Allow foreign programs to discover and resolve mods without launching the game

src/main/java/net/fabricmc/loader/impl/FabricLoaderImpl.java

@@ -51,6 +51,7 @@
 import net.fabricmc.loader.impl.discovery.DirectoryModCandidateFinder;
 import net.fabricmc.loader.impl.discovery.ModCandidateImpl;
 import net.fabricmc.loader.impl.discovery.ModDiscoverer;
+import net.fabricmc.loader.impl.discovery.ModDiscoveryInfo;
 import net.fabricmc.loader.impl.discovery.ModResolutionException;
 import net.fabricmc.loader.impl.discovery.ModResolver;
 import net.fabricmc.loader.impl.discovery.RuntimeModRemapper;
@@ -207,13 +208,19 @@ private void setup() throws ModResolutionException {
 
 		// discover mods
 
-		ModDiscoverer discoverer = new ModDiscoverer(versionOverrides, depOverrides);
+		ModDiscoverer discoverer = new ModDiscoverer(this.provider, this.isDevelopmentEnvironment(), this.getEnvironmentType(), versionOverrides, depOverrides);
 		discoverer.addCandidateFinder(new ClasspathModCandidateFinder());
 		discoverer.addCandidateFinder(new DirectoryModCandidateFinder(getModsDirectory0(), remapRegularMods));
 		discoverer.addCandidateFinder(new ArgumentModCandidateFinder(remapRegularMods));
 
 		Map<String, Set<ModCandidateImpl>> envDisabledMods = new HashMap<>();
-		modCandidates = discoverer.discoverMods(this, envDisabledMods);
+		final ModDiscoveryInfo discoveryInfo = discoverer.discoverMods(envDisabledMods);
+
+		if (!discoveryInfo.launchable()) {
+			throw discoveryInfo.getException();
+		}
+
+		modCandidates = discoveryInfo.getFoundMods();
 
 		// dump version and dependency overrides info
 

src/main/java/net/fabricmc/loader/impl/discovery/ModDiscoverer.java

@@ -49,9 +49,9 @@
 import net.fabricmc.api.EnvType;
 import net.fabricmc.loader.api.SemanticVersion;
 import net.fabricmc.loader.api.metadata.ModMetadata;
-import net.fabricmc.loader.impl.FabricLoaderImpl;
 import net.fabricmc.loader.impl.FormattedException;
 import net.fabricmc.loader.impl.discovery.ModCandidateFinder.ModCandidateConsumer;
+import net.fabricmc.loader.impl.game.GameDefinition;
 import net.fabricmc.loader.impl.game.GameProvider.BuiltinMod;
 import net.fabricmc.loader.impl.metadata.BuiltinModMetadata;
 import net.fabricmc.loader.impl.metadata.DependencyOverrides;
@@ -71,25 +71,31 @@ public final class ModDiscoverer {
 	private final VersionOverrides versionOverrides;
 	private final DependencyOverrides depOverrides;
 	private final List<ModCandidateFinder> candidateFinders = new ArrayList<>();
-	private final EnvType envType = FabricLoaderImpl.INSTANCE.getEnvironmentType();
+	private final EnvType envType;
 	private final Map<Long, ModScanTask> jijDedupMap = new ConcurrentHashMap<>(); // avoids reading the same jar twice
 	private final List<NestedModInitData> nestedModInitDatas = Collections.synchronizedList(new ArrayList<>()); // breaks potential cycles from deduplication
 	private final List<Path> nonFabricMods = Collections.synchronizedList(new ArrayList<>());
+	private final GameDefinition gameDefinition;
+	private final boolean isDevelopment;
 
-	public ModDiscoverer(VersionOverrides versionOverrides, DependencyOverrides depOverrides) {
+	public ModDiscoverer(GameDefinition gameDefinition, boolean isDevelopment, EnvType environment, VersionOverrides versionOverrides, DependencyOverrides depOverrides) {
 		this.versionOverrides = versionOverrides;
 		this.depOverrides = depOverrides;
+		this.envType = environment;
+		this.gameDefinition = gameDefinition;
+		this.isDevelopment = isDevelopment;
 	}
 
 	public void addCandidateFinder(ModCandidateFinder f) {
 		candidateFinders.add(f);
 	}
 
-	public List<ModCandidateImpl> discoverMods(FabricLoaderImpl loader, Map<String, Set<ModCandidateImpl>> envDisabledModsOut) throws ModResolutionException {
+	public ModDiscoveryInfo discoverMods(Map<String, Set<ModCandidateImpl>> envDisabledModsOut) throws ModResolutionException {
 		long startTime = System.nanoTime();
 		ForkJoinPool pool = new ForkJoinPool();
 		Set<Path> processedPaths = new HashSet<>(); // suppresses duplicate paths
 		List<Future<ModCandidateImpl>> futures = new ArrayList<>();
+		List<Exception> exceptions = new ArrayList<>();
 
 		ModCandidateConsumer taskSubmitter = (paths, requiresRemap) -> {
 			List<Path> pendingPaths = new ArrayList<>(paths.size());
@@ -114,24 +120,24 @@ public List<ModCandidateImpl> discoverMods(FabricLoaderImpl loader, Map<String,
 		List<ModCandidateImpl> candidates = new ArrayList<>();
 
 		// add builtin mods
-		for (BuiltinMod mod : loader.getGameProvider().getBuiltinMods()) {
+		for (BuiltinMod mod : gameDefinition.getBuiltinMods()) {
 			if (!(mod.metadata.getVersion() instanceof SemanticVersion)) {
 				String error = String.format("%s uses the non-semantic version %s, which doesn't support range comparisons and may cause mod dependencies against it to fail unexpectedly. Consider updating Fabric Loader or explicitly specifying the game version with the fabric.gameVersion system property.",
 						mod.metadata.getId(), mod.metadata.getVersion());
 
-				if (loader.isDevelopmentEnvironment()) { // fail hard in-dev
+				if (isDevelopment) { // fail hard in-dev
 					throw new FormattedException("Invalid game version", error);
 				} else {
 					Log.warn(LogCategory.GENERAL, error);
 				}
 			}
 
 			ModCandidateImpl candidate = ModCandidateImpl.createBuiltin(mod, versionOverrides, depOverrides);
-			candidates.add(MetadataVerifier.verifyIndev(candidate, loader.isDevelopmentEnvironment()));
+			candidates.add(MetadataVerifier.verifyIndev(candidate, isDevelopment));
 		}
 
 		// Add the current Java version
-		candidates.add(MetadataVerifier.verifyIndev(createJavaMod(), loader.isDevelopmentEnvironment()));
+		candidates.add(MetadataVerifier.verifyIndev(createJavaMod(), isDevelopment));
 
 		ModResolutionException exception = null;
 
@@ -178,10 +184,6 @@ public List<ModCandidateImpl> discoverMods(FabricLoaderImpl loader, Map<String,
 			throw new FormattedException("Mod discovery interrupted!", e);
 		}
 
-		if (exception != null) {
-			throw exception;
-		}
-
 		// get optional set of disabled mod ids
 		Set<String> disabledModIds = findDisabledModIds();
 
@@ -214,7 +216,7 @@ public List<ModCandidateImpl> discoverMods(FabricLoaderImpl loader, Map<String,
 
 		Log.debug(LogCategory.DISCOVERY, "Mod discovery time: %.1f ms", (endTime - startTime) * 1e-6);
 
-		return new ArrayList<>(ret);
+		return new ModDiscoveryInfo(new ArrayList<>(ret), exception);
 	}
 
 	public List<Path> getNonFabricMods() {
@@ -372,7 +374,7 @@ public RewindableInputStream getInputStream() throws IOException {
 						private ZipEntry currentEntry;
 					});
 
-					if (!nestedJarPaths.isEmpty() && FabricLoaderImpl.INSTANCE.isDevelopmentEnvironment()) {
+					if (!nestedJarPaths.isEmpty() && isDevelopment) {
 						Log.warn(LogCategory.METADATA, "Mod %s %s references missing nested jars: %s", metadata.getId(), metadata.getVersion(), nestedJarPaths);
 					}
 				}
@@ -450,7 +452,7 @@ public RewindableInputStream getInputStream() throws IOException {
 					});
 				}
 
-				if (!nestedJarPaths.isEmpty() && FabricLoaderImpl.INSTANCE.isDevelopmentEnvironment()) {
+				if (!nestedJarPaths.isEmpty() && isDevelopment) {
 					Log.warn(LogCategory.METADATA, "Mod %s %s references missing nested jars: %s", metadata.getId(), metadata.getVersion(), nestedJarPaths);
 				}
 			}
@@ -507,7 +509,7 @@ private List<ModScanTask> computeNestedMods(ZipEntrySource entrySource) throws I
 		}
 
 		private LoaderModMetadata parseMetadata(InputStream is, String localPath) throws ParseMetadataException {
-			return ModMetadataParser.parseMetadata(is, localPath, parentPaths, versionOverrides, depOverrides, FabricLoaderImpl.INSTANCE.isDevelopmentEnvironment());
+			return ModMetadataParser.parseMetadata(is, localPath, parentPaths, versionOverrides, depOverrides, isDevelopment);
 		}
 	}
 

src/main/java/net/fabricmc/loader/impl/discovery/ModDiscoveryInfo.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2016 FabricMC
+ *
+ * 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.fabricmc.loader.impl.discovery;
+
+import java.util.List;
+
+public class ModDiscoveryInfo {
+	private final List<ModCandidateImpl> modsFound;
+	private final ModResolutionException exception;
+
+	public ModDiscoveryInfo(List<ModCandidateImpl> discoveredMods, ModResolutionException exception) {
+		this.modsFound = discoveredMods;
+		this.exception = exception;
+	}
+
+	public List<ModCandidateImpl> getFoundMods() {
+		return modsFound;
+	}
+
+	public ModResolutionException getException() {
+		return exception;
+	}
+
+	public boolean launchable() {
+		return exception == null;
+	}
+}

src/main/java/net/fabricmc/loader/impl/game/GameDefinition.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2016 FabricMC
+ *
+ * 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.fabricmc.loader.impl.game;
+
+import java.nio.file.Path;
+import java.util.Collection;
+
+import net.fabricmc.loader.impl.game.GameProvider.BuiltinMod;
+
+public interface GameDefinition {
+	String getGameId();
+	String getGameName();
+	String getRawGameVersion();
+	String getNormalizedGameVersion();
+	Collection<BuiltinMod> getBuiltinMods();
+	Path getLaunchDirectory();
+}
+

src/main/java/net/fabricmc/loader/impl/game/GameProvider.java

@@ -17,7 +17,6 @@
 package net.fabricmc.loader.impl.game;
 
 import java.nio.file.Path;
-import java.util.Collection;
 import java.util.List;
 import java.util.Objects;
 
@@ -27,15 +26,9 @@
 import net.fabricmc.loader.impl.util.Arguments;
 import net.fabricmc.loader.impl.util.LoaderUtil;
 
-public interface GameProvider { // name directly referenced in net.fabricmc.loader.impl.launch.knot.Knot.findEmbedddedGameProvider() and service loader records
-	String getGameId();
-	String getGameName();
-	String getRawGameVersion();
-	String getNormalizedGameVersion();
-	Collection<BuiltinMod> getBuiltinMods();
+public interface GameProvider extends GameDefinition { // name directly referenced in net.fabricmc.loader.impl.launch.knot.Knot.findEmbedddedGameProvider() and service loader records
 
 	String getEntrypoint();
-	Path getLaunchDirectory();
 	boolean isObfuscated();
 	boolean requiresUrlClassLoader();
 

src/test/java/net/fabricmc/loader/impl/discovery/GetNonFabricModsTest.java

@@ -63,7 +63,7 @@ public void setUp() {
 
 		loaderConstruction = Mockito.mockConstructionWithAnswer(FabricLoaderImpl.class, invocation -> loader);
 
-		discoverer = new ModDiscoverer(mock(), mock());
+		discoverer = new ModDiscoverer(provider, loader.isDevelopmentEnvironment(), loader.getEnvironmentType(), mock(), mock());
 		discoverer.addCandidateFinder(new MockCandidateFinder());
 	}
 
@@ -77,7 +77,12 @@ public void tearDown() {
 	 */
 	@Test
 	public void testGetNonFabricMods() throws ModResolutionException {
-		List<ModCandidateImpl> acceptedMods = discoverer.discoverMods(loader, new HashMap<String, Set<ModCandidateImpl>>());
+		ModDiscoveryInfo discoveryInfo = discoverer.discoverMods(new HashMap<String, Set<ModCandidateImpl>>());
+		List<ModCandidateImpl> acceptedMods = discoveryInfo.getFoundMods();
+
+		if (!discoveryInfo.launchable()) {
+			throw discoveryInfo.getException();
+		}
 
 		boolean foundDummyFabricMod = false;