Fix and test ClassInstance.addInputTags (#121)

* Fix and test ClassInstance.addInputTags

* Update fix

src/main/java/net/fabricmc/tinyremapper/ClassInstance.java

@@ -112,7 +112,7 @@ void addInputTags(InputTag[] tags) {
 
 				if (missingTags == 0) return;
 
-				newTags = Arrays.copyOf(tags, oldTags.length + missingTags);
+				newTags = Arrays.copyOf(oldTags, oldTags.length + missingTags);
 
 				for (InputTag newTag : tags) {
 					boolean found = false;
@@ -129,6 +129,8 @@ void addInputTags(InputTag[] tags) {
 						missingTags--;
 					}
 				}
+
+				assert missingTags == 0;
 			}
 		} while (!inputTagsUpdater.compareAndSet(this, oldTags, newTags));
 	}

src/test/java/net/fabricmc/tinyremapper/ClassInstanceTest.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2016, 2018, Player, asie
+ * Copyright (c) 2021, FabricMC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.fabricmc.tinyremapper;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
+
+public class ClassInstanceTest {
+	@Test
+	void addInputTags() {
+		InputTag tag1 = new InputTag();
+		InputTag tag2 = new InputTag();
+
+		ClassInstance classInstance = new ClassInstance(null, false, new InputTag[]{}, null, new byte[]{});
+		assertEquals(0, classInstance.getInputTags().length);
+
+		classInstance.addInputTags(new InputTag[]{tag1});
+		assertEquals(1, classInstance.getInputTags().length);
+		assertContains(tag1, classInstance.getInputTags());
+
+		classInstance.addInputTags(new InputTag[]{tag1});
+		assertEquals(1, classInstance.getInputTags().length);
+		assertContains(tag1, classInstance.getInputTags());
+
+		classInstance.addInputTags(new InputTag[]{tag2});
+		assertEquals(2, classInstance.getInputTags().length);
+		assertContains(tag1, classInstance.getInputTags());
+		assertContains(tag2, classInstance.getInputTags());
+	}
+
+	private static <T> void assertContains(T value, T[] array) {
+		for (T t : array) {
+			if (t == value) {
+				return;
+			}
+		}
+
+		fail("Array does not contain value: " + value);
+	}
+}