Introduce QIcon::fallbackSearchPaths()

... that will be used if an icon can't be found in the
current theme.

The Icon Theme Specification
https://standards.freedesktop.org/icon-theme-spec/latest/ar01s05.html
states that unthemed icons must be searched in the base directories,
i.e. /usr/share/icons, ... But in practice unthemed icons are
installed into /usr/share/pixmaps and this dir is not used as
a base dir for icon themes. So it's better to explicitly specify
fallback dirs to avoid needless access to the filesystem.

Also some KDE application install their own unthemed icons
(into /usr/share/<appname>/pics), that can't be found by
QIconLoader. With this change it would be possible for them
to specify dirs with unthemed icons and thus be displayed
correctly in non-KDE environments.

[ChangeLog][QtGui][QIcon] Added fallbackSearchPaths() that
will be used to find icons missing in the current icon theme.

Change-Id: I0dc55ba958b29356a3b0a2123d6b8faa24d4c91e
Task-number: QTBUG-33123
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

4 files changed, 13 insertions, 1 deletions

diff --git a/tests/auto/gui/image/qicon/fallback_icons/red.png b/tests/auto/gui/image/qicon/fallback_icons/red.png
new file mode 100644
index 0000000000..4a843e744f
--- /dev/null
+++ b/tests/auto/gui/image/qicon/fallback_icons/red.png
diff --git a/tests/auto/gui/image/qicon/qicon.pro b/tests/auto/gui/image/qicon/qicon.pro
index b3c60bf32b..c96f0555ad 100644
--- a/tests/auto/gui/image/qicon/qicon.pro
+++ b/tests/auto/gui/image/qicon/qicon.pro
@@ -6,4 +6,4 @@ qtHaveModule(widgets): QT += widgets
 SOURCES += tst_qicon.cpp
 RESOURCES = tst_qicon.qrc tst_qicon.cpp
 
-TESTDATA += icons/* second_icons/* *.png *.svg *.svgz
+TESTDATA += icons/* second_icons/* fallback_icons/* *.png *.svg *.svgz
diff --git a/tests/auto/gui/image/qicon/tst_qicon.cpp b/tests/auto/gui/image/qicon/tst_qicon.cpp
index bf8f7ade9e..b1a4e4312f 100644
--- a/tests/auto/gui/image/qicon/tst_qicon.cpp
+++ b/tests/auto/gui/image/qicon/tst_qicon.cpp
@@ -554,6 +554,11 @@ void tst_QIcon::fromTheme()
     QCOMPARE(firstSearchPath, QIcon::themeSearchPaths()[0]);
     QCOMPARE(secondSearchPath, QIcon::themeSearchPaths()[1]);
 
+    QString fallbackSearchPath = QStringLiteral(":/fallback_icons");
+    QIcon::setFallbackSearchPaths(QStringList() << fallbackSearchPath);
+    QCOMPARE(QIcon::fallbackSearchPaths().size(), 1);
+    QCOMPARE(fallbackSearchPath, QIcon::fallbackSearchPaths().at(0));
+
     QString themeName("testtheme");
     QIcon::setThemeName(themeName);
     QCOMPARE(QIcon::themeName(), themeName);
@@ -580,6 +585,12 @@ void tst_QIcon::fromTheme()
     QVERIFY(QIcon::hasThemeIcon("address-book-new"));
     QVERIFY(!abIcon.availableSizes().isEmpty());
 
+    // Test icon from fallback path
+    QIcon fallbackIcon = QIcon::fromTheme("red");
+    QVERIFY(!fallbackIcon.isNull());
+    QVERIFY(QIcon::hasThemeIcon("red"));
+    QCOMPARE(fallbackIcon.availableSizes().size(), 1);
+
     // Test non existing icon
     QIcon noIcon = QIcon::fromTheme("broken-icon");
     QVERIFY(noIcon.isNull());
diff --git a/tests/auto/gui/image/qicon/tst_qicon.qrc b/tests/auto/gui/image/qicon/tst_qicon.qrc
index 3c8fbba7c2..4b347ec88c 100644
--- a/tests/auto/gui/image/qicon/tst_qicon.qrc
+++ b/tests/auto/gui/image/qicon/tst_qicon.qrc
@@ -6,6 +6,7 @@
 <file>./icons/testtheme/16x16/actions/appointment-new.png</file>
 <file>./icons/testtheme/22x22/actions/appointment-new.png</file>
 <file>./second_icons/testtheme/32x32/actions/appointment-new.png</file>
+<file>./fallback_icons/red.png</file>
 <file>./icons/testtheme/index.theme</file>
 <file>./icons/testtheme/scalable/actions/svg-only.svg</file>
 <file>./icons/themeparent/16x16/actions/address-book-new.png</file>