+        grep -q 'org.gradle.java.installations.fromEnv=JAVA_HOME' && exit 1

src/cache-base.ts

@@ -172,6 +172,22 @@ export class GradleStateCache {
     }
 
     private initializeGradleUserHome(gradleUserHome: string, initScriptsDir: string): void {
+        // Ensure that pre-installed java versions are detected. Only add property if it isn't already defined.
+        const gradleProperties = path.resolve(gradleUserHome, 'gradle.properties')
+        const existingGradleProperties = fs.existsSync(gradleProperties)
+            ? fs.readFileSync(gradleProperties, 'utf8')
+            : ''
+        if (!existingGradleProperties.includes('org.gradle.java.installations.fromEnv=')) {
+            fs.appendFileSync(
+                gradleProperties,
+                `
+# Auto-detect pre-installed JDKs
+org.gradle.java.installations.fromEnv=JAVA_HOME_8_X64,JAVA_HOME_11_X64,JAVA_HOME_17_X64
+`
+            )
+        }
+
+        // Copy init scripts from src/resources
         const initScriptFilenames = [
             'build-result-capture.init.gradle',
             'build-result-capture-service.plugin.groovy',