JENKINS-10599 Publish over ssh with flatten creates empty directory

Only create the target directory when the first file is copied.

src/main/java/jenkins/plugins/publish_over/BPTransfer.java

@@ -185,20 +185,24 @@ public void transferFile(final BPClient client, final FilePath filePath) throws
         private final BPBuildInfo buildInfo;
         private final BPClient client;
         private final Set<String> flattenedFileNames = new LinkedHashSet<String>();
+        private boolean flattenResetCompleted;
         private String previousPath;
         private String relativeRemoteSubDirectory;
 
         DirectoryMaker(final BPBuildInfo buildInfo, final BPClient client) throws IOException {
             this.buildInfo = buildInfo;
             this.client = client;
-            if (flatten) {
-                resetToSubDirectory();
-            }
         }
 
         public void changeAndMakeDirs(final FilePath filePath) throws IOException, InterruptedException {
-            if (flatten)
+            if (flatten) {
                 assertNotDuplicateFileName(filePath);
+                if (!flattenResetCompleted) {
+                    // Only create target directory when there is a file to store
+                    resetToSubDirectory();
+                    flattenResetCompleted = true;
+                }
+            }
             final String relPath = buildInfo.getRelativePath(filePath, removePrefix);
             if (LOG.isDebugEnabled())
                 LOG.debug(Messages.log_pathToFile(filePath.getName(), relPath));

src/test/java/jenkins/plugins/publish_over/BPTransferTest.java

@@ -148,6 +148,13 @@ private void assertSingleFileInRoot(final String filename, final String pattern)
         assertTransfer(transfer, expectedFileCount);
     }
 
+    @Test public void testNoFiles() throws Exception {
+        final BPTransfer transfer = new BPTransfer("*.log", "", "", false, false);
+        // Should not change to/create initial directory on zero file transfer
+        final int expectedFileCount = 0;
+        assertTransfer(transfer, expectedFileCount);
+    }
+
     @Test public void testEnvVarInPattern() throws Exception {
         final RandomFile toTransfer = new RandomFile(baseDir.getRoot(), "hello_123.txt");
         final BPTransfer transfer = new BPTransfer("hello_${BUILD_NUMBER}.*", "", "", false, false);
@@ -299,6 +306,14 @@ private void assertCreateDirectories(final RandomFile srcFile, final String remo
         assertTransfer(transfer, 2);
     }
 
+    @Test public void testCreateNoFilesWithDirectories() throws Exception {
+        final String remoteDir = "remote/root";
+        final BPTransfer transfer = new BPTransfer("**/*", remoteDir, "", false, false);
+
+        // Should not change to/create initial directory on zero file transfer
+        assertTransfer(transfer, 0);
+    }
+
     @Test public void testFlatten() throws Exception {
         final String srcPath1 = "bit/of/a/trek/to";
         final String srcPath2 = "file/somewhere";
@@ -317,6 +332,14 @@ private void assertCreateDirectories(final RandomFile srcFile, final String remo
         assertTransfer(transfer, 2);
     }
 
+    @Test public void testFlattenWithNoFiles() throws Exception {
+        final String remoteDir = "remote/root";
+        final BPTransfer transfer = new BPTransfer("**/*", remoteDir, "", false, true);
+
+        // Should not change to/create initial directory on zero file transfer
+        assertTransfer(transfer, 0);
+    }
+
     @Test(expected = BapPublisherException.class)
     public void testFlattenThrowsExceptionIfTwoFilesHaveSameName() throws Exception {
         final String srcPath1 = "bit/of/a/trek/to";
@@ -353,6 +376,15 @@ public void testFlattenThrowsExceptionIfTwoFilesHaveSameName() throws Exception
         assertTransfer(transfer, 2);
     }
 
+    @Test public void testRemovePrefixNoFiles() throws Exception {
+        final String prefix = "gonna/remove";
+
+        final BPTransfer transfer = new BPTransfer("**/*", "", prefix, false, false);
+
+        // Should not change to/create initial directory on zero file transfer
+        assertTransfer(transfer, 0);
+    }
+
     @Test public void testRemovePrefixTrailingSlash() throws Exception {
         final String prefix = "gonna/remove/";
         final String srcPath1 = "but/not/this";