From e3196484e15d0552ca44b8ab736e0ffb3e65cd77 Mon Sep 17 00:00:00 2001
From: Alessandro Pasotti <elpaso@itopen.it>
Date: Wed, 31 May 2023 09:56:25 +0200
Subject: [PATCH] Add more context to the legend filter expressions in layouts

Fix #53229
---
 .../auto_generated/qgslegendfilterbutton.sip.in   |  8 ++++++++
 src/gui/layout/qgslayoutlegendwidget.cpp          |  1 +
 src/gui/qgslegendfilterbutton.cpp                 | 15 ++++++++++++++-
 src/gui/qgslegendfilterbutton.h                   | 10 ++++++++++
 4 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/python/gui/auto_generated/qgslegendfilterbutton.sip.in b/python/gui/auto_generated/qgslegendfilterbutton.sip.in
index 2680d18924a..2459cf0f7c0 100644
--- a/python/gui/auto_generated/qgslegendfilterbutton.sip.in
+++ b/python/gui/auto_generated/qgslegendfilterbutton.sip.in
@@ -39,6 +39,14 @@ Returns the current text used as filter expression
 %Docstring
 Sets the current text used as filter expression.
 This will update the menu
+%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:: 3.32
 %End
 
     QgsVectorLayer *vectorLayer() const;
diff --git a/src/gui/layout/qgslayoutlegendwidget.cpp b/src/gui/layout/qgslayoutlegendwidget.cpp
index 6fd12f2f397..b10e8e2b35d 100644
--- a/src/gui/layout/qgslayoutlegendwidget.cpp
+++ b/src/gui/layout/qgslayoutlegendwidget.cpp
@@ -203,6 +203,7 @@ QgsLayoutLegendWidget::QgsLayoutLegendWidget( QgsLayoutItemLegend *legend, QgsMa
   mGroupFontButton->registerExpressionContextGenerator( this );
   mLayerFontButton->registerExpressionContextGenerator( this );
   mItemFontButton->registerExpressionContextGenerator( this );
+  mExpressionFilterButton->registerExpressionContextGenerator( this );
 
   mTitleFontButton->setLayer( coverageLayer() );
   mGroupFontButton->setLayer( coverageLayer() );
diff --git a/src/gui/qgslegendfilterbutton.cpp b/src/gui/qgslegendfilterbutton.cpp
index 7883ada7ed0..ac3a2ca68fe 100644
--- a/src/gui/qgslegendfilterbutton.cpp
+++ b/src/gui/qgslegendfilterbutton.cpp
@@ -20,6 +20,7 @@
 
 #include "qgsapplication.h"
 #include "qgsexpressionbuilderdialog.h"
+#include "qgsexpressioncontextutils.h"
 
 QgsLegendFilterButton::QgsLegendFilterButton( QWidget *parent )
   : QToolButton( parent )
@@ -58,7 +59,14 @@ void QgsLegendFilterButton::onToggle( bool checked )
 
 void QgsLegendFilterButton::onSetLegendFilterExpression()
 {
-  QgsExpressionBuilderDialog dlg( mLayer, mExpression );
+  QgsExpressionContext context;
+  if ( mExpressionContextGenerator )
+    context  = mExpressionContextGenerator->createExpressionContext();
+  else
+  {
+    context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer ) );
+  }
+  QgsExpressionBuilderDialog dlg( mLayer, mExpression, nullptr, QStringLiteral( "generic" ), context );
   if ( dlg.exec() )
   {
     setExpressionText( dlg.expressionText() );
@@ -79,6 +87,11 @@ void QgsLegendFilterButton::onSetLegendFilterExpression()
   }
 }
 
+void QgsLegendFilterButton::registerExpressionContextGenerator( QgsExpressionContextGenerator *generator )
+{
+  mExpressionContextGenerator = generator;
+}
+
 void QgsLegendFilterButton::onClearFilterExpression()
 {
   mClearExpressionAction->setEnabled( false );
diff --git a/src/gui/qgslegendfilterbutton.h b/src/gui/qgslegendfilterbutton.h
index d1838b0d9a6..10a1885a0e7 100644
--- a/src/gui/qgslegendfilterbutton.h
+++ b/src/gui/qgslegendfilterbutton.h
@@ -17,8 +17,10 @@
 
 #include <QToolButton>
 #include "qgis_gui.h"
+#include "qgsexpressioncontext.h"
 
 class QgsVectorLayer;
+class QgsExpressionContextGenerator;
 
 /**
  * \ingroup gui
@@ -52,6 +54,13 @@ class GUI_EXPORT QgsLegendFilterButton: public QToolButton
      */
     void setExpressionText( const QString &expression );
 
+    /**
+     * Register an expression context generator class that will be used to retrieve
+     * an expression context for the button when required.
+     * \since QGIS 3.32
+     */
+    void registerExpressionContextGenerator( QgsExpressionContextGenerator *generator );
+
     /**
      * Returns the current associated vectorLayer
      * May be NULLPTR
@@ -76,6 +85,7 @@ class GUI_EXPORT QgsLegendFilterButton: public QToolButton
     QAction *mSetExpressionAction = nullptr;
     QAction *mClearExpressionAction = nullptr;
     QString mExpression;
+    QgsExpressionContextGenerator *mExpressionContextGenerator = nullptr;
 
     void updateMenu();