Fix legend count is 0 if graduated/categorized expression uses geometry

Likely fixes many other bugs too with graduated/categorized renderers

Fixes #15544

Author: nyalldawson

python/core/auto_generated/symbology/qgscategorizedsymbolrenderer.sip.in

@@ -93,6 +93,8 @@ class QgsCategorizedSymbolRenderer : QgsFeatureRenderer
 
     virtual QSet<QString> usedAttributes( const QgsRenderContext &context ) const;
 
+    virtual bool filterNeedsGeometry() const;
+
     virtual QString dump() const;
 
     virtual QgsCategorizedSymbolRenderer *clone() const /Factory/;

python/core/auto_generated/symbology/qgsgraduatedsymbolrenderer.sip.in

@@ -130,6 +130,8 @@ class QgsGraduatedSymbolRenderer : QgsFeatureRenderer
 
     virtual QSet<QString> usedAttributes( const QgsRenderContext &context ) const;
 
+    virtual bool filterNeedsGeometry() const;
+
     virtual QString dump() const;
 
     virtual QgsGraduatedSymbolRenderer *clone() const /Factory/;

src/core/symbology/qgscategorizedsymbolrenderer.cpp

@@ -452,6 +452,19 @@ QSet<QString> QgsCategorizedSymbolRenderer::usedAttributes( const QgsRenderConte
   return attributes;
 }
 
+bool QgsCategorizedSymbolRenderer::filterNeedsGeometry() const
+{
+  QgsExpression testExpr( mAttrName );
+  if ( !testExpr.hasParserError() )
+  {
+    QgsExpressionContext context;
+    context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( nullptr ) ); // unfortunately no layer access available!
+    testExpr.prepare( &context );
+    return testExpr.needsGeometry();
+  }
+  return false;
+}
+
 QString QgsCategorizedSymbolRenderer::dump() const
 {
   QString s = QStringLiteral( "CATEGORIZED: idx %1\n" ).arg( mAttrName );

src/core/symbology/qgscategorizedsymbolrenderer.h

@@ -102,6 +102,7 @@ class CORE_EXPORT QgsCategorizedSymbolRenderer : public QgsFeatureRenderer
     void startRender( QgsRenderContext &context, const QgsFields &fields ) override;
     void stopRender( QgsRenderContext &context ) override;
     QSet<QString> usedAttributes( const QgsRenderContext &context ) const override;
+    bool filterNeedsGeometry() const override;
     QString dump() const override;
     QgsCategorizedSymbolRenderer *clone() const override SIP_FACTORY;
     void toSld( QDomDocument &doc, QDomElement &element, const QgsStringMap &props = QgsStringMap() ) const override;

src/core/symbology/qgsgraduatedsymbolrenderer.cpp

@@ -425,6 +425,19 @@ QSet<QString> QgsGraduatedSymbolRenderer::usedAttributes( const QgsRenderContext
   return attributes;
 }
 
+bool QgsGraduatedSymbolRenderer::filterNeedsGeometry() const
+{
+  QgsExpression testExpr( mAttrName );
+  if ( !testExpr.hasParserError() )
+  {
+    QgsExpressionContext context;
+    context.appendScopes( QgsExpressionContextUtils::globalProjectLayerScopes( nullptr ) ); // unfortunately no layer access available!
+    testExpr.prepare( &context );
+    return testExpr.needsGeometry();
+  }
+  return false;
+}
+
 bool QgsGraduatedSymbolRenderer::updateRangeSymbol( int rangeIndex, QgsSymbol *symbol )
 {
   if ( rangeIndex < 0 || rangeIndex >= mRanges.size() )

src/core/symbology/qgsgraduatedsymbolrenderer.h

@@ -152,6 +152,7 @@ class CORE_EXPORT QgsGraduatedSymbolRenderer : public QgsFeatureRenderer
     void startRender( QgsRenderContext &context, const QgsFields &fields ) override;
     void stopRender( QgsRenderContext &context ) override;
     QSet<QString> usedAttributes( const QgsRenderContext &context ) const override;
+    bool filterNeedsGeometry() const override;
     QString dump() const override;
     QgsGraduatedSymbolRenderer *clone() const override SIP_FACTORY;
     void toSld( QDomDocument &doc, QDomElement &element, const QgsStringMap &props = QgsStringMap() ) const override;

tests/src/python/test_qgscategorizedsymbolrenderer.py

@@ -458,6 +458,31 @@ def testMatchToSymbols(self):
         self.assertEqual(symbol.color().name(), '#0aff0a')
         renderer.stopRender(context)
 
+    def testUsedAttributes(self):
+        renderer = QgsCategorizedSymbolRenderer()
+        ctx = QgsRenderContext()
+
+        # attribute can contain either attribute name or an expression.
+        # Sometimes it is not possible to distinguish between those two,
+        # e.g. "a - b" can be both a valid attribute name or expression.
+        # Since we do not have access to fields here, the method should return both options.
+        renderer.setClassAttribute("value")
+        self.assertEqual(renderer.usedAttributes(ctx), {"value"})
+        renderer.setClassAttribute("value - 1")
+        self.assertEqual(renderer.usedAttributes(ctx), {"value", "value - 1"})
+        renderer.setClassAttribute("valuea - valueb")
+        self.assertEqual(renderer.usedAttributes(ctx), {"valuea", "valuea - valueb", "valueb"})
+
+    def testFilterNeedsGeometry(self):
+        renderer = QgsCategorizedSymbolRenderer()
+
+        renderer.setClassAttribute("value")
+        self.assertFalse(renderer.filterNeedsGeometry())
+        renderer.setClassAttribute("$area")
+        self.assertTrue(renderer.filterNeedsGeometry())
+        renderer.setClassAttribute("value - $area")
+        self.assertTrue(renderer.filterNeedsGeometry())
+
 
 if __name__ == "__main__":
     unittest.main()

tests/src/python/test_qgsgraduatedsymbolrenderer.py

@@ -450,11 +450,30 @@ def testQgsGraduatedSymbolRenderer_3(self):
             '(0.5000-1.0000,1.0000-1.1000,1.1000-1.2000,1.2000-5.0000,)',
             'Quantile classification not correct')
 
-        # Tests still needed
+    def testUsedAttributes(self):
+        renderer = QgsGraduatedSymbolRenderer()
+        ctx = QgsRenderContext()
+
+        # attribute can contain either attribute name or an expression.
+        # Sometimes it is not possible to distinguish between those two,
+        # e.g. "a - b" can be both a valid attribute name or expression.
+        # Since we do not have access to fields here, the method should return both options.
+        renderer.setClassAttribute("value")
+        self.assertEqual(renderer.usedAttributes(ctx), {"value"})
+        renderer.setClassAttribute("value - 1")
+        self.assertEqual(renderer.usedAttributes(ctx), {"value", "value - 1"})
+        renderer.setClassAttribute("valuea - valueb")
+        self.assertEqual(renderer.usedAttributes(ctx), {"valuea", "valuea - valueb", "valueb"})
 
-        # Other calculation method tests
-        # createRenderer function
-        # symbolForFeature correctly selects range
+    def testFilterNeedsGeometry(self):
+        renderer = QgsGraduatedSymbolRenderer()
+
+        renderer.setClassAttribute("value")
+        self.assertFalse(renderer.filterNeedsGeometry())
+        renderer.setClassAttribute("$area")
+        self.assertTrue(renderer.filterNeedsGeometry())
+        renderer.setClassAttribute("value - $area")
+        self.assertTrue(renderer.filterNeedsGeometry())
 
 
 if __name__ == "__main__":