cease loading the same mappings file a million times

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

@@ -0,0 +1,53 @@
+/*
+ * 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 net.fabricmc.mappings.*;
+import net.fabricmc.tinyremapper.IMappingProvider;
+import net.fabricmc.tinyremapper.MemberInstance;
+
+public class TinyRemapperMappingsHelper {
+	private TinyRemapperMappingsHelper() {
+
+	}
+
+	public static IMappingProvider create(Mappings mappings, String from, String to) {
+		return (classMap, fieldMap, methodMap) -> {
+			for (ClassEntry entry : mappings.getClassEntries()) {
+				classMap.put(entry.get(from), entry.get(to));
+			}
+
+			for (FieldEntry entry : mappings.getFieldEntries()) {
+				EntryTriple fromTriple = entry.get(from);
+				fieldMap.put(fromTriple.getOwner() + "/" + MemberInstance.getFieldId(fromTriple.getName(), fromTriple.getDesc()), entry.get(to).getName());
+			}
+
+			for (MethodEntry entry : mappings.getMethodEntries()) {
+				EntryTriple fromTriple = entry.get(from);
+				methodMap.put(fromTriple.getOwner() + "/" + MemberInstance.getMethodId(fromTriple.getName(), fromTriple.getDesc()), entry.get(to).getName());
+			}
+		};
+	}
+}