Improve error messages when using outdated Java or Gradle.

.github/workflows/test-push.yml

@@ -90,3 +90,53 @@ jobs:
         with:
           name: Reproducible Build ${{ matrix.os }} (${{ matrix.java }}) Results
           path: build/reports/
+
+  bootstrap_tests:
+    needs: build
+
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [ 8, 11, 15, 16 ]
+        gradle: [ 4.9, 5.2, 6.0.1, 6.9, 7.0.2 ]
+        exclude:
+          - java: 16
+            gradle: 6.9
+          - java: 16
+            gradle: 6.0.1
+          - java: 16
+            gradle: 5.2
+          - java: 16
+            gradle: 4.9
+          - java: 15
+            gradle: 6.0.1
+          - java: 15
+            gradle: 5.2
+          - java: 15
+            gradle: 4.9
+    runs-on: ubuntu-20.04
+    container:
+      image: gradle:7.0.2-jdk16
+      options: --user root
+
+    steps:
+      # Build loom and publish to maven local
+      - uses: actions/checkout@v2
+      - run: gradle build publishToMavenLocal -x test -x check
+
+      - run: gradle wrapper --gradle-version=${{ matrix.gradle }}
+        working-directory: bootstrap/test-project
+      - run: gradle --stop
+
+      - uses: actions/setup-java@v2
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: 'adopt'
+
+      - run: ./gradlew --version
+        working-directory: bootstrap/test-project
+      - run: ./gradlew build
+        working-directory: bootstrap/test-project
+        continue-on-error: true
+
+      # TODO check the output of the previous step here

.gitignore

@@ -21,3 +21,4 @@
 !/Jenkinsfile
 !/checkstyle.xml
 !/codenarc.groovy
+!/bootstrap

bootstrap/.gitignore

@@ -0,0 +1,7 @@
+# Ignore everything
+/*
+
+!/src
+!/build.gradle
+!/.gitignore
+!/test-project

bootstrap/build.gradle

@@ -0,0 +1,30 @@
+plugins {
+	id 'java'
+	id 'groovy'
+}
+
+sourceCompatibility = 8
+targetCompatibility = 8
+
+tasks.withType(JavaCompile).configureEach {
+	it.options.encoding = "UTF-8"
+	it.options.release = 8
+}
+
+repositories {
+	mavenCentral()
+}
+
+dependencies {
+	implementation gradleApi()
+
+	testImplementation(gradleTestKit())
+	testImplementation('org.spockframework:spock-core:2.0-M5-groovy-3.0') {
+		exclude module: 'groovy-all'
+	}
+}
+
+test {
+	maxHeapSize = "4096m"
+	useJUnitPlatform()
+}

bootstrap/src/main/java/net/fabricmc/loom/bootstrap/BootstrappedPlugin.java

@@ -0,0 +1,7 @@
+package net.fabricmc.loom.bootstrap;
+
+import org.gradle.api.plugins.PluginAware;
+
+public interface BootstrappedPlugin {
+	void apply(PluginAware project);
+}

bootstrap/src/main/java/net/fabricmc/loom/bootstrap/LoomGradlePluginBootstrap.java

@@ -0,0 +1,67 @@
+package net.fabricmc.loom.bootstrap;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.gradle.api.JavaVersion;
+import org.gradle.api.Plugin;
+import org.gradle.api.plugins.PluginAware;
+import org.gradle.util.GradleVersion;
+
+/**
+ * This bootstrap is compiled against a minimal gradle API and java 8, this allows us to show a nice error to users who run on unsupported configurations.
+ */
+@SuppressWarnings("unused")
+public class LoomGradlePluginBootstrap implements Plugin<PluginAware> {
+	private static final int MIN_SUPPORTED_MAJOR_GRADLE_VERSION = 7;
+	private static final int MIN_SUPPORTED_MAJOR_JAVA_VERSION = 16;
+
+	private static final String PLUGIN_CLASS_NAME = "net.fabricmc.loom.LoomGradlePlugin";
+
+	@Override
+	public void apply(PluginAware project) {
+		List<String> errors = new ArrayList<>();
+
+		if (!isValidGradleRuntime()) {
+			errors.add(String.format("You are using an outdated version of Gradle (%s). Gradle %d or higher is required.", GradleVersion.current().getVersion(), MIN_SUPPORTED_MAJOR_GRADLE_VERSION));
+		}
+
+		if (!isValidJavaRuntime()) {
+			errors.add(String.format("You are using an outdated version of Java (%s). Java %d or higher is required.", JavaVersion.current().getMajorVersion(), MIN_SUPPORTED_MAJOR_JAVA_VERSION));
+
+			String javaHome = System.getenv("JAVA_HOME");
+
+			if (javaHome != null) {
+				errors.add(String.format("The JAVA_HOME environment variable is currently set to (%s).", javaHome));
+			}
+		}
+
+		if (!errors.isEmpty()) {
+			throw new UnsupportedOperationException(String.join("\n", errors));
+		}
+
+		getActivePlugin().apply(project);
+	}
+
+	private static boolean isValidJavaRuntime() {
+		// Note use compareTo to ensure compatibility with gradle < 6.0
+		return JavaVersion.current().compareTo(JavaVersion.toVersion(MIN_SUPPORTED_MAJOR_JAVA_VERSION)) >= 0;
+	}
+
+	private static boolean isValidGradleRuntime() {
+		return getMajorGradleVersion() >= MIN_SUPPORTED_MAJOR_GRADLE_VERSION;
+	}
+
+	private static int getMajorGradleVersion() {
+		String version = GradleVersion.current().getVersion();
+		return Integer.parseInt(version.substring(0, version.indexOf(".")));
+	}
+
+	BootstrappedPlugin getActivePlugin() {
+		try {
+			return (BootstrappedPlugin) Class.forName(PLUGIN_CLASS_NAME).getConstructor().newInstance();
+		} catch (Exception e) {
+			throw new RuntimeException("Failed to bootstrap loom", e);
+		}
+	}
+}

bootstrap/src/main/resources/META-INF/trick-gradle-into-thinking-loom-is-signed.SF

@@ -0,0 +1,4 @@
+Trick gradle into thinking that loom is signed to skip over transforming all classes in the jar.
+This is required to get the bootstrap to well bootstrap on older gradle versions that dont support java 16.
+
+See https://github.com/gradle/gradle/blob/master/subprojects/core/src/main/java/org/gradle/internal/classpath/InstrumentingClasspathFileTransformer.java#L129

bootstrap/test-project/build.gradle

@@ -0,0 +1,8 @@
+plugins {
+	id 'fabric-loom' version '0.8.local'
+}
+
+dependencies {
+	minecraft "com.mojang:minecraft:1.16.5"
+	mappings loom.officialMojangMappings()
+}

bootstrap/test-project/settings.gradle

@@ -0,0 +1,10 @@
+pluginManagement {
+    repositories {
+        maven {
+            name = 'Fabric'
+            url = 'https://maven.fabricmc.net/'
+        }
+        gradlePluginPortal()
+		mavenLocal()
+    }
+}

build.gradle

@@ -39,9 +39,19 @@ repositories {
 	mavenCentral()
 }
 
+configurations {
+	bootstrap {
+		transitive false
+	}
+	compileClasspath.extendsFrom bootstrap
+	runtimeClasspath.extendsFrom bootstrap
+}
+
 dependencies {
 	implementation gradleApi()
 
+	bootstrap project(":bootstrap")
+
 	// libraries
 	implementation ('commons-io:commons-io:2.8.0')
 	implementation ('org.zeroturnaround:zt-zip:1.14')
@@ -71,7 +81,7 @@ dependencies {
 	implementation ('org.cadixdev:lorenz-io-proguard:0.5.6')
 
 	// decompilers
-	implementation ('net.fabricmc:fabric-fernflower:1.4.0')
+	implementation ('net.fabricmc:fabric-fernflower:1.4.1')
 	implementation ('org.benf:cfr:0.151')
 
 	// source code remapping
@@ -94,6 +104,8 @@ jar {
 	manifest {
 		attributes 'Implementation-Version': project.version
 	}
+
+	from configurations.bootstrap.collect { it.isDirectory() ? it : zipTree(it) }
 }
 
 task sourcesJar(type: Jar, dependsOn: classes) {
@@ -128,7 +140,7 @@ gradlePlugin {
 	plugins {
 		fabricLoom {
 			id = 'fabric-loom'
-			implementationClass = 'net.fabricmc.loom.LoomGradlePlugin'
+			implementationClass = 'net.fabricmc.loom.bootstrap.LoomGradlePluginBootstrap'
 		}
 	}
 }
@@ -215,6 +227,21 @@ publishing {
 	}
 }
 
+// Need to tweak this file to pretend we are compatible with j8 so the bootstrap will run.
+tasks.withType(GenerateModuleMetadata) {
+	doLast {
+		def file = outputFile.get().asFile
+
+		def metadata = new groovy.json.JsonSlurper().parseText(file.text)
+
+		metadata.variants.each {
+			it.attributes["org.gradle.jvm.version"] = 8
+		}
+
+		file.text = groovy.json.JsonOutput.toJson(metadata)
+	}
+}
+
 // A task to output a json file with a list of all the test to run
 task writeActionsTestMatrix() {
 	doLast {

settings.gradle

@@ -1,2 +1,3 @@
 rootProject.name = name
 
+include "bootstrap"

src/main/java/net/fabricmc/loom/LoomGradlePlugin.java

@@ -29,10 +29,10 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.common.collect.ImmutableMap;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
-import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.plugins.PluginAware;
 
+import net.fabricmc.loom.bootstrap.BootstrappedPlugin;
 import net.fabricmc.loom.configuration.CompileConfiguration;
 import net.fabricmc.loom.configuration.FabricApiExtension;
 import net.fabricmc.loom.configuration.MavenPublication;
@@ -41,7 +41,7 @@ import net.fabricmc.loom.configuration.providers.mappings.MappingsCache;
 import net.fabricmc.loom.decompilers.DecompilerConfiguration;
 import net.fabricmc.loom.task.LoomTasks;
 
-public class LoomGradlePlugin implements Plugin<PluginAware> {
+public class LoomGradlePlugin implements BootstrappedPlugin {
 	public static boolean refreshDeps;
 	public static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
 	public static final ObjectMapper OBJECT_MAPPER = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);