Qt 5.7.1 (qt-everywhere-opensource-src-5.7.1)

availableSizes() always empty for SVG with filename & extension,
but work for SVG with filename (without extension)

qtbase-opensource-src-5.7.1+dfsg/src/gui/image/qicon.cpp:1209

QIcon QIcon::fromTheme(const QString &name, const QIcon &fallback)
{
    QIcon icon = fromTheme(name);

    if (icon.isNull() || *icon.availableSizes().isEmpty()*)
        return fallback;

    return icon;
}

Probably it's happened because QSvgIconEngine has no "virtual_hook(int id, void *data)" unlike QPixmapIconEngine

so, in next code (QIcon::addFile)
use 'filename + extension' --> QSvgIconEngine and QIcon::fromTheme do not work as expected
but if to variable fileName set only 'filename' --> QPixmapIconEngine --> SVG is Ok!

This is easy reproduced with breakpoint at line 1041
qt-everywhere-opensource-src-5.7.1/qtbase/src/gui//image/qicon.cpp

 QIcon::addFile(const QString &fileName, const QSize &size, Mode mode, State state)
{
    if (fileName.isEmpty())
        return;
    detach();
    if (!d) {

        QFileInfo info(fileName);
        QIconEngine *engine = iconEngineFromSuffix(fileName, info.suffix());
#ifndef QT_NO_MIMETYPE
        if (!engine)
            engine = iconEngineFromSuffix(fileName, QMimeDatabase().mimeTypeForFile(info).preferredSuffix());
#endif // !QT_NO_MIMETYPE
        d = new QIconPrivate;
        d->engine = engine ? engine : new QPixmapIconEngine;
    }

    d->engine->addFile(fileName, size, mode, state);

    // Check if a "@Nx" file exists and add it.
    QString atNxFileName = qt_findAtNxFile(fileName, qApp->devicePixelRatio());
    if (atNxFileName != fileName)
        d->engine->addFile(atNxFileName, size, mode, state);
}

At the same time icon.availableSizes().isEmpty() in QIcon::fromTheme has conflict with description:

Qt 5.7.1, quote from src/gui/image/qiconengine.cpp:143
\value AvailableSizesHook Allows to query the sizes of the contained pixmaps for pixmap-based engines. The \a data argument of the virtual_hook() function is a AvailableSizesArgument pointer that should be filled with icon sizes. Engines that work in terms of a scalable, vectorial format normally return an empty list.

Checked under Kubuntu 17.04, test project https://github.com/chipmunk-sm/qicontest

Affected to icon in .desktop file, so Dolphin and Application Menu do not show icon with full path and extensions.