Optimise loom configuration, saves 1.2 seconds in my testing. #319

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

@@ -235,10 +235,8 @@ public class LoomGradleExtension {
 	}
 
 	public File getNativesDirectory() {
-		Object customNativesDir = project.getProperties().get("fabric.loom.natives.dir");
+		if (project.hasProperty("fabric.loom.natives.dir")) {
-
+			return new File((String) project.property("fabric.loom.natives.dir"));
-		if (customNativesDir != null) {
-			return new File((String) customNativesDir);
 		}
 
 		File natives = new File(getUserCache(), "natives/" + getMinecraftProvider().getMinecraftVersion());

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

@@ -25,6 +25,8 @@
 package net.fabricmc.loom;
 
 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;
 
@@ -38,6 +40,7 @@ import net.fabricmc.loom.task.LoomTasks;
 
 public class LoomGradlePlugin implements Plugin<Project> {
 	public static boolean refreshDeps;
+	public static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
 
 	@Override
 	public void apply(Project project) {

src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java

@@ -32,16 +32,14 @@ import java.util.HashSet;
 import java.util.Set;
 import java.util.zip.ZipEntry;
 
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
 import com.google.gson.JsonObject;
 import org.zeroturnaround.zip.ZipUtil;
 import org.zeroturnaround.zip.transform.StringZipEntryTransformer;
 import org.zeroturnaround.zip.transform.ZipEntryTransformerEntry;
 
-public final class MixinRefmapHelper {
+import net.fabricmc.loom.LoomGradlePlugin;
-	private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
 
+public final class MixinRefmapHelper {
 	private MixinRefmapHelper() { }
 
 	public static boolean addRefmapName(String filename, String mixinVersion, Path outputPath) {
@@ -52,7 +50,7 @@ public final class MixinRefmapHelper {
 			return ZipUtil.transformEntries(output, mixinFilenames.stream().map((f) -> new ZipEntryTransformerEntry(f, new StringZipEntryTransformer("UTF-8") {
 				@Override
 				protected String transform(ZipEntry zipEntry, String input) throws IOException {
-					JsonObject json = GSON.fromJson(input, JsonObject.class);
+					JsonObject json = LoomGradlePlugin.GSON.fromJson(input, JsonObject.class);
 
 					if (!json.has("refmap")) {
 						json.addProperty("refmap", filename);
@@ -62,7 +60,7 @@ public final class MixinRefmapHelper {
 						json.addProperty("minVersion", mixinVersion);
 					}
 
-					return GSON.toJson(json);
+					return LoomGradlePlugin.GSON.toJson(json);
 				}
 			})).toArray(ZipEntryTransformerEntry[]::new));
 		} else {
@@ -78,7 +76,7 @@ public final class MixinRefmapHelper {
 			if (!entry.isDirectory() && entry.getName().endsWith(".json") && !entry.getName().contains("/") && !entry.getName().contains("\\")) {
 				// JSON file in root directory
 				try (InputStreamReader inputStreamReader = new InputStreamReader(stream)) {
-					JsonObject json = GSON.fromJson(inputStreamReader, JsonObject.class);
+					JsonObject json = LoomGradlePlugin.GSON.fromJson(inputStreamReader, JsonObject.class);
 
 					if (json != null) {
 						boolean hasMixins = json.has("mixins") && json.get("mixins").isJsonArray();

src/main/java/net/fabricmc/loom/build/ModCompileRemapper.java

@@ -52,6 +52,7 @@ import net.fabricmc.loom.configuration.processors.dependency.RemapData;
 import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.SourceRemapper;
 
+@SuppressWarnings("UnstableApiUsage")
 public class ModCompileRemapper {
 	public static void remapDependencies(Project project, String mappingsSuffix, LoomGradleExtension extension, SourceRemapper sourceRemapper) {
 		Logger logger = project.getLogger();
@@ -82,9 +83,7 @@ public class ModCompileRemapper {
 					continue;
 				}
 
-				File sources = findSources(dependencies, artifact);
+				ModDependencyInfo info = new ModDependencyInfo(group, name, version, classifierSuffix, artifact.getFile(), remappedConfig, remapData);
-
-				ModDependencyInfo info = new ModDependencyInfo(group, name, version, classifierSuffix, artifact.getFile(), sources, remappedConfig, remapData);
 
 				if (refreshDeps) {
 					info.forceRemap();
@@ -95,8 +94,14 @@ public class ModCompileRemapper {
 				String remappedLog = group + ":" + name + ":" + version + classifierSuffix + " (" + mappingsSuffix + ")";
 				project.getLogger().info(":providing " + remappedLog);
 
-				if (sources != null) {
+				File remappedSources = new File(info.getRemappedOutput().getAbsolutePath().replace(".jar", "-sources.jar"));
-					scheduleSourcesRemapping(project, sourceRemapper, info.sourcesFile, info.getRemappedNotation(), info.getRemappedOutput(), modStore);
+
+				if (!remappedSources.exists() || refreshDeps) {
+					File sources = findSources(dependencies, artifact);
+
+					if (sources != null) {
+						scheduleSourcesRemapping(project, sourceRemapper, sources, info.getRemappedNotation(), info.getRemappedOutput(), modStore);
+					}
 				}
 			}
 
@@ -145,8 +150,8 @@ public class ModCompileRemapper {
 	}
 
 	public static File findSources(DependencyHandler dependencies, ResolvedArtifact artifact) {
-		@SuppressWarnings("unchecked") ArtifactResolutionQuery query = dependencies.createArtifactResolutionQuery()//
+		@SuppressWarnings("unchecked") ArtifactResolutionQuery query = dependencies.createArtifactResolutionQuery()
-				.forComponents(artifact.getId().getComponentIdentifier())//
+				.forComponents(artifact.getId().getComponentIdentifier())
 				.withArtifacts(JvmLibrary.class, SourcesArtifact.class);
 
 		for (ComponentArtifactsResult result : query.execute().getResolvedComponents()) {

src/main/java/net/fabricmc/loom/build/NestedJars.java

@@ -36,8 +36,6 @@ import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.zip.ZipEntry;
 
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
 import org.apache.commons.io.FileUtils;
@@ -58,12 +56,11 @@ import org.zeroturnaround.zip.transform.StringZipEntryTransformer;
 import org.zeroturnaround.zip.transform.ZipEntryTransformerEntry;
 
 import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.task.RemapJarTask;
 import net.fabricmc.loom.util.Constants;
 
 public class NestedJars {
-	private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
-
 	public static boolean addNestedJars(Project project, Path modJarPath) {
 		List<File> containedJars = getContainedJars(project);
 
@@ -78,7 +75,7 @@ public class NestedJars {
 		return ZipUtil.transformEntries(modJar, single(new ZipEntryTransformerEntry("fabric.mod.json", new StringZipEntryTransformer() {
 			@Override
 			protected String transform(ZipEntry zipEntry, String input) {
-				JsonObject json = GSON.fromJson(input, JsonObject.class);
+				JsonObject json = LoomGradlePlugin.GSON.fromJson(input, JsonObject.class);
 				JsonArray nestedJars = json.getAsJsonArray("jars");
 
 				if (nestedJars == null || !json.has("jars")) {
@@ -93,7 +90,7 @@ public class NestedJars {
 
 				json.add("jars", nestedJars);
 
-				return GSON.toJson(json);
+				return LoomGradlePlugin.GSON.toJson(json);
 			}
 		})));
 	}
@@ -229,7 +226,7 @@ public class NestedJars {
 		custom.addProperty("fabric-loom:generated", true);
 		jsonObject.add("custom", custom);
 
-		return GSON.toJson(jsonObject);
+		return LoomGradlePlugin.GSON.toJson(jsonObject);
 	}
 
 	private static ZipEntryTransformerEntry[] single(ZipEntryTransformerEntry element) {

src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java

@@ -25,8 +25,6 @@
 package net.fabricmc.loom.configuration;
 
 import java.io.IOException;
-import java.util.Map;
-import java.util.Set;
 
 import org.gradle.api.Project;
 import org.gradle.api.Task;
@@ -198,18 +196,11 @@ public final class CompileConfiguration {
 				remapJarTask.dependsOn(jarTask);
 				project1.getTasks().getByName("build").dependsOn(remapJarTask);
 
-				Map<Project, Set<Task>> taskMap = project.getAllTasks(true);
+				project.getTasks().withType(RemapJarTask.class).forEach(task -> {
-
+					if (task.getAddNestedDependencies().getOrElse(false)) {
-				for (Map.Entry<Project, Set<Task>> entry : taskMap.entrySet()) {
+						NestedJars.getRequiredTasks(project1).forEach(task::dependsOn);
-					Set<Task> taskSet = entry.getValue();
-
-					for (Task task : taskSet) {
-						if (task instanceof RemapJarTask && ((RemapJarTask) task).getAddNestedDependencies().getOrElse(false)) {
-							//Run all the sub project remap jars tasks before the root projects jar, this is to allow us to include projects
-							NestedJars.getRequiredTasks(project1).forEach(task::dependsOn);
-						}
 					}
-				}
+				});
 
 				SourceRemapper remapper = null;
 				Task parentTask = project1.getTasks().getByName("build");

src/main/java/net/fabricmc/loom/configuration/DependencyProvider.java

@@ -100,6 +100,8 @@ public abstract class DependencyProvider {
 		final Dependency dependency;
 		final Configuration sourceConfiguration;
 
+		private String resolvedVersion = null;
+
 		public static DependencyInfo create(Project project, Dependency dependency, Configuration sourceConfiguration) {
 			if (dependency instanceof SelfResolvingDependency) {
 				return new FileDependencyInfo(project, (SelfResolvingDependency) dependency, sourceConfiguration);
@@ -119,13 +121,19 @@ public abstract class DependencyProvider {
 		}
 
 		public String getResolvedVersion() {
+			if (resolvedVersion != null) {
+				return resolvedVersion;
+			}
+
 			for (ResolvedDependency rd : sourceConfiguration.getResolvedConfiguration().getFirstLevelModuleDependencies()) {
 				if (rd.getModuleGroup().equals(dependency.getGroup()) && rd.getModuleName().equals(dependency.getName())) {
-					return rd.getModuleVersion();
+					resolvedVersion = rd.getModuleVersion();
+					return resolvedVersion;
 				}
 			}
 
-			return dependency.getVersion();
+			resolvedVersion = dependency.getVersion();
+			return resolvedVersion;
 		}
 
 		public Configuration getSourceConfiguration() {

src/main/java/net/fabricmc/loom/configuration/LoomDependencyManager.java

@@ -87,7 +87,7 @@ public class LoomDependencyManager {
 
 		MappingsProvider mappingsProvider = null;
 
-		project.getLogger().lifecycle(":setting up loom dependencies");
+		project.getLogger().info(":setting up loom dependencies");
 		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
 		Map<String, ProviderList> providerListMap = new HashMap<>();
 		List<ProviderList> targetProviders = new ArrayList<>();

src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java

@@ -41,8 +41,6 @@ import java.util.jar.JarFile;
 import java.util.stream.Collectors;
 import java.util.zip.ZipEntry;
 
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
 import com.google.gson.JsonObject;
 import org.apache.commons.io.IOUtils;
 import org.gradle.api.Project;
@@ -56,6 +54,7 @@ import net.fabricmc.accesswidener.AccessWidenerReader;
 import net.fabricmc.accesswidener.AccessWidenerRemapper;
 import net.fabricmc.accesswidener.AccessWidenerWriter;
 import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.configuration.RemappedConfigurationEntry;
 import net.fabricmc.loom.configuration.processors.dependency.ModDependencyInfo;
 import net.fabricmc.loom.configuration.providers.mappings.MappingsProvider;
@@ -67,8 +66,6 @@ import net.fabricmc.tinyremapper.OutputConsumerPath;
 import net.fabricmc.tinyremapper.TinyRemapper;
 
 public class ModProcessor {
-	public static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
-
 	public static void processMods(Project project, List<ModDependencyInfo> processList) throws IOException {
 		if (processList.stream().noneMatch(ModDependencyInfo::requiresRemapping)) {
 			return;
@@ -104,9 +101,9 @@ public class ModProcessor {
 		ZipUtil.transformEntries(file, new ZipEntryTransformerEntry[] {(new ZipEntryTransformerEntry("fabric.mod.json", new StringZipEntryTransformer() {
 			@Override
 			protected String transform(ZipEntry zipEntry, String input) {
-				JsonObject json = GSON.fromJson(input, JsonObject.class);
+				JsonObject json = LoomGradlePlugin.GSON.fromJson(input, JsonObject.class);
 				json.remove("jars");
-				return GSON.toJson(json);
+				return LoomGradlePlugin.GSON.toJson(json);
 			}
 		}))});
 	}
@@ -236,7 +233,7 @@ public class ModProcessor {
 				}
 			}
 
-			return GSON.fromJson(jsonStr, JsonObject.class);
+			return LoomGradlePlugin.GSON.fromJson(jsonStr, JsonObject.class);
 		} catch (IOException e) {
 			e.printStackTrace();
 		}

src/main/java/net/fabricmc/loom/configuration/processors/dependency/ModDependencyInfo.java

@@ -37,7 +37,7 @@ import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.IOUtils;
 import org.gradle.api.artifacts.Configuration;
 
-import net.fabricmc.loom.configuration.mods.ModProcessor;
+import net.fabricmc.loom.LoomGradlePlugin;
 
 public class ModDependencyInfo {
 	private final String group;
@@ -45,20 +45,18 @@ public class ModDependencyInfo {
 	public final String version;
 	public final String classifier;
 	public final File inputFile;
-	public final File sourcesFile;
 	public final Configuration targetConfig;
 
 	public final RemapData remapData;
 
 	private boolean forceRemap = false;
 
-	public ModDependencyInfo(String group, String name, String version, String classifier, File inputFile, File sourcesFile, Configuration targetConfig, RemapData remapData) {
+	public ModDependencyInfo(String group, String name, String version, String classifier, File inputFile, Configuration targetConfig, RemapData remapData) {
 		this.group = group;
 		this.name = name;
 		this.version = version;
 		this.classifier = classifier;
 		this.inputFile = inputFile;
-		this.sourcesFile = sourcesFile;
 		this.targetConfig = targetConfig;
 		this.remapData = remapData;
 	}
@@ -149,7 +147,7 @@ public class ModDependencyInfo {
 			}
 
 			try (InputStream inputStream = jarFile.getInputStream(modJsonEntry)) {
-				JsonObject json = ModProcessor.GSON.fromJson(new InputStreamReader(inputStream), JsonObject.class);
+				JsonObject json = LoomGradlePlugin.GSON.fromJson(new InputStreamReader(inputStream), JsonObject.class);
 
 				if (!json.has("accessWidener")) {
 					return null;

src/main/java/net/fabricmc/loom/configuration/providers/MinecraftProvider.java

@@ -31,22 +31,24 @@ import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.util.Optional;
 import java.util.function.Consumer;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 import java.util.zip.ZipError;
 
 import com.google.common.io.Files;
-import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import org.gradle.api.GradleException;
 import org.gradle.api.Project;
 import org.gradle.api.logging.Logger;
 
+import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.configuration.DependencyProvider;
 import net.fabricmc.loom.configuration.providers.minecraft.ManifestVersion;
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftLibraryProvider;
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftVersionInfo;
 import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.DownloadUtil;
-import net.fabricmc.loom.util.StaticPathWatcher;
+import net.fabricmc.loom.util.HashedDownloadUtil;
 import net.fabricmc.stitch.merge.JarMerger;
 
 public class MinecraftProvider extends DependencyProvider {
@@ -59,8 +61,7 @@ public class MinecraftProvider extends DependencyProvider {
 	private File minecraftClientJar;
 	private File minecraftServerJar;
 	private File minecraftMergedJar;
-
+	private File versionManifestJson;
-	Gson gson = new Gson();
 
 	public MinecraftProvider(Project project) {
 		super(project);
@@ -77,7 +78,7 @@ public class MinecraftProvider extends DependencyProvider {
 		downloadMcJson(offline);
 
 		try (FileReader reader = new FileReader(minecraftJson)) {
-			versionInfo = gson.fromJson(reader, MinecraftVersionInfo.class);
+			versionInfo = LoomGradlePlugin.GSON.fromJson(reader, MinecraftVersionInfo.class);
 		}
 
 		// Add Loom as an annotation processor
@@ -117,29 +118,30 @@ public class MinecraftProvider extends DependencyProvider {
 		minecraftClientJar = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-client.jar");
 		minecraftServerJar = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-server.jar");
 		minecraftMergedJar = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-merged.jar");
+		versionManifestJson = new File(getExtension().getUserCache(), "version_manifest.json");
 	}
 
 	private void downloadMcJson(boolean offline) throws IOException {
-		File manifests = new File(getExtension().getUserCache(), "version_manifest.json");
+		if (getExtension().isShareCaches() && !getExtension().isRootProject() && versionManifestJson.exists() && !isRefreshDeps()) {
-
-		if (getExtension().isShareCaches() && !getExtension().isRootProject() && manifests.exists() && !isRefreshDeps()) {
 			return;
 		}
 
-		if (offline) {
+		if (!offline && !isRefreshDeps() && hasRecentValidManifest()) {
-			if (manifests.exists()) {
+			// We have a recent valid manifest file, so do nothing
+		} else if (offline) {
+			if (versionManifestJson.exists()) {
 				// If there is the manifests already we'll presume that's good enough
 				getProject().getLogger().debug("Found version manifests, presuming up-to-date");
 			} else {
 				// If we don't have the manifests then there's nothing more we can do
-				throw new GradleException("Version manifests not found at " + manifests.getAbsolutePath());
+				throw new GradleException("Version manifests not found at " + versionManifestJson.getAbsolutePath());
 			}
 		} else {
 			getProject().getLogger().debug("Downloading version manifests");
-			DownloadUtil.downloadIfChanged(new URL(Constants.VERSION_MANIFESTS), manifests, getProject().getLogger());
+			DownloadUtil.downloadIfChanged(new URL(Constants.VERSION_MANIFESTS), versionManifestJson, getProject().getLogger());
 		}
 
-		String versionManifest = Files.asCharSource(manifests, StandardCharsets.UTF_8).read();
+		String versionManifest = Files.asCharSource(versionManifestJson, StandardCharsets.UTF_8).read();
 		ManifestVersion mcManifest = new GsonBuilder().create().fromJson(versionManifest, ManifestVersion.class);
 
 		Optional<ManifestVersion.Versions> optionalVersion = Optional.empty();
@@ -166,9 +168,18 @@ public class MinecraftProvider extends DependencyProvider {
 					throw new GradleException("Minecraft " + minecraftVersion + " manifest not found at " + minecraftJson.getAbsolutePath());
 				}
 			} else {
-				if (StaticPathWatcher.INSTANCE.hasFileChanged(minecraftJson.toPath()) || isRefreshDeps()) {
+				getProject().getLogger().debug("Downloading Minecraft {} manifest", minecraftVersion);
-					getProject().getLogger().debug("Downloading Minecraft {} manifest", minecraftVersion);
+
-					DownloadUtil.downloadIfChanged(new URL(optionalVersion.get().url), minecraftJson, getProject().getLogger());
+				String url = optionalVersion.get().url;
+				// Find the sha1 of the json from the url, return true if it matches the local json
+				Pattern sha1Pattern = Pattern.compile("\\b[0-9a-f]{5,40}\\b");
+				Matcher matcher = sha1Pattern.matcher(url);
+
+				if (matcher.find()) {
+					HashedDownloadUtil.downloadIfInvalid(new URL(url), minecraftJson, matcher.group(), getProject().getLogger(), true);
+				} else {
+					// Use the etag if no hash found from url
+					DownloadUtil.downloadIfChanged(new URL(url), minecraftJson, getProject().getLogger());
 				}
 			}
 		} else {
@@ -176,13 +187,37 @@ public class MinecraftProvider extends DependencyProvider {
 		}
 	}
 
+	private boolean hasRecentValidManifest() throws IOException {
+		if (getExtension().customManifest != null) {
+			return false;
+		}
+
+		if (!versionManifestJson.exists() || !minecraftJson.exists()) {
+			return false;
+		}
+
+		if (versionManifestJson.lastModified() > System.currentTimeMillis() - 24 * 3_600_000) {
+			// Version manifest hasn't been modified in 24 hours, time to get a new one.
+			return false;
+		}
+
+		ManifestVersion manifest = new GsonBuilder().create().fromJson(Files.asCharSource(versionManifestJson, StandardCharsets.UTF_8).read(), ManifestVersion.class);
+		Optional<ManifestVersion.Versions> version = manifest.versions.stream().filter(versions -> versions.id.equalsIgnoreCase(minecraftVersion)).findFirst();
+
+		// fail if the expected mc version was not found, will download the file again.
+		return version.isPresent();
+	}
+
 	private void downloadJars(Logger logger) throws IOException {
 		if (getExtension().isShareCaches() && !getExtension().isRootProject() && minecraftClientJar.exists() && minecraftServerJar.exists() && !isRefreshDeps()) {
 			return;
 		}
 
-		DownloadUtil.downloadIfChanged(new URL(versionInfo.downloads.get("client").url), minecraftClientJar, logger);
+		MinecraftVersionInfo.Downloads client = versionInfo.downloads.get("client");
-		DownloadUtil.downloadIfChanged(new URL(versionInfo.downloads.get("server").url), minecraftServerJar, logger);
+		MinecraftVersionInfo.Downloads server = versionInfo.downloads.get("server");
+
+		HashedDownloadUtil.downloadIfInvalid(new URL(client.url), minecraftClientJar, client.sha1, logger, false);
+		HashedDownloadUtil.downloadIfInvalid(new URL(server.url), minecraftServerJar, server.sha1, logger, false);
 	}
 
 	private void mergeJars(Logger logger) throws IOException {

src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProvider.java

@@ -97,7 +97,7 @@ public class MappingsProvider extends DependencyProvider {
 	public void provide(DependencyInfo dependency, Consumer<Runnable> postPopulationScheduler) throws Exception {
 		MinecraftProvider minecraftProvider = getDependencyManager().getProvider(MinecraftProvider.class);
 
-		getProject().getLogger().lifecycle(":setting up mappings (" + dependency.getDependency().getName() + " " + dependency.getResolvedVersion() + ")");
+		getProject().getLogger().info(":setting up mappings (" + dependency.getDependency().getName() + " " + dependency.getResolvedVersion() + ")");
 
 		String version = dependency.getResolvedVersion();
 		File mappingsJar = dependency.resolveFile().orElseThrow(() -> new RuntimeException("Could not find yarn mappings: " + dependency));
@@ -105,6 +105,8 @@ public class MappingsProvider extends DependencyProvider {
 		this.mappingsName = StringUtils.removeSuffix(dependency.getDependency().getGroup() + "." + dependency.getDependency().getName(), "-unmerged");
 		this.minecraftVersion = minecraftProvider.getMinecraftVersion();
 
+		boolean isV2;
+
 		// Only do this for official yarn, there isn't really a way we can get the mc version for all mappings
 		if (dependency.getDependency().getGroup() != null && dependency.getDependency().getGroup().equals("net.fabricmc") && dependency.getDependency().getName().equals("yarn") && dependency.getDependency().getVersion() != null) {
 			String yarnVersion = dependency.getDependency().getVersion();
@@ -114,9 +116,13 @@ public class MappingsProvider extends DependencyProvider {
 			if (!yarnMinecraftVersion.equalsIgnoreCase(minecraftVersion)) {
 				throw new RuntimeException(String.format("Minecraft Version (%s) does not match yarn's minecraft version (%s)", minecraftVersion, yarnMinecraftVersion));
 			}
+
+			// We can save reading the zip file + header by checking the file name
+			isV2 = mappingsJar.getName().endsWith("-v2.jar");
+		} else {
+			isV2 = doesJarContainV2Mappings(mappingsJar.toPath());
 		}
 
-		boolean isV2 = doesJarContainV2Mappings(mappingsJar.toPath());
 		this.mappingsVersion = version + (isV2 ? "-v2" : "");
 
 		initFiles();

src/main/java/net/fabricmc/loom/task/AbstractRunTask.java

@@ -45,9 +45,6 @@ public abstract class AbstractRunTask extends JavaExec {
 		super();
 		setGroup("fabric");
 		this.configProvider = config;
-
-		classpath(getProject().getConfigurations().getByName("runtimeClasspath"));
-		classpath(this.getProject().getExtensions().getByType(LoomGradleExtension.class).getUnmappedModCollection());
 	}
 
 	@Override
@@ -56,6 +53,9 @@ public abstract class AbstractRunTask extends JavaExec {
 			config = configProvider.apply(getProject());
 		}
 
+		classpath(getProject().getConfigurations().getByName("runtimeClasspath"));
+		classpath(this.getProject().getExtensions().getByType(LoomGradleExtension.class).getUnmappedModCollection());
+
 		List<String> argsSplit = new ArrayList<>();
 		String[] args = config.programArgs.split(" ");
 		int partPos = -1;

src/main/java/net/fabricmc/loom/util/Checksum.java

@@ -37,21 +37,14 @@ public class Checksum {
 	private static final Logger log = Logging.getLogger(Checksum.class);
 
 	public static boolean equals(File file, String checksum) {
-		if (file == null) {
+		if (file == null || !file.exists()) {
 			return false;
 		}
 
 		try {
-			//noinspection deprecation
 			HashCode hash = Files.asByteSource(file).hash(Hashing.sha1());
-			StringBuilder builder = new StringBuilder();
+			log.debug("Checksum check: '" + hash.toString() + "' == '" + checksum + "'?");
-
+			return hash.toString().equals(checksum);
-			for (Byte hashBytes : hash.asBytes()) {
-				builder.append(Integer.toString((hashBytes & 0xFF) + 0x100, 16).substring(1));
-			}
-
-			log.debug("Checksum check: '" + builder.toString() + "' == '" + checksum + "'?");
-			return builder.toString().equals(checksum);
 		} catch (IOException e) {
 			e.printStackTrace();
 		}

src/main/java/net/fabricmc/loom/util/DownloadUtil.java

@@ -192,7 +192,7 @@ public class DownloadUtil {
 	 * @param bytes The number of bytes
 	 * @return The given number of bytes formatted to kilobytes, megabytes or gigabytes if appropriate
 	 */
-	private static String toNiceSize(long bytes) {
+	public static String toNiceSize(long bytes) {
 		if (bytes < 1024) {
 			return bytes + " B";
 		} else if (bytes < 1024 * 1024) {

src/main/java/net/fabricmc/loom/util/HashedDownloadUtil.java

@@ -0,0 +1,136 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2016, 2017, 2018 FabricMC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.util;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+
+import javax.annotation.Nullable;
+
+import com.google.common.hash.Hashing;
+import com.google.common.io.Files;
+import org.apache.commons.io.FileUtils;
+import org.gradle.api.logging.Logger;
+
+import net.fabricmc.loom.LoomGradlePlugin;
+
+public class HashedDownloadUtil {
+	public static void downloadIfInvalid(URL from, File to, String expectedHash, Logger logger, boolean quiet) throws IOException {
+		if (LoomGradlePlugin.refreshDeps) {
+			delete(to);
+		}
+
+		if (to.exists()) {
+			String sha1 = getSha1(to, logger);
+
+			if (expectedHash.equals(sha1)) {
+				// The hash in the sha1 file matches
+				return;
+			}
+		}
+
+		HttpURLConnection connection = (HttpURLConnection) from.openConnection();
+		connection.setRequestProperty("Accept-Encoding", "gzip");
+		connection.connect();
+
+		int code = connection.getResponseCode();
+
+		if ((code < 200 || code > 299) && code != HttpURLConnection.HTTP_NOT_MODIFIED) {
+			//Didn't get what we expected
+			throw new IOException(connection.getResponseMessage() + " for " + from);
+		}
+
+		long contentLength = connection.getContentLengthLong();
+
+		if (!quiet && contentLength >= 0) {
+			logger.info("'{}' Changed, downloading {}", to, DownloadUtil.toNiceSize(contentLength));
+		}
+
+		try { // Try download to the output
+			FileUtils.copyInputStreamToFile(connection.getInputStream(), to);
+		} catch (IOException e) {
+			delete(to); // Probably isn't good if it fails to copy/save
+			throw e;
+		}
+
+		if (!Checksum.equals(to, expectedHash)) {
+			String actualHash = Files.asByteSource(to).hash(Hashing.sha1()).toString();
+			delete(to);
+
+			throw new IOException(String.format("Downloaded file from %s to %s and got unexpected hash of %s expected %s", from, to, actualHash, expectedHash));
+		}
+
+		saveSha1(to, expectedHash, logger);
+	}
+
+	private static File getSha1File(File file) {
+		return new File(file.getAbsoluteFile().getParentFile(), file.getName() + ".sha1");
+	}
+
+	@Nullable
+	private static String getSha1(File to, Logger logger) {
+		File sha1File = getSha1File(to);
+
+		if (!sha1File.exists()) {
+			return null;
+		}
+
+		try {
+			return Files.asCharSource(sha1File, StandardCharsets.UTF_8).read();
+		} catch (IOException e) {
+			logger.warn("Error reading sha1 file '{}'.", sha1File);
+			return null;
+		}
+	}
+
+	private static void saveSha1(File to, String sha1, Logger logger) {
+		File sha1File = getSha1File(to);
+
+		try {
+			if (!sha1File.exists()) {
+				sha1File.createNewFile();
+			}
+
+			Files.asCharSink(sha1File, StandardCharsets.UTF_8).write(sha1);
+		} catch (IOException e) {
+			logger.warn("Error saving sha1 file '{}'.", sha1File, e);
+		}
+	}
+
+	public static void delete(File file) {
+		if (file.exists()) {
+			file.delete();
+		}
+
+		File sha1File = getSha1File(file);
+
+		if (sha1File.exists()) {
+			sha1File.delete();
+		}
+	}
+}