possibility to use a fallback chain as prefix

Summary:
if a framesvgitem has an array as prefix, like

FrameSvg {
 prefix: ["toolbutton-hover", "hover"]
}

it will use the first available prefix, so on themes that
have toolbutton-hover, that one will be used, old themes will
continue to use "hover" as prefix

Test Plan:
tested the calendar with breeze theme has breeze-widget style
toolbuttons, with olt themes as air, the old behavior is still
there, switching on the fly works

Reviewers: davidedmundson, #plasma

Subscribers: davidedmundson, broulik, plasma-devel, #frameworks

Tags: #plasma, #frameworks

Differential Revision: https://phabricator.kde.org/D4827

src/declarativeimports/core/framesvgitem.cpp

@@ -281,7 +281,6 @@ void FrameSvgItem::setImagePath(const QString &path)
 
     updateDevicePixelRatio();
     m_frameSvg->setImagePath(path);
-    m_frameSvg->setElementPrefix(m_prefix);
 
     if (implicitWidth() <= 0) {
         setImplicitWidth(m_frameSvg->marginSize(Plasma::Types::LeftMargin) + m_frameSvg->marginSize(Plasma::Types::RightMargin));
@@ -296,6 +295,8 @@ void FrameSvgItem::setImagePath(const QString &path)
     m_fixedMargins->update();
 
     if (isComponentComplete()) {
+        applyPrefixes();
+
         m_frameSvg->resizeFrame(QSizeF(width(), height()));
         m_textureChanged = true;
         update();
@@ -307,14 +308,22 @@ QString FrameSvgItem::imagePath() const
     return m_frameSvg->imagePath();
 }
 
-void FrameSvgItem::setPrefix(const QString &prefix)
+void FrameSvgItem::setPrefix(const QVariant &prefixes)
 {
-    if (m_prefix == prefix) {
+    QStringList prefixList;
+    //is this a simple string?
+    if (prefixes.canConvert<QString>()) {
+        prefixList << prefixes.toString();
+    } else if (prefixes.canConvert<QStringList>()) {
+        prefixList = prefixes.toStringList();
+    }
+
+    if (m_prefixes == prefixList) {
         return;
     }
 
-    m_frameSvg->setElementPrefix(prefix);
+    m_prefixes = prefixList;
-    m_prefix = prefix;
+    applyPrefixes();
 
     if (implicitWidth() <= 0) {
         setImplicitWidth(m_frameSvg->marginSize(Plasma::Types::LeftMargin) + m_frameSvg->marginSize(Plasma::Types::RightMargin));
@@ -335,9 +344,9 @@ void FrameSvgItem::setPrefix(const QString &prefix)
     }
 }
 
-QString FrameSvgItem::prefix() const
+QVariant FrameSvgItem::prefix() const
 {
-    return m_prefix;
+    return m_prefixes;
 }
 
 FrameSvgItemMargins *FrameSvgItem::margins() const
@@ -416,6 +425,9 @@ void FrameSvgItem::geometryChanged(const QRectF &newGeometry,
 
 void FrameSvgItem::doUpdate()
 {
+    //if the theme changed, the available prefix may have changed as well
+    applyPrefixes();
+
     if (implicitWidth() <= 0) {
         setImplicitWidth(m_frameSvg->marginSize(Plasma::Types::LeftMargin) + m_frameSvg->marginSize(Plasma::Types::RightMargin));
     }
@@ -445,7 +457,7 @@ Plasma::FrameSvg *FrameSvgItem::frameSvg() const
 QSGNode *FrameSvgItem::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *)
 {
     if (!window() || !m_frameSvg ||
-        (!m_frameSvg->hasElementPrefix(m_frameSvg->actualPrefix()) && !m_frameSvg->hasElementPrefix(m_prefix))) {
+        (!m_frameSvg->hasElementPrefix(m_frameSvg->actualPrefix()) && !m_frameSvg->hasElementPrefix(m_frameSvg->prefix()))) {
         delete oldNode;
         return nullptr;
     }
@@ -542,5 +554,26 @@ void FrameSvgItem::updateDevicePixelRatio()
     m_textureChanged = true;
 }
 
+void FrameSvgItem::applyPrefixes()
+{
+    if (m_prefixes.isEmpty() || m_frameSvg->imagePath().isEmpty()) {
+        return;
+    }
+
+    bool found = false;
+    for (const QString &prefix : m_prefixes) {
+        if (m_frameSvg->hasElementPrefix(prefix)) {
+            m_frameSvg->setElementPrefix(prefix);
+            found = true;
+            break;
+        }
+    }
+    if (!found) {
+        qWarning() << "The image" << m_frameSvg->imagePath() << "doesn't contain any of the prefixes" << m_prefixes;
+        //this setElementPrefix is done to keep the same behavior as before, when it was a simple string
+        m_frameSvg->setElementPrefix(m_prefixes.last());
+    }
+}
+
 } // Plasma namespace
 

src/declarativeimports/core/framesvgitem.h

@@ -119,8 +119,12 @@ class FrameSvgItem : public QQuickItem
      * prefix for the 9 piece svg, like "pushed" or "normal" for the button
      * see http://techbase.kde.org/Development/Tutorials/Plasma/ThemeDetails
      * for a list of paths and prefixes
+     * It can also be an array of strings, specifying a fallback chain in case
+     * the first element isn't found in the theme, eg ["toolbutton-normal", "normal"]
+     * so it's easy to keep backwards compatibility with old themes
+     * (Note: fallback chain is supported only @since 5.32)
      */
-    Q_PROPERTY(QString prefix READ prefix WRITE setPrefix NOTIFY prefixChanged)
+    Q_PROPERTY(QVariant prefix READ prefix WRITE setPrefix NOTIFY prefixChanged)
 
     /**
      * The margins of the frame, read only
@@ -185,8 +189,8 @@ public:
     void setImagePath(const QString &path);
     QString imagePath() const;
 
-    void setPrefix(const QString &prefix);
+    void setPrefix(const QVariant &prefix);
-    QString prefix() const;
+    QVariant prefix() const;
 
     void setEnabledBorders(const Plasma::FrameSvg::EnabledBorders borders);
     Plasma::FrameSvg::EnabledBorders enabledBorders() const;
@@ -234,10 +238,12 @@ private Q_SLOTS:
     void updateDevicePixelRatio();
 
 private:
+    void applyPrefixes();
+
     Plasma::FrameSvg *m_frameSvg;
     FrameSvgItemMargins *m_margins;
     FrameSvgItemMargins *m_fixedMargins;
-    QString m_prefix;
+    QStringList m_prefixes;
     bool m_textureChanged;
     bool m_sizeChanged;
     bool m_fastPath;

src/declarativeimports/plasmastyle/ToolButtonStyle.qml

@@ -231,7 +231,7 @@ QtQuickControlStyle.ButtonStyle {
                 id: surfaceNormal
                 anchors.fill: parent
                 imagePath: "widgets/button"
-                prefix: "normal"
+                prefix: style.flat ? ["toolbutton-hover", "normal"] : "normal"
 
                 enabledBorders: {
                     if (style.flat || !control.parent ||
@@ -288,7 +288,7 @@ QtQuickControlStyle.ButtonStyle {
                 id: surfacePressed
                 anchors.fill: parent
                 imagePath: "widgets/button"
-                prefix: "pressed"
+                prefix: style.flat ? ["toolbutton-pressed", "pressed"] : "pressed"
                 enabledBorders: surfaceNormal.enabledBorders
                 opacity: 0
             }