Improve support for saving QImage to QSaveFile

When saving to a QIODevice, QImage and QImageWriter will automatically
deduct the file format from the filename if it determines that the
device is a QFile. That did not work for a QSaveFile device. Fix by
using the common ancestor, QFileDevice, in the implementation.

Fixes: QTBUG-89022
Change-Id: Ie01d80df4f29ca0d4ff30bf7e1b77605293c070e
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit f0510d5bd2f1ed1dc76f6f89fb24566045d9ade7)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 60 insertions, 5 deletions

diff --git a/src/gui/image/qimagewriter.cpp b/src/gui/image/qimagewriter.cpp
index 519a222db1..668d366208 100644
--- a/src/gui/image/qimagewriter.cpp
+++ b/src/gui/image/qimagewriter.cpp
@@ -153,7 +153,7 @@ static QImageIOHandler *createWriteHandlerHelper(QIODevice *device,
         // if there's no format, see if \a device is a file, and if so, find
         // the file suffix and find support for that format among our plugins.
         // this allows plugins to override our built-in handlers.
-        if (QFile *file = qobject_cast<QFile *>(device)) {
+        if (QFileDevice *file = qobject_cast<QFileDevice *>(device)) {
             if (!(suffix = QFileInfo(file->fileName()).suffix().toLower().toLatin1()).isEmpty()) {
 #ifndef QT_NO_IMAGEFORMATPLUGIN
                 const int index = keyMap.key(QString::fromLatin1(suffix), -1);
@@ -428,17 +428,17 @@ void QImageWriter::setFileName(const QString &fileName)
 }
 
 /*!
-    If the currently assigned device is a QFile, or if setFileName()
+    If the currently assigned device is a file, or if setFileName()
     has been called, this function returns the name of the file
     QImageWriter writes to. Otherwise (i.e., if no device has been
-    assigned or the device is not a QFile), an empty QString is
+    assigned or the device is not a file), an empty QString is
     returned.
 
     \sa setFileName(), setDevice()
 */
 QString QImageWriter::fileName() const
 {
-    QFile *file = qobject_cast<QFile *>(d->device);
+    QFileDevice *file = qobject_cast<QFileDevice *>(d->device);
     return file ? file->fileName() : QString();
 }
 
@@ -719,7 +719,7 @@ bool QImageWriter::write(const QImage &image)
 
     if (!d->handler->write(img))
         return false;
-    if (QFile *file = qobject_cast<QFile *>(d->device))
+    if (QFileDevice *file = qobject_cast<QFileDevice *>(d->device))
         file->flush();
     return true;
 }
diff --git a/tests/auto/gui/image/qimagewriter/tst_qimagewriter.cpp b/tests/auto/gui/image/qimagewriter/tst_qimagewriter.cpp
index 49a4504d2a..924174e358 100644
--- a/tests/auto/gui/image/qimagewriter/tst_qimagewriter.cpp
+++ b/tests/auto/gui/image/qimagewriter/tst_qimagewriter.cpp
@@ -36,6 +36,7 @@
 #include <QSet>
 #include <QTemporaryDir>
 #include <QTemporaryFile>
+#include <QSaveFile>
 
 #ifdef Q_OS_UNIX // for geteuid()
 # include <sys/types.h>
@@ -75,6 +76,7 @@ private slots:
     void saveWithNoFormat();
 
     void saveToTemporaryFile();
+    void saveToSaveFile();
 
     void writeEmpty();
 
@@ -530,6 +532,59 @@ void tst_QImageWriter::saveToTemporaryFile()
     }
 }
 
+void tst_QImageWriter::saveToSaveFile()
+{
+    QImage image(prefix + "kollada.png");
+    QVERIFY(!image.isNull());
+
+    {
+        // Check canWrite
+        QImageWriter writer;
+        QSaveFile file(writePrefix + "savefile0.png");
+        writer.setDevice(&file);
+        QVERIFY2(writer.canWrite(), qPrintable(writer.errorString()));
+    }
+
+    QString fileName1(writePrefix + "savefile1.garble");
+    {
+        // Check failing canWrite
+        QVERIFY(!QFileInfo(fileName1).exists());
+        QImageWriter writer;
+        QSaveFile file(fileName1);
+        writer.setDevice(&file);
+        QVERIFY(!writer.canWrite());
+        QCOMPARE(writer.error(), QImageWriter::UnsupportedFormatError);
+    }
+    QVERIFY(!QFileInfo(fileName1).exists());
+
+    QString fileName2(writePrefix + "savefile2.png");
+    {
+        QImageWriter writer;
+        QSaveFile file(fileName2);
+        writer.setDevice(&file);
+        QCOMPARE(writer.fileName(), fileName2);
+        QVERIFY2(writer.write(image), qPrintable(writer.errorString()));
+        QVERIFY(file.commit());
+    }
+    {
+        QImage tmp;
+        QVERIFY(tmp.load(fileName2, "PNG"));
+        QCOMPARE(tmp, image);
+    }
+
+    QString fileName3(writePrefix + "savefile3.png");
+    {
+        QSaveFile file(fileName3);
+        QVERIFY(image.save(&file));
+        QVERIFY(file.commit());
+    }
+    {
+        QImage tmp;
+        QVERIFY(tmp.load(fileName3, "PNG"));
+        QCOMPARE(tmp, image);
+    }
+}
+
 void tst_QImageWriter::writeEmpty()
 {
     // check writing a null QImage errors gracefully