Android: fix and document QStandardPaths behavior on different versions

Partially revert e1440dd7bc1a5da9a536f88b9733d04ec8fa6e61 for Android
versions below 11 which could take advantage of the manifest
flag android:requestLegacyExternalStorage. And for other newer versions
avoid returning them while adding a note to the docs about this
behavior.

Fixes: QTBUG-108013
Fixes: QTBUG-104892
Task-number: QTBUG-81860
Change-Id: I10851c20e2831bddaa329164c941e2ae71f0a497
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>
Reviewed-by: Rami Potinkara <rami.potinkara@qt.io>
(cherry picked from commit 81a748efb742092f5a0a1c33b8340478e52cc79f)
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

2 files changed, 81 insertions, 15 deletions

diff --git a/src/corelib/io/qstandardpaths.cpp b/src/corelib/io/qstandardpaths.cpp
index ec8e6899e4..a20c50e096 100644
--- a/src/corelib/io/qstandardpaths.cpp
+++ b/src/corelib/io/qstandardpaths.cpp
@@ -250,7 +250,7 @@ using namespace Qt::StringLiterals;
          \li "<APPROOT>/files"
          \li "<APPROOT>/Documents/Desktop"
     \row \li DocumentsLocation
-         \li "<USER>/Documents", "<USER>/<APPNAME>/Documents"
+         \li "<USER>/Documents" [*], "<USER>/<APPNAME>/Documents"
          \li "<APPROOT>/Documents"
     \row \li FontsLocation
          \li "/system/fonts" (not writable)
@@ -259,13 +259,13 @@ using namespace Qt::StringLiterals;
          \li not supported (directory not readable)
          \li not supported
     \row \li MusicLocation
-         \li "<USER>/Music", "<USER>/<APPNAME>/Music"
+         \li "<USER>/Music" [*], "<USER>/<APPNAME>/Music"
          \li "<APPROOT>/Documents/Music"
     \row \li MoviesLocation
-         \li "<USER>/Movies", "<USER>/<APPNAME>/Movies"
+         \li "<USER>/Movies" [*], "<USER>/<APPNAME>/Movies"
          \li "<APPROOT>/Documents/Movies"
     \row \li PicturesLocation
-         \li "<USER>/Pictures", "<USER>/<APPNAME>/Pictures"
+         \li "<USER>/Pictures" [*], "<USER>/<APPNAME>/Pictures"
          \li "<APPROOT>/Documents/Pictures", "assets-library://"
     \row \li TempLocation
          \li "<APPROOT>/cache"
@@ -280,7 +280,7 @@ using namespace Qt::StringLiterals;
          \li "<APPROOT>/cache", "<USER>/<APPNAME>/cache"
          \li "<APPROOT>/Library/Caches"
     \row \li GenericDataLocation
-         \li "<USER>"
+         \li "<USER>" [*] or "<USER>/<APPNAME>/files"
          \li "<APPROOT>/Library/Application Support"
     \row \li RuntimeLocation
          \li "<APPROOT>/cache"
@@ -292,7 +292,7 @@ using namespace Qt::StringLiterals;
          \li "<APPROOT>/files/settings" (there is no shared settings)
          \li "<APPROOT>/Library/Preferences"
     \row \li DownloadLocation
-         \li "<USER>/Downloads", "<USER>/<APPNAME>/Downloads"
+         \li "<USER>/Downloads" [*], "<USER>/<APPNAME>/Downloads"
          \li "<APPROOT>/Documents/Downloads"
     \row \li GenericCacheLocation
          \li "<APPROOT>/cache" (there is no shared cache)
@@ -328,6 +328,11 @@ using namespace Qt::StringLiterals;
 
     \note On Android, reading/writing to GenericDataLocation needs the READ_EXTERNAL_STORAGE/WRITE_EXTERNAL_STORAGE permission granted.
 
+    \note [*] On Android 11 and above, public directories are no longer directly accessible
+    in scoped storage mode. Thus, paths of the form \c "<USER>/DirName" are not returned.
+    Instead, you can use \l QFileDialog which uses the Storage Access Framework (SAF)
+    to access such directories.
+
     \note On iOS, if you do pass \c {QStandardPaths::standardLocations(QStandardPaths::PicturesLocation).last()}
         as argument to \l{QFileDialog::setDirectory()},
         a native image picker dialog will be used for accessing the user's photo album.
diff --git a/src/corelib/io/qstandardpaths_android.cpp b/src/corelib/io/qstandardpaths_android.cpp
index efc3661e23..a911087c9c 100644
--- a/src/corelib/io/qstandardpaths_android.cpp
+++ b/src/corelib/io/qstandardpaths_android.cpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2021 The Qt Company Ltd.
+// Copyright (C) 2023 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
 #include "qstandardpaths.h"
@@ -12,6 +12,9 @@
 
 QT_BEGIN_NAMESPACE
 
+Q_DECLARE_JNI_CLASS(Environment, "android/os/Environment");
+Q_DECLARE_JNI_TYPE(File, "Ljava/io/File;");
+
 using namespace QNativeInterface;
 using namespace Qt::StringLiterals;
 
@@ -34,6 +37,48 @@ static inline QString getAbsolutePath(const QJniObject &file)
 }
 
 /*
+ * The root of the external storage
+ *
+ */
+static QString getExternalStorageDirectory()
+{
+    QString &path = (*androidDirCache)[QStringLiteral("EXT_ROOT")];
+    if (!path.isEmpty())
+        return path;
+
+    QJniObject file = QJniObject::callStaticMethod<QtJniTypes::File>("android/os/Environment",
+                                                                     "getExternalStorageDirectory");
+    if (!file.isValid())
+        return QString();
+
+    return (path = getAbsolutePath(file));
+}
+
+/*
+ * Locations where applications can place user files shared by all apps (public).
+ * E.g., /storage/Music
+ */
+static QString getExternalStoragePublicDirectory(const char *directoryField)
+{
+    QString &path = (*androidDirCache)[QLatin1String(directoryField)];
+    if (!path.isEmpty())
+        return path;
+
+    QJniObject dirField = QJniObject::getStaticField<jstring>("android/os/Environment",
+                                                              directoryField);
+    if (!dirField.isValid())
+        return QString();
+
+    QJniObject file = QJniObject::callStaticMethod<QtJniTypes::File>("android/os/Environment",
+                                                            "getExternalStoragePublicDirectory",
+                                                            dirField.object<jstring>());
+    if (!file.isValid())
+        return QString();
+
+    return (path = getAbsolutePath(file));
+}
+
+/*
  * Locations where applications can place persistent files it owns.
  * E.g., /storage/org.app/Music
  */
@@ -132,25 +177,35 @@ static QString getFilesDir()
     return (path = getAbsolutePath(file));
 }
 
+static QString getSdkBasedExternalDir(const char *directoryField = nullptr)
+{
+    return (QNativeInterface::QAndroidApplication::sdkVersion() >= 30)
+            ? getExternalFilesDir(directoryField)
+            : getExternalStoragePublicDirectory(directoryField);
+}
+
 QString QStandardPaths::writableLocation(StandardLocation type)
 {
     switch (type) {
     case QStandardPaths::MusicLocation:
-        return getExternalFilesDir("DIRECTORY_MUSIC");
+        return getSdkBasedExternalDir("DIRECTORY_MUSIC");
     case QStandardPaths::MoviesLocation:
-        return getExternalFilesDir("DIRECTORY_MOVIES");
+        return getSdkBasedExternalDir("DIRECTORY_MOVIES");
     case QStandardPaths::PicturesLocation:
-        return getExternalFilesDir("DIRECTORY_PICTURES");
+        return getSdkBasedExternalDir("DIRECTORY_PICTURES");
     case QStandardPaths::DocumentsLocation:
-        return getExternalFilesDir("DIRECTORY_DOCUMENTS");
+        return getSdkBasedExternalDir("DIRECTORY_DOCUMENTS");
     case QStandardPaths::DownloadLocation:
-        return getExternalFilesDir("DIRECTORY_DOWNLOADS");
+        return getSdkBasedExternalDir("DIRECTORY_DOWNLOADS");
     case QStandardPaths::GenericConfigLocation:
     case QStandardPaths::ConfigLocation:
     case QStandardPaths::AppConfigLocation:
         return getFilesDir() + testDir() + "/settings"_L1;
     case QStandardPaths::GenericDataLocation:
-        return getExternalFilesDir() + testDir();
+    {
+        return QAndroidApplication::sdkVersion() >= 30 ?
+                getExternalFilesDir() + testDir() : getExternalStorageDirectory() + testDir();
+    }
     case QStandardPaths::AppDataLocation:
     case QStandardPaths::AppLocalDataLocation:
         return getFilesDir() + testDir();
@@ -178,8 +233,14 @@ QStringList QStandardPaths::standardLocations(StandardLocation type)
     QStringList locations;
 
     if (type == MusicLocation) {
-        locations << getExternalFilesDir("DIRECTORY_MUSIC")
-                  << getExternalFilesDir("DIRECTORY_PODCASTS")
+        locations << getExternalFilesDir("DIRECTORY_MUSIC");
+        // Place the public dirs before the app own dirs
+        if (QNativeInterface::QAndroidApplication::sdkVersion() < 30) {
+            locations << getExternalStoragePublicDirectory("DIRECTORY_PODCASTS")
+                      << getExternalStoragePublicDirectory("DIRECTORY_NOTIFICATIONS")
+                      << getExternalStoragePublicDirectory("DIRECTORY_ALARMS");
+        }
+        locations << getExternalFilesDir("DIRECTORY_PODCASTS")
                   << getExternalFilesDir("DIRECTORY_NOTIFICATIONS")
                   << getExternalFilesDir("DIRECTORY_ALARMS");
     } else if (type == MoviesLocation) {