chore: allow outputting to folder if its empty

brut.apktool/apktool-lib/src/main/java/brut/androlib/ApkDecoder.java

@@ -59,7 +59,10 @@ public ApkDecoder(File apkFile, Config config) {
 
     public void decode(File outDir) throws AndrolibException {
         if (!mConfig.isForced() && outDir.exists()) {
-            throw new OutDirExistsException(outDir.getPath());
+            File[] outDirFiles = outDir.isDirectory() ? outDir.listFiles() : null;
+            if (!outDir.isDirectory() || outDirFiles == null || outDirFiles.length > 0) {
+                throw new OutDirExistsException(outDir.getPath());
+            }
         }
         if (!mApkFile.isFile() || !mApkFile.canRead()) {
             throw new InFileNotFoundException(mApkFile.getPath());

brut.apktool/apktool-lib/src/test/java/brut/androlib/OutDirExistsTest.java

@@ -0,0 +1,94 @@
+/*
+ *  Copyright (C) 2010 Ryszard Wiśniewski <brut.alll@gmail.com>
+ *  Copyright (C) 2010 Connor Tumbleson <connor.tumbleson@gmail.com>
+ *
+ *  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
+ *
+ *       https://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 brut.androlib;
+
+import brut.androlib.exceptions.OutDirExistsException;
+
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+
+import org.junit.*;
+import static org.junit.Assert.*;
+
+public class OutDirExistsTest extends BaseTest {
+    private static final String TEST_APK = "issue2701.apk";
+
+    private File testApk;
+    private File outDir;
+
+    @BeforeClass
+    public static void beforeClass() throws Exception {
+        copyResourceDir(OutDirExistsTest.class, "issue2701", sTmpDir);
+    }
+
+    @Before
+    public void setUp() throws Exception {
+        testApk = new File(sTmpDir, TEST_APK);
+        outDir = new File(sTmpDir, TEST_APK + ".out_" + System.nanoTime());
+    }
+
+    @Test
+    public void decodeToNonExistentDir() throws Exception {
+        new ApkDecoder(testApk, sConfig).decode(outDir);
+
+        assertTrue(outDir.isDirectory());
+        assertTrue(new File(outDir, "AndroidManifest.xml").isFile());
+    }
+
+    @Test
+    public void decodeToExistingEmptyDir() throws Exception {
+        assertTrue(outDir.mkdirs());
+
+        new ApkDecoder(testApk, sConfig).decode(outDir);
+
+        assertTrue(new File(outDir, "AndroidManifest.xml").isFile());
+    }
+
+    @Test(expected = OutDirExistsException.class)
+    public void decodeToExistingNonEmptyDirThrows() throws Exception {
+        assertTrue(outDir.mkdirs());
+        touchFile(new File(outDir, "dummy.txt"));
+
+        new ApkDecoder(testApk, sConfig).decode(outDir);
+    }
+
+    @Test
+    public void decodeToExistingNonEmptyDirWithForce() throws Exception {
+        assertTrue(outDir.mkdirs());
+        touchFile(new File(outDir, "dummy.txt"));
+
+        sConfig.setForced(true);
+        new ApkDecoder(testApk, sConfig).decode(outDir);
+
+        assertTrue(new File(outDir, "AndroidManifest.xml").isFile());
+    }
+
+    @Test(expected = OutDirExistsException.class)
+    public void decodeToFileInsteadOfDirThrows() throws Exception {
+        File fileOutDir = new File(sTmpDir, "not_a_dir_" + System.nanoTime());
+        touchFile(fileOutDir);
+
+        new ApkDecoder(testApk, sConfig).decode(fileOutDir);
+    }
+
+    private static void touchFile(File file) throws IOException {
+        try (FileWriter fw = new FileWriter(file)) {
+            fw.write("content");
+        }
+    }
+}