Allow pushing more contextual information to QgsFontButton/QgsTextFormatWidget

e.g. follow the same approach as symbology and allow pushing message
bars, map canvases, and expression contexts to the widgets

python/gui/auto_generated/qgsfontbutton.sip.in

@@ -94,6 +94,25 @@ Sets a map ``canvas`` to associate with the widget. This allows the
 widget to fetch current settings from the map canvas, such as current scale.
 
 .. seealso:: :py:func:`mapCanvas`
+%End
+
+    void setMessageBar( QgsMessageBar *bar );
+%Docstring
+Sets the message ``bar`` associated with the widget. This allows the widget to push feedback messages
+to the appropriate message bar.
+
+.. seealso:: :py:func:`messageBar`
+
+.. versionadded:: 3.10
+%End
+
+    QgsMessageBar *messageBar() const;
+%Docstring
+Returns the message bar associated with the widget.
+
+.. seealso:: :py:func:`setMessageBar`
+
+.. versionadded:: 3.10
 %End
 
     QgsTextFormat textFormat() const;
@@ -112,6 +131,33 @@ This is only used when mode() is ModeQFont.
 .. seealso:: :py:func:`setCurrentFont`
 %End
 
+    QgsVectorLayer *layer() const;
+%Docstring
+Returns the layer associated with the widget.
+
+.. seealso:: :py:func:`setLayer`
+
+.. versionadded:: 3.10
+%End
+
+    void setLayer( QgsVectorLayer *layer );
+%Docstring
+Sets a ``layer`` to associate with the widget. This allows the
+widget to setup layer related settings within the text settings dialog,
+such as correctly populating data defined override buttons.
+
+.. seealso:: :py:func:`layer`
+
+.. versionadded:: 3.10
+%End
+
+    void registerExpressionContextGenerator( QgsExpressionContextGenerator *generator );
+%Docstring
+Register an expression context generator class that will be used to retrieve
+an expression context for the button when required.
+
+.. versionadded:: 3.10
+%End
 
   public slots:
 

python/gui/auto_generated/qgstextformatwidget.sip.in

@@ -34,13 +34,15 @@ of Labeling.
 %End
   public:
 
-    QgsTextFormatWidget( const QgsTextFormat &format = QgsTextFormat(), QgsMapCanvas *mapCanvas = 0, QWidget *parent /TransferThis/ = 0 );
+    QgsTextFormatWidget( const QgsTextFormat &format = QgsTextFormat(), QgsMapCanvas *mapCanvas = 0, QWidget *parent /TransferThis/ = 0,
+                         QgsVectorLayer *layer = 0 );
 %Docstring
 Constructor for QgsTextFormatWidget.
 
 :param format: initial formatting settings to show in widget
 :param mapCanvas: associated map canvas
 :param parent: parent widget
+:param layer: associated vector layer
 %End
 
     ~QgsTextFormatWidget();
@@ -99,7 +101,7 @@ Emitted when the text format defined by the widget changes
       Labeling,
     };
 
-    QgsTextFormatWidget( QgsMapCanvas *mapCanvas, QWidget *parent /TransferThis/, Mode mode );
+    QgsTextFormatWidget( QgsMapCanvas *mapCanvas, QWidget *parent /TransferThis/, Mode mode, QgsVectorLayer *layer = 0 );
 %Docstring
 Constructor for QgsTextFormatWidget.
 
@@ -187,7 +189,7 @@ a :py:class:`QgsTextFormat`, including shadow, background and buffer.
 %End
   public:
 
-    QgsTextFormatDialog( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = 0, QWidget *parent /TransferThis/ = 0, Qt::WindowFlags fl = QgsGuiUtils::ModalDialogFlags );
+    QgsTextFormatDialog( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = 0, QWidget *parent /TransferThis/ = 0, Qt::WindowFlags fl = QgsGuiUtils::ModalDialogFlags, QgsVectorLayer *layer = 0 );
 %Docstring
 Constructor for QgsTextFormatDialog.
 
@@ -195,11 +197,21 @@ Constructor for QgsTextFormatDialog.
 :param mapCanvas: optional associated map canvas
 :param parent: parent widget
 :param fl: window flags for dialog
+:param layer: associated vector layer
 %End
 
     QgsTextFormat format() const;
 %Docstring
 Returns the current formatting settings defined by the widget.
+%End
+
+    void setContext( const QgsSymbolWidgetContext &context );
+%Docstring
+Sets the ``context`` in which the widget is shown, e.g., the associated map canvas and expression contexts.
+
+.. seealso:: :py:func:`context`
+
+.. versionadded:: 3.10
 %End
 
     QDialogButtonBox *buttonBox() const;
@@ -229,18 +241,28 @@ a :py:class:`QgsTextFormat`, including shadow, background and buffer.
 %End
   public:
 
-    QgsTextFormatPanelWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = 0, QWidget *parent /TransferThis/ = 0 );
+    QgsTextFormatPanelWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = 0, QWidget *parent /TransferThis/ = 0, QgsVectorLayer *layer = 0 );
 %Docstring
 Constructor for QgsTextFormatPanelWidget.
 
 :param format: initial format settings to show in dialog
 :param mapCanvas: optional associated map canvas
 :param parent: parent widget
+:param layer: associated layer
 %End
 
     QgsTextFormat format() const;
 %Docstring
 Returns the current formatting settings defined by the widget.
+%End
+
+    void setContext( const QgsSymbolWidgetContext &context );
+%Docstring
+Sets the ``context`` in which the widget is shown, e.g., the associated map canvas and expression contexts.
+
+.. seealso:: :py:func:`context`
+
+.. versionadded:: 3.10
 %End
 
     virtual void setDockMode( bool dockMode );

src/gui/qgsfontbutton.cpp

@@ -26,6 +26,8 @@
 #include "qgsmenuheader.h"
 #include "qgsfontutils.h"
 #include "qgsapplication.h"
+#include "qgsexpressioncontextutils.h"
+#include "qgsvectorlayer.h"
 #include <QMenu>
 #include <QClipboard>
 #include <QDrag>
@@ -71,19 +73,34 @@ void QgsFontButton::showSettingsDialog()
   {
     case ModeTextRenderer:
     {
+      QgsExpressionContext context;
+      if ( mExpressionContextGenerator )
+        context  = mExpressionContextGenerator->createExpressionContext();
+      else
+      {
+        context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer.data() ) );
+      }
+
+      QgsSymbolWidgetContext symbolContext;
+      symbolContext.setExpressionContext( &context );
+      symbolContext.setMapCanvas( mMapCanvas );
+      symbolContext.setMessageBar( mMessageBar );
+
       QgsPanelWidget *panel = QgsPanelWidget::findParentPanel( this );
       if ( panel && panel->dockMode() )
       {
-        QgsTextFormatPanelWidget *formatWidget = new QgsTextFormatPanelWidget( mFormat, mMapCanvas, this );
+        QgsTextFormatPanelWidget *formatWidget = new QgsTextFormatPanelWidget( mFormat, mMapCanvas, this, mLayer.data() );
         formatWidget->setPanelTitle( mDialogTitle );
+        formatWidget->setContext( symbolContext );
 
         connect( formatWidget, &QgsTextFormatPanelWidget::widgetChanged, this, [ this, formatWidget ] { this->setTextFormat( formatWidget->format() ); } );
         panel->openPanel( formatWidget );
         return;
       }
 
-      QgsTextFormatDialog dialog( mFormat, mMapCanvas, this );
+      QgsTextFormatDialog dialog( mFormat, mMapCanvas, this, QgsGuiUtils::ModalDialogFlags, mLayer.data() );
       dialog.setWindowTitle( mDialogTitle );
+      dialog.setContext( symbolContext );
       if ( dialog.exec() )
       {
         setTextFormat( dialog.format() );
@@ -120,6 +137,16 @@ void QgsFontButton::setMapCanvas( QgsMapCanvas *mapCanvas )
   mMapCanvas = mapCanvas;
 }
 
+void QgsFontButton::setMessageBar( QgsMessageBar *bar )
+{
+  mMessageBar = bar;
+}
+
+QgsMessageBar *QgsFontButton::messageBar() const
+{
+  return mMessageBar;
+}
+
 void QgsFontButton::setTextFormat( const QgsTextFormat &format )
 {
   mFormat = format;
@@ -692,6 +719,21 @@ QFont QgsFontButton::currentFont() const
   return mFont;
 }
 
+QgsVectorLayer *QgsFontButton::layer() const
+{
+  return mLayer;
+}
+
+void QgsFontButton::setLayer( QgsVectorLayer *layer )
+{
+  mLayer = layer;
+}
+
+void QgsFontButton::registerExpressionContextGenerator( QgsExpressionContextGenerator *generator )
+{
+  mExpressionContextGenerator = generator;
+}
+
 void QgsFontButton::setCurrentFont( const QFont &font )
 {
   mFont = font;

src/gui/qgsfontbutton.h

@@ -21,7 +21,9 @@
 
 #include <QToolButton>
 
+class QgsExpressionContextGenerator;
 class QgsMapCanvas;
+class QgsMessageBar;
 
 /**
  * \ingroup gui
@@ -109,6 +111,21 @@ class GUI_EXPORT QgsFontButton : public QToolButton
      */
     void setMapCanvas( QgsMapCanvas *canvas );
 
+    /**
+     * Sets the message \a bar associated with the widget. This allows the widget to push feedback messages
+     * to the appropriate message bar.
+     * \see messageBar()
+     * \since QGIS 3.10
+     */
+    void setMessageBar( QgsMessageBar *bar );
+
+    /**
+     * Returns the message bar associated with the widget.
+     * \see setMessageBar()
+     * \since QGIS 3.10
+     */
+    QgsMessageBar *messageBar() const;
+
     /**
      * Returns the current text formatting set by the widget.
      * This is only used when mode() is ModeTextRenderer.
@@ -123,6 +140,28 @@ class GUI_EXPORT QgsFontButton : public QToolButton
      */
     QFont currentFont() const;
 
+    /**
+     * Returns the layer associated with the widget.
+     * \see setLayer()
+     * \since QGIS 3.10
+     */
+    QgsVectorLayer *layer() const;
+
+    /**
+     * Sets a \a layer to associate with the widget. This allows the
+     * widget to setup layer related settings within the text settings dialog,
+     * such as correctly populating data defined override buttons.
+     * \see layer()
+     * \since QGIS 3.10
+     */
+    void setLayer( QgsVectorLayer *layer );
+
+    /**
+     * Register an expression context generator class that will be used to retrieve
+     * an expression context for the button when required.
+     * \since QGIS 3.10
+     */
+    void registerExpressionContextGenerator( QgsExpressionContextGenerator *generator );
 
   public slots:
 
@@ -227,13 +266,18 @@ class GUI_EXPORT QgsFontButton : public QToolButton
     QFont mFont;
 
     QgsMapCanvas *mMapCanvas = nullptr;
+    QgsMessageBar *mMessageBar = nullptr;
 
     QPoint mDragStartPosition;
 
     QMenu *mMenu = nullptr;
 
+    QPointer< QgsVectorLayer > mLayer;
+
     QSize mIconSize;
 
+    QgsExpressionContextGenerator *mExpressionContextGenerator = nullptr;
+
     /**
      * Attempts to parse \a mimeData as a text format.
      * \returns TRUE if mime data could be intrepreted as a format

src/gui/qgslabelinggui.cpp

@@ -135,8 +135,7 @@ void QgsLabelingGui::updateCalloutWidget( QgsCallout *callout )
 }
 
 QgsLabelingGui::QgsLabelingGui( QgsVectorLayer *layer, QgsMapCanvas *mapCanvas, const QgsPalLayerSettings &layerSettings, QWidget *parent, QgsWkbTypes::GeometryType geomType )
-  : QgsTextFormatWidget( mapCanvas, parent, QgsTextFormatWidget::Labeling )
-  , mLayer( layer )
+  : QgsTextFormatWidget( mapCanvas, parent, QgsTextFormatWidget::Labeling, layer )
   , mGeomType( geomType )
   , mSettings( layerSettings )
   , mMode( NoLabels )

src/gui/qgstextformatwidget.cpp

@@ -31,22 +31,25 @@
 #include "qgsstylesavedialog.h"
 #include "qgsexpressioncontextutils.h"
 #include "qgsgui.h"
+#include "qgsvectorlayer.h"
 
 #include <QButtonGroup>
 #include <QMessageBox>
 
-QgsTextFormatWidget::QgsTextFormatWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas, QWidget *parent )
+QgsTextFormatWidget::QgsTextFormatWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas, QWidget *parent, QgsVectorLayer *layer )
   : QWidget( parent )
   , mMapCanvas( mapCanvas )
+  , mLayer( layer )
 {
   initWidget();
   setWidgetMode( Text );
   updateWidgetForFormat( format );
 }
 
-QgsTextFormatWidget::QgsTextFormatWidget( QgsMapCanvas *mapCanvas, QWidget *parent, Mode mode )
+QgsTextFormatWidget::QgsTextFormatWidget( QgsMapCanvas *mapCanvas, QWidget *parent, Mode mode, QgsVectorLayer *layer )
   : QWidget( parent )
   , mMapCanvas( mapCanvas )
+  , mLayer( layer )
   , mWidgetMode( mode )
 {
   initWidget();
@@ -941,6 +944,14 @@ void QgsTextFormatWidget::optionsStackedWidget_CurrentChanged( int indx )
 void QgsTextFormatWidget::setContext( const QgsSymbolWidgetContext &context )
 {
   mContext = context;
+
+  if ( mContext.expressionContext() )
+  {
+    mPreviewExpressionContext = *mContext.expressionContext();
+    if ( mLayer )
+      mPreviewExpressionContext.appendScope( QgsExpressionContextUtils::layerScope( mLayer ) );
+  }
+
   const auto symbolButtonWidgets = findChildren<QgsSymbolButton *>();
   for ( QgsSymbolButton *symbolWidget : symbolButtonWidgets )
   {
@@ -1660,6 +1671,9 @@ void QgsTextFormatWidget::enableDataDefinedAlignment( bool enable )
 
 QgsExpressionContext QgsTextFormatWidget::createExpressionContext() const
 {
+  if ( mContext.expressionContext() )
+    return *mContext.expressionContext();
+
   QgsExpressionContext expContext;
   expContext << QgsExpressionContextUtils::globalScope()
              << QgsExpressionContextUtils::projectScope( QgsProject::instance() )
@@ -1667,6 +1681,12 @@ QgsExpressionContext QgsTextFormatWidget::createExpressionContext() const
   if ( mMapCanvas )
     expContext << QgsExpressionContextUtils::mapSettingsScope( mMapCanvas->mapSettings() );
 
+  if ( mLayer )
+    expContext << QgsExpressionContextUtils::layerScope( mLayer );
+
+  //TODO - show actual value
+  expContext.setOriginalValueVariable( QVariant() );
+
   return expContext;
 }
 
@@ -1675,12 +1695,12 @@ QgsExpressionContext QgsTextFormatWidget::createExpressionContext() const
 // QgsTextFormatDialog
 //
 
-QgsTextFormatDialog::QgsTextFormatDialog( const QgsTextFormat &format, QgsMapCanvas *mapCanvas, QWidget *parent, Qt::WindowFlags fl )
+QgsTextFormatDialog::QgsTextFormatDialog( const QgsTextFormat &format, QgsMapCanvas *mapCanvas, QWidget *parent, Qt::WindowFlags fl, QgsVectorLayer *layer )
   : QDialog( parent, fl )
 {
   setWindowTitle( tr( "Text Settings" ) );
 
-  mFormatWidget = new QgsTextFormatWidget( format, mapCanvas, this );
+  mFormatWidget = new QgsTextFormatWidget( format, mapCanvas, this, layer );
   mFormatWidget->layout()->setContentsMargins( 0, 0, 0, 0 );
 
   QVBoxLayout *layout = new QVBoxLayout( this );
@@ -1701,13 +1721,18 @@ QgsTextFormat QgsTextFormatDialog::format() const
   return mFormatWidget->format();
 }
 
+void QgsTextFormatDialog::setContext( const QgsSymbolWidgetContext &context )
+{
+  mFormatWidget->setContext( context );
+}
+
 QDialogButtonBox *QgsTextFormatDialog::buttonBox() const
 {
   return mButtonBox;
 }
 
-QgsTextFormatPanelWidget::QgsTextFormatPanelWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas, QWidget *parent )
-  : QgsPanelWidgetWrapper( new QgsTextFormatWidget( format, mapCanvas ), parent )
+QgsTextFormatPanelWidget::QgsTextFormatPanelWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas, QWidget *parent, QgsVectorLayer *layer )
+  : QgsPanelWidgetWrapper( new QgsTextFormatWidget( format, mapCanvas, nullptr, layer ), parent )
 {
   mFormatWidget = qobject_cast< QgsTextFormatWidget * >( widget() );
   connect( mFormatWidget, &QgsTextFormatWidget::widgetChanged, this, &QgsPanelWidget::widgetChanged );
@@ -1718,6 +1743,11 @@ QgsTextFormat QgsTextFormatPanelWidget::format() const
   return mFormatWidget->format();
 }
 
+void QgsTextFormatPanelWidget::setContext( const QgsSymbolWidgetContext &context )
+{
+  mFormatWidget->setContext( context );
+}
+
 void QgsTextFormatPanelWidget::setDockMode( bool dockMode )
 {
   mFormatWidget->setDockMode( dockMode );

src/gui/qgstextformatwidget.h

@@ -59,8 +59,10 @@ class GUI_EXPORT QgsTextFormatWidget : public QWidget, public QgsExpressionConte
      * \param format initial formatting settings to show in widget
      * \param mapCanvas associated map canvas
      * \param parent parent widget
+     * \param layer associated vector layer
      */
-    QgsTextFormatWidget( const QgsTextFormat &format = QgsTextFormat(), QgsMapCanvas *mapCanvas = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr );
+    QgsTextFormatWidget( const QgsTextFormat &format = QgsTextFormat(), QgsMapCanvas *mapCanvas = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr,
+                         QgsVectorLayer *layer = nullptr );
 
     ~QgsTextFormatWidget() override;
 
@@ -117,7 +119,7 @@ class GUI_EXPORT QgsTextFormatWidget : public QWidget, public QgsExpressionConte
      * \param parent parent widget
      * \param mode widget mode
      */
-    QgsTextFormatWidget( QgsMapCanvas *mapCanvas, QWidget *parent SIP_TRANSFERTHIS, Mode mode );
+    QgsTextFormatWidget( QgsMapCanvas *mapCanvas, QWidget *parent SIP_TRANSFERTHIS, Mode mode, QgsVectorLayer *layer = nullptr );
 
     /**
      * Updates the widget's state to reflect the settings in a QgsTextFormat.
@@ -162,6 +164,8 @@ class GUI_EXPORT QgsTextFormatWidget : public QWidget, public QgsExpressionConte
     //! Context in which widget is shown
     QgsSymbolWidgetContext mContext;
 
+    //! Associated vector layer
+    QgsVectorLayer *mLayer = nullptr;
   protected slots:
 
     //! Updates line placement options to reflect current state of widget
@@ -202,6 +206,7 @@ class GUI_EXPORT QgsTextFormatWidget : public QWidget, public QgsExpressionConte
     bool mDockMode;
 
     bool mLoadSvgParams = false;
+    QgsExpressionContext mPreviewExpressionContext;
 
     void initWidget();
     void setWidgetMode( Mode mode );
@@ -279,14 +284,22 @@ class GUI_EXPORT QgsTextFormatDialog : public QDialog
      * \param mapCanvas optional associated map canvas
      * \param parent parent widget
      * \param fl window flags for dialog
+     * \param layer associated vector layer
      */
-    QgsTextFormatDialog( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr, Qt::WindowFlags fl = QgsGuiUtils::ModalDialogFlags );
+    QgsTextFormatDialog( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr, Qt::WindowFlags fl = QgsGuiUtils::ModalDialogFlags, QgsVectorLayer *layer = nullptr );
 
     /**
      * Returns the current formatting settings defined by the widget.
      */
     QgsTextFormat format() const;
 
+    /**
+     * Sets the \a context in which the widget is shown, e.g., the associated map canvas and expression contexts.
+     * \see context()
+     * \since QGIS 3.10
+     */
+    void setContext( const QgsSymbolWidgetContext &context );
+
     /**
      * Returns a reference to the dialog's button box.
      * \since QGIS 3.10
@@ -322,14 +335,22 @@ class GUI_EXPORT QgsTextFormatPanelWidget : public QgsPanelWidgetWrapper
      * \param format initial format settings to show in dialog
      * \param mapCanvas optional associated map canvas
      * \param parent parent widget
+     * \param layer associated layer
      */
-    QgsTextFormatPanelWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr );
+    QgsTextFormatPanelWidget( const QgsTextFormat &format, QgsMapCanvas *mapCanvas = nullptr, QWidget *parent SIP_TRANSFERTHIS = nullptr, QgsVectorLayer *layer = nullptr );
 
     /**
      * Returns the current formatting settings defined by the widget.
      */
     QgsTextFormat format() const;
 
+    /**
+     * Sets the \a context in which the widget is shown, e.g., the associated map canvas and expression contexts.
+     * \see context()
+     * \since QGIS 3.10
+     */
+    void setContext( const QgsSymbolWidgetContext &context );
+
     void setDockMode( bool dockMode ) override;
 
   private: