From 70fa078410ffdfaa8b5fb7e60ba4a1e090740b4d Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Mon, 24 May 2021 13:18:34 +1000
Subject: [PATCH] Make QgsMapCanvas a QgsExpressionContextGenerator

(cherry picked from commit 79338d130607d6c36c5d4625eb394463c2909d61)
---
 python/gui/auto_generated/qgsmapcanvas.sip.in |  8 +++--
 src/gui/qgsmapcanvas.cpp                      | 35 ++++++++++---------
 src/gui/qgsmapcanvas.h                        |  6 ++--
 3 files changed, 29 insertions(+), 20 deletions(-)

diff --git a/python/gui/auto_generated/qgsmapcanvas.sip.in b/python/gui/auto_generated/qgsmapcanvas.sip.in
index dc8d9ffc14a1..6ebb3bfa6770 100644
--- a/python/gui/auto_generated/qgsmapcanvas.sip.in
+++ b/python/gui/auto_generated/qgsmapcanvas.sip.in
@@ -21,7 +21,8 @@
 
 
 
-class QgsMapCanvas : QGraphicsView
+
+class QgsMapCanvas : QGraphicsView, QgsExpressionContextGenerator
 {
 %Docstring
 Map canvas is a class for displaying all GIS data types on a canvas.
@@ -694,7 +695,7 @@ overrides for expression evaluation for the map canvas render.
 %End
 
 
-    QgsExpressionContextScope *defaultExpressionContextScope() /Factory/;
+    QgsExpressionContextScope *defaultExpressionContextScope() const /Factory/;
 %Docstring
 Creates a new scope which contains default variables and functions relating to the map canvas.
 
@@ -705,6 +706,9 @@ Creates a new scope which contains default variables and functions relating to t
 .. versionadded:: 3.4
 %End
 
+    virtual QgsExpressionContext createExpressionContext() const;
+
+
     void setSegmentationTolerance( double tolerance );
 %Docstring
 Sets the segmentation tolerance applied when rendering curved geometries
diff --git a/src/gui/qgsmapcanvas.cpp b/src/gui/qgsmapcanvas.cpp
index 3f5c4ad446a1..2c35cf631dd7 100644
--- a/src/gui/qgsmapcanvas.cpp
+++ b/src/gui/qgsmapcanvas.cpp
@@ -514,14 +514,30 @@ QgsMapLayer *QgsMapCanvas::currentLayer()
   return mCurrentLayer;
 }
 
-QgsExpressionContextScope *QgsMapCanvas::defaultExpressionContextScope()
+QgsExpressionContextScope *QgsMapCanvas::defaultExpressionContextScope() const
 {
   QgsExpressionContextScope *s = new QgsExpressionContextScope( QObject::tr( "Map Canvas" ) );
   s->setVariable( QStringLiteral( "canvas_cursor_point" ), QgsGeometry::fromPointXY( cursorPoint() ), true );
-
   return s;
 }
 
+QgsExpressionContext QgsMapCanvas::createExpressionContext() const
+{
+  //build the expression context
+  QgsExpressionContext expressionContext;
+  expressionContext << QgsExpressionContextUtils::globalScope()
+                    << QgsExpressionContextUtils::projectScope( QgsProject::instance() )
+                    << QgsExpressionContextUtils::atlasScope( nullptr )
+                    << QgsExpressionContextUtils::mapSettingsScope( mSettings );
+  if ( QgsExpressionContextScopeGenerator *generator = dynamic_cast< QgsExpressionContextScopeGenerator * >( mController ) )
+  {
+    expressionContext << generator->createExpressionContextScope();
+  }
+  expressionContext << defaultExpressionContextScope()
+                    << new QgsExpressionContextScope( mExpressionContextScope );
+  return expressionContext;
+}
+
 void QgsMapCanvas::refresh()
 {
   if ( !mSettings.hasValidSettings() )
@@ -559,20 +575,7 @@ void QgsMapCanvas::refreshMap()
   stopRendering(); // if any...
   stopPreviewJobs();
 
-  //build the expression context
-  QgsExpressionContext expressionContext;
-  expressionContext << QgsExpressionContextUtils::globalScope()
-                    << QgsExpressionContextUtils::projectScope( QgsProject::instance() )
-                    << QgsExpressionContextUtils::atlasScope( nullptr )
-                    << QgsExpressionContextUtils::mapSettingsScope( mSettings );
-  if ( QgsExpressionContextScopeGenerator *generator = dynamic_cast< QgsExpressionContextScopeGenerator * >( mController ) )
-  {
-    expressionContext << generator->createExpressionContextScope();
-  }
-  expressionContext << defaultExpressionContextScope()
-                    << new QgsExpressionContextScope( mExpressionContextScope );
-
-  mSettings.setExpressionContext( expressionContext );
+  mSettings.setExpressionContext( createExpressionContext() );
   mSettings.setPathResolver( QgsProject::instance()->pathResolver() );
 
   if ( !mTheme.isEmpty() )
diff --git a/src/gui/qgsmapcanvas.h b/src/gui/qgsmapcanvas.h
index c613d8dd32f4..6bb56a8b8cb2 100644
--- a/src/gui/qgsmapcanvas.h
+++ b/src/gui/qgsmapcanvas.h
@@ -81,7 +81,7 @@ class QgsMapMouseEvent;
  * \brief Map canvas is a class for displaying all GIS data types on a canvas.
  */
 
-class GUI_EXPORT QgsMapCanvas : public QGraphicsView
+class GUI_EXPORT QgsMapCanvas : public QGraphicsView, public QgsExpressionContextGenerator
 {
 
 #ifdef SIP_RUN
@@ -658,7 +658,9 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
      * \see setExpressionContextScope()
      * \since QGIS 3.4
      */
-    QgsExpressionContextScope *defaultExpressionContextScope() SIP_FACTORY;
+    QgsExpressionContextScope *defaultExpressionContextScope() const SIP_FACTORY;
+
+    QgsExpressionContext createExpressionContext() const override;
 
     /**
      * Sets the segmentation tolerance applied when rendering curved geometries