Support Java Agents published by the platform

src/main/java/net/neoforged/moddevgradle/internal/ModDevRunWorkflow.java

@@ -27,6 +27,7 @@
 import org.gradle.api.attributes.Usage;
 import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.file.Directory;
+import org.gradle.api.file.FileCollection;
 import org.gradle.api.file.RegularFile;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.JavaPluginExtension;
@@ -61,6 +62,7 @@ public class ModDevRunWorkflow {
     private final ModuleDependency gameLibrariesDependency;
     private final Configuration additionalClasspath;
     private final Configuration userDevConfigOnly;
+    private final Configuration javaAgent;
 
     /**
      * @param gameLibrariesDependency A module dependency that represents the library dependencies of the game.
@@ -74,6 +76,7 @@ private ModDevRunWorkflow(Project project,
             @Nullable ModuleDependency modulePathDependency,
             @Nullable ModuleDependency runTypesConfigDependency,
             @Nullable ModuleDependency testFixturesDependency,
+            @Nullable ModuleDependency javaAgentDependency,
             ModuleDependency gameLibrariesDependency,
             DomainObjectCollection<RunModel> runs,
             VersionCapabilitiesInternal versionCapabilities) {
@@ -97,6 +100,16 @@ private ModDevRunWorkflow(Project project,
             }
         });
 
+        javaAgent = configurations.create("neoForgeJavaAgent", spec -> {
+            spec.setDescription("Any jar in this configuration will be added as a javagent to the Minecraft and JUnit command lines in this project.");
+            spec.setCanBeResolved(true);
+            spec.setCanBeConsumed(false);
+            spec.setTransitive(false); // Java agents can't load transitive dependencies
+            if (javaAgentDependency != null) {
+                spec.getDependencies().add(javaAgentDependency);
+            }
+        });
+
         additionalClasspath = configurations.create("additionalRuntimeClasspath", spec -> {
             spec.setDescription("Contains dependencies of every run, that should not be considered boot classpath modules.");
             spec.setCanBeResolved(true);
@@ -149,6 +162,7 @@ public static ModDevRunWorkflow create(Project project,
                 dependencies.modulePathDependency(),
                 dependencies.runTypesConfigDependency(),
                 dependencies.testFixturesDependency(),
+                dependencies.javaAgentDependency(),
                 dependencies.gameLibrariesDependency(),
                 runs,
                 versionCapabilites);
@@ -198,7 +212,8 @@ public void configureTesting(Provider<ModModel> testedMod, Provider<Set<ModModel
                         legacyClassPath.getDependencies().add(gameLibrariesDependency);
                         addClientResources(project, legacyClassPath, artifactsWorkflow.createArtifacts());
                     },
-                    artifactsWorkflow.downloadAssets().flatMap(DownloadAssets::getAssetPropertiesFile));
+                    artifactsWorkflow.downloadAssets().flatMap(DownloadAssets::getAssetPropertiesFile),
+                    javaAgent);
         }
     }
 
@@ -404,7 +419,8 @@ static void setupTestTask(Project project,
             Provider<Directory> argFileDir,
             Consumer<Configuration> configureModulePath,
             Consumer<Configuration> configureLegacyClasspath,
-            Provider<RegularFile> assetPropertiesFile) {
+            Provider<RegularFile> assetPropertiesFile,
+            FileCollection javaAgent) {
         var gameDirectory = new File(project.getProjectDir(), JUNIT_GAME_DIR);
 
         var ideIntegration = IdeIntegration.of(project, branding);
@@ -455,6 +471,7 @@ static void setupTestTask(Project project,
             task.getProgramArgsFile().set(programArgsFile);
             task.getLog4jConfigFile().set(log4j2ConfigFile);
             task.getRunTypeTemplatesSource().from(runTemplatesSourceFile);
+            task.getJavaAgent().from(javaAgent);
             task.getModules().from(neoForgeModDevModules);
             task.getLegacyClasspathFile().set(writeLcpTask.get().getLegacyClasspathFile());
             task.getAssetProperties().set(assetPropertiesFile);

src/main/java/net/neoforged/moddevgradle/internal/ModdingDependencies.java

@@ -11,6 +11,7 @@ public record ModdingDependencies(
         @Nullable ModuleDependency neoFormDependency,
         @Nullable String neoFormDependencyNotation,
         ModuleDependency gameLibrariesDependency,
+        @Nullable ModuleDependency javaAgentDependency,
         @Nullable ModuleDependency modulePathDependency,
         @Nullable ModuleDependency runTypesConfigDependency,
         @Nullable ModuleDependency testFixturesDependency) {
@@ -34,12 +35,19 @@ public static ModdingDependencies create(ModuleDependency neoForge,
                     .capabilities(caps -> caps.requireCapability("net.neoforged:neoforge-moddev-test-fixtures"));
         }
 
+        ModuleDependency javaAgentDependency = null;
+        if (versionCapabilities.javaAgent()) {
+            javaAgentDependency = neoForge.copy()
+                    .capabilities(caps -> caps.requireCapability("net.neoforged:neoforge-javaagent"));
+        }
+
         return new ModdingDependencies(
                 neoForge,
                 neoForgeNotation,
                 neoForm,
                 neoFormNotation,
                 librariesDependency,
+                javaAgentDependency,
                 modulePathDependency,
                 runTypesDataDependency,
                 testFixturesDependency);
@@ -57,6 +65,7 @@ public static ModdingDependencies createVanillaOnly(ModuleDependency neoForm, St
                 librariesDependency,
                 null,
                 null,
+                null,
                 null);
     }
 }

src/main/java/net/neoforged/moddevgradle/internal/NeoDevFacade.java

@@ -83,7 +83,8 @@ public static void setupTestTask(Project project,
                 argFileDir,
                 configureModulePath,
                 configureAdditionalClasspath,
-                assetPropertiesFile);
+                assetPropertiesFile,
+                project.files());
     }
 
     public static void runTaskOnProjectSync(Project project, Object task) {

src/main/java/net/neoforged/moddevgradle/internal/PrepareRunOrTest.java

@@ -82,6 +82,10 @@ abstract class PrepareRunOrTest extends DefaultTask {
     @InputFiles
     abstract ConfigurableFileCollection getModules();
 
+    @Classpath
+    @InputFiles
+    abstract ConfigurableFileCollection getJavaAgent();
+
     @Input
     public abstract MapProperty<String, String> getSystemProperties();
 
@@ -224,6 +228,10 @@ private UserDevConfig getSimulatedUserDevConfigForVanilla() {
     private void writeJvmArguments(UserDevRunType runConfig, Map<String, String> additionalProperties) throws IOException {
         var lines = new ArrayList<String>();
 
+        for (var file : getJavaAgent()) {
+            lines.add("-javaagent:" + file.getAbsolutePath());
+        }
+
         lines.addAll(getInterpolatedJvmArgs(runConfig));
 
         var userJvmArgs = getJvmArguments().get();

src/main/java/net/neoforged/moddevgradle/internal/utils/VersionCapabilitiesInternal.java

@@ -14,9 +14,12 @@
  * @param javaVersion      Which Java version Vanilla uses to compile and run.
  * @param splitDataRuns    Whether Vanilla has separate main classes for generating client and server data.
  * @param testFixtures     If the NeoForge version for this Minecraft version supports test fixtures.
+ * @param modLocatorRework Has the rework of FML mod locators that allow the client resources to use any jar filename. If false, the client resource jar must be called "client-extra".
+ * @param javaAgent        If true, the NeoForge dependency supplies a java agent capability.
  */
 public record VersionCapabilitiesInternal(String minecraftVersion, int javaVersion, boolean splitDataRuns,
-        boolean testFixtures, boolean modLocatorRework) implements VersionCapabilities, Serializable {
+        boolean testFixtures, boolean modLocatorRework,
+        boolean javaAgent) implements VersionCapabilities, Serializable {
 
     private static final Logger LOG = LoggerFactory.getLogger(VersionCapabilitiesInternal.class);
 
@@ -26,6 +29,8 @@ public record VersionCapabilitiesInternal(String minecraftVersion, int javaVersi
     // Strips NeoForm timestamp suffixes OR dynamic version markers
     private static final Pattern NEOFORM_PATTERN = Pattern.compile("^(.*)-(?:\\+|\\d{8}\\.\\d{6})$");
 
+    // TODO: Wrong but for testing it's 1.20.1 for now
+    private static final int MC_1_21_4_INDEX = getReferenceVersionIndex("1.21.1");
     private static final int MC_24W45A_INDEX = getReferenceVersionIndex("24w45a");
     private static final int MC_1_20_5_INDEX = getReferenceVersionIndex("1.20.5");
     private static final int MC_24W14A_INDEX = getReferenceVersionIndex("24w14a");
@@ -56,8 +61,9 @@ public static VersionCapabilitiesInternal ofVersionIndex(int versionIndex, Strin
         var splitData = hasSplitDataEntrypoints(versionIndex);
         var testFixtures = hasTestFixtures(versionIndex);
         var modLocatorRework = hasModLocatorRework(versionIndex);
+        var javaAgent = hasJavaAgent(versionIndex);
 
-        return new VersionCapabilitiesInternal(minecraftVersion, javaVersion, splitData, testFixtures, modLocatorRework);
+        return new VersionCapabilitiesInternal(minecraftVersion, javaVersion, splitData, testFixtures, modLocatorRework, javaAgent);
     }
 
     static int getJavaVersion(int versionIndex) {
@@ -84,6 +90,10 @@ static boolean hasModLocatorRework(int versionIndex) {
         return versionIndex <= MC_1_20_5_INDEX;
     }
 
+    static boolean hasJavaAgent(int versionIndex) {
+        return versionIndex <= MC_1_21_4_INDEX;
+    }
+
     static int indexOfNeoForgeVersion(String version) {
         // NeoForge omits the "1." at the start of the Minecraft version and just adds an incrementing last digit
         var matcher = NEOFORGE_PATTERN.matcher(version);
@@ -168,6 +178,7 @@ public VersionCapabilitiesInternal withMinecraftVersion(String minecraftVersion)
                 javaVersion,
                 splitDataRuns,
                 testFixtures,
-                modLocatorRework);
+                modLocatorRework,
+                javaAgent);
     }
 }