Android: fix Android assets handler not listing dirs with only sub dirs

It looks like AAssetDir_getNextFileName is not enough.
Directories that contain only other directories (no files)
were not listed.

On the other hand, AAssetManager_openDir() will always return a
pointer to initialized object (even if the specified directory does not
exists), so we can't just leave only it here.

Using FolderIterator as a last resort. This approach should not be too
time consuming.

As part of this fix, add some unit tests to cover/ensure assets
listing/iterating works as expected.

Fixes: QTBUG-107627
Pick-to: 6.4 6.2 5.15
Change-Id: Id375fe8f99f4ca3f8cad4756f783ffafe5c074df
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

src/plugins/platforms/android/qandroidassetsfileenginehandler.cpp

@@ -108,6 +108,8 @@ public:
     FolderIterator(const QString &path)
         : m_path(path)
     {
+        // Note that empty dirs in the assets dir before the build are not going to be
+        // included in the final apk, so no empty folders should expected to be listed.
         QJniObject files = QJniObject::callStaticObjectMethod(QtAndroid::applicationClass(),
                                                                             "listAssetContent",
                                                                             "(Landroid/content/res/AssetManager;Ljava/lang/String;)[Ljava/lang/String;",
@@ -350,8 +352,13 @@ public:
         } else {
             auto *assetDir = AAssetManager_openDir(m_assetManager, m_fileName.toUtf8());
             if (assetDir) {
-                if (AAssetDir_getNextFileName(assetDir))
+                if (AAssetDir_getNextFileName(assetDir)
+                        || (!FolderIterator::fromCache(m_fileName, false)->empty())) {
+                    // If AAssetDir_getNextFileName is not valid, it still can be a directory that
+                    // contains only other directories (no files). FolderIterator will not be called
+                    // on the directory containing files so it should not be too time consuming now.
                     m_assetInfo->type = AssetItem::Type::Folder;
+                }
                 AAssetDir_close(assetDir);
             }
         }

tests/auto/corelib/platform/android/testdata/assets/top_level_dir/file_in_top_dir.txt

@@ -0,0 +1 @@
+FooBar

tests/auto/corelib/platform/android/testdata/assets/top_level_dir/sub_dir/file_in_sub_dir.txt

@@ -0,0 +1 @@
+FooBar

tests/auto/corelib/platform/android/testdata/assets/top_level_dir/sub_dir/sub_dir_2/sub_dir_3/file_in_sub_dir_3.txt

@@ -0,0 +1 @@
+FooBar

tests/auto/corelib/platform/android/tst_android.cpp

@@ -7,9 +7,11 @@
 #include <QGuiApplication>
 #include <QtCore/qnativeinterface.h>
 #include <QtCore/qjniobject.h>
+#include <QtCore/qdiriterator.h>
 #include <QScreen>
 #include <qpa/qplatformscreen.h>
 #include <qpa/qplatformnativeinterface.h>
+#include <QtCore/qdiriterator.h>
 
 class tst_Android : public QObject
 {
@@ -17,6 +19,7 @@ Q_OBJECT
 private slots:
     void assetsRead();
     void assetsNotWritable();
+    void assetsIterating();
     void testAndroidSdkVersion();
     void testAndroidActivity();
     void testRunOnAndroidMainThread();
@@ -46,6 +49,27 @@ void tst_Android::assetsNotWritable()
     QVERIFY(!file.open(QIODevice::Append));
 }
 
+void tst_Android::assetsIterating()
+{
+    QStringList assets = {"assets:/top_level_dir/file_in_top_dir.txt",
+                          "assets:/top_level_dir/sub_dir",
+                          "assets:/top_level_dir/sub_dir/file_in_sub_dir.txt",
+                          "assets:/top_level_dir/sub_dir/sub_dir_2",
+                          "assets:/top_level_dir/sub_dir/sub_dir_2/sub_dir_3",
+                          "assets:/top_level_dir/sub_dir/sub_dir_2/sub_dir_3/file_in_sub_dir_3.txt"};
+
+    // Note that we have an "assets:/top_level_dir/sub_dir/empty_sub_dir" in the test's
+    // assets physical directory, but empty folders are not packaged in the built apk,
+    // so it's expected to not have such folder be listed in the assets on runtime
+
+    QDirIterator it("assets:/top_level_dir", QDirIterator::Subdirectories);
+    QStringList iteratorAssets;
+     while (it.hasNext())
+         iteratorAssets.append(it.next());
+
+     QVERIFY(assets == iteratorAssets);
+}
+
 void tst_Android::testAndroidSdkVersion()
 {
     QVERIFY(QNativeInterface::QAndroidApplication::sdkVersion() > 0);