Add cache directory API

src/main/java/net/fabricmc/loader/api/FabricLoader.java

@@ -211,6 +211,14 @@ static FabricLoader getInstance() {
 	@Deprecated
 	File getGameDirectory();
 
+	/**
+	 * Get the current directory for temporary files for a particular mod.
+	 *
+	 * @param modId The ID of the mod to get the cache directory for
+	 * @return the cache directory
+	 */
+	Path getCacheDir(String modId);
+
 	/**
 	 * Get the current directory for game configuration files.
 	 *

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

@@ -77,10 +77,14 @@ public final class FabricLoaderImpl extends net.fabricmc.loader.FabricLoader {
 	public static final String VERSION = "0.15.7";
 	public static final String MOD_ID = "fabricloader";
 
+	// Relative to game dir
+	private static final String MOD_CACHE_DIR = ".cache";
+	private static final String MOD_CONFIG_DIR = "config";
+
 	public static final String CACHE_DIR_NAME = ".fabric"; // relative to game dir
-	private static final String PROCESSED_MODS_DIR_NAME = "processedMods"; // relative to cache dir
-	public static final String REMAPPED_JARS_DIR_NAME = "remappedJars"; // relative to cache dir
-	private static final String TMP_DIR_NAME = "tmp"; // relative to cache dir
+	private static final String PROCESSED_MODS_DIR_NAME = "processedMods"; // relative to loader cache dir
+	public static final String REMAPPED_JARS_DIR_NAME = "remappedJars"; // relative to loader cache dir
+	private static final String TMP_DIR_NAME = "tmp"; // relative to loader cache dir
 
 	protected final Map<String, ModContainerImpl> modMap = new HashMap<>();
 	private List<ModCandidate> modCandidates;
@@ -99,6 +103,7 @@ public final class FabricLoaderImpl extends net.fabricmc.loader.FabricLoader {
 	private MappingResolver mappingResolver;
 	private GameProvider provider;
 	private Path gameDir;
+	private Path cacheDir;
 	private Path configDir;
 
 	private FabricLoaderImpl() { }
@@ -133,7 +138,8 @@ public void setGameProvider(GameProvider provider) {
 
 	private void setGameDir(Path gameDir) {
 		this.gameDir = gameDir;
-		this.configDir = gameDir.resolve("config");
+		this.cacheDir = gameDir.resolve(MOD_CACHE_DIR);
+		this.configDir = gameDir.resolve(MOD_CONFIG_DIR);
 	}
 
 	@Override
@@ -162,20 +168,32 @@ public File getGameDirectory() {
 		return getGameDir().toFile();
 	}
 
-	/**
-	 * @return The game instance's configuration directory.
-	 */
-	@Override
-	public Path getConfigDir() {
-		if (!Files.exists(configDir)) {
+	private Path ensureDirExists(Path path, String name) {
+		if (!Files.exists(path)) {
 			try {
-				Files.createDirectories(configDir);
+				Files.createDirectories(path);
 			} catch (IOException e) {
-				throw new RuntimeException("Creating config directory", e);
+				throw new RuntimeException("Creating " + name + " directory", e);
 			}
 		}
 
-		return configDir;
+		return path;
+	}
+
+	/**
+	 * @return The game instance's temporary file directory for a particular mod.
+	 */
+	@Override
+	public Path getCacheDir(String modId) {
+		return ensureDirExists(cacheDir.resolve(modId), "cache");
+	}
+
+	/**
+	 * @return The game instance's configuration directory.
+	 */
+	@Override
+	public Path getConfigDir() {
+		return ensureDirExists(configDir, "config");
 	}
 
 	@Override
@@ -230,16 +248,16 @@ private void setup() throws ModResolutionException {
 
 		dumpModList(modCandidates);
 
-		Path cacheDir = gameDir.resolve(CACHE_DIR_NAME);
-		Path outputdir = cacheDir.resolve(PROCESSED_MODS_DIR_NAME);
+		Path loaderCacheDir = gameDir.resolve(CACHE_DIR_NAME);
+		Path outputDir = loaderCacheDir.resolve(PROCESSED_MODS_DIR_NAME);
 
 		// runtime mod remapping
 
 		if (remapRegularMods) {
 			if (System.getProperty(SystemProperties.REMAP_CLASSPATH_FILE) == null) {
 				Log.warn(LogCategory.MOD_REMAP, "Runtime mod remapping disabled due to no fabric.remapClasspathFile being specified. You may need to update loom.");
 			} else {
-				RuntimeModRemapper.remap(modCandidates, cacheDir.resolve(TMP_DIR_NAME), outputdir);
+				RuntimeModRemapper.remap(modCandidates, loaderCacheDir.resolve(TMP_DIR_NAME), outputDir);
 			}
 		}
 
@@ -270,7 +288,7 @@ private void setup() throws ModResolutionException {
 		for (ModCandidate mod : modCandidates) {
 			if (!mod.hasPath() && !mod.isBuiltin()) {
 				try {
-					mod.setPaths(Collections.singletonList(mod.copyToDir(outputdir, false)));
+					mod.setPaths(Collections.singletonList(mod.copyToDir(outputDir, false)));
 				} catch (IOException e) {
 					throw new RuntimeException("Error extracting mod "+mod, e);
 				}