[composer] Fix setting legend content by map not resizing legend

When a legend was set to filter content by map, it wasn't
consistently being resized to fit the legend contents. This caused
issues for atlas exports where legends could grow but never
shrink.

Fix #14707

On behalf of Faunalia, sponsored by ENEL

(cherry-picked from 4f31ab6)

src/core/composer/qgscomposerlegend.cpp

@@ -43,6 +43,7 @@ QgsComposerLegend::QgsComposerLegend( QgsComposition* composition )
     , mFilterAskedForUpdate( false )
     , mInAtlas( false )
     , mInitialMapScaleCalculated( false )
+    , mForceResize( false )
 {
   mLegendModel2 = new QgsLegendModelV2( QgsProject::instance()->layerTreeRoot() );
 
@@ -66,6 +67,8 @@ QgsComposerLegend::QgsComposerLegend()
     , mFilterOutAtlas( false )
     , mFilterAskedForUpdate( false )
     , mInAtlas( false )
+    , mInitialMapScaleCalculated( false )
+    , mForceResize( false )
 {
 
 }
@@ -117,11 +120,18 @@ void QgsComposerLegend::paint( QPainter* painter, const QStyleOptionGraphicsItem
   mInitialMapScaleCalculated = true;
 
   QgsLegendRenderer legendRenderer( mLegendModel2, mSettings );
-  legendRenderer.setLegendSize( rect().size() );
+  legendRenderer.setLegendSize( mForceResize ? QSize() : rect().size() );
 
   //adjust box if width or height is too small
   QSizeF size = legendRenderer.minimumSize();
-  if ( size.height() > rect().height() || size.width() > rect().width() )
+  if ( mForceResize )
+  {
+    mForceResize = false;
+    //set new rect, respecting position mode and data defined size/position
+    QRectF targetRect = QRectF( pos().x(), pos().y(), size.width(), size.height() );
+    setSceneRect( evalItemRect( targetRect, true ) );
+  }
+  else if ( size.height() > rect().height() || size.width() > rect().width() )
   {
     //need to resize box
     QRectF targetRect = QRectF( pos().x(), pos().y(), rect().width(), rect().height() );
@@ -674,6 +684,8 @@ void QgsComposerLegend::doUpdateFilterByMap()
   }
   else
     mLegendModel2->setLegendFilterByMap( nullptr );
+
+  mForceResize = true;
 }
 
 void QgsComposerLegend::setLegendFilterOutAtlas( bool doFilter )

src/core/composer/qgscomposerlegend.h

@@ -296,6 +296,9 @@ class CORE_EXPORT QgsComposerLegend : public QgsComposerItem
 
     //! Will be false until the associated map scale and DPI have been calculated
     bool mInitialMapScaleCalculated;
+
+    //! Will be true if the legend size should be totally reset at next paint
+    bool mForceResize;
 };
 
 #endif

tests/src/python/test_qgscomposerlegend.py

@@ -22,7 +22,8 @@
                        QgsVectorLayer,
                        QgsMapLayerRegistry,
                        QgsMarkerSymbolV2,
-                       QgsSingleSymbolRendererV2
+                       QgsSingleSymbolRendererV2,
+                       QgsRectangle
                        )
 from qgis.testing import (start_app,
                           unittest
@@ -37,30 +38,27 @@
 
 class TestQgsComposerLegend(unittest.TestCase):
 
-    def __init__(self, methodName):
-        """Run once on class initialization."""
-        unittest.TestCase.__init__(self, methodName)
-        point_path = os.path.join(TEST_DATA_DIR, 'points.shp')
-        self.point_layer = QgsVectorLayer(point_path, 'points', 'ogr')
-        QgsMapLayerRegistry.instance().addMapLayers([self.point_layer])
-
     def testInitialSizeSymbolMapUnits(self):
         """Test initial size of legend with a symbol size in map units"""
 
+        point_path = os.path.join(TEST_DATA_DIR, 'points.shp')
+        point_layer = QgsVectorLayer(point_path, 'points', 'ogr')
+        QgsMapLayerRegistry.instance().addMapLayers([point_layer])
+
         marker_symbol = QgsMarkerSymbolV2.createSimple({'color': '#ff0000', 'outline_style': 'no', 'size': '5', 'size_unit': 'MapUnit'})
 
-        self.point_layer.setRendererV2(QgsSingleSymbolRendererV2(marker_symbol))
+        point_layer.setRendererV2(QgsSingleSymbolRendererV2(marker_symbol))
 
         s = QgsMapSettings()
-        s.setLayers([self.point_layer.id()])
+        s.setLayers([point_layer.id()])
         s.setCrsTransformEnabled(False)
         composition = QgsComposition(s)
         composition.setPaperSize(297, 210)
 
         composer_map = QgsComposerMap(composition, 20, 20, 80, 80)
         composer_map.setFrameEnabled(True)
         composition.addComposerMap(composer_map)
-        composer_map.setNewExtent(self.point_layer.extent())
+        composer_map.setNewExtent(point_layer.extent())
 
         legend = QgsComposerLegend(composition)
         legend.setSceneRect(QRectF(120, 20, 80, 80))
@@ -77,6 +75,46 @@ def testInitialSizeSymbolMapUnits(self):
         result, message = checker.testComposition()
         self.assertTrue(result, message)
 
+        QgsMapLayerRegistry.instance().removeMapLayers([point_layer])
+
+    def testResizeWithMapContent(self):
+        """Test test legend resizes to match map content"""
+
+        point_path = os.path.join(TEST_DATA_DIR, 'points.shp')
+        point_layer = QgsVectorLayer(point_path, 'points', 'ogr')
+        QgsMapLayerRegistry.instance().addMapLayers([point_layer])
+
+        s = QgsMapSettings()
+        s.setLayers([point_layer.id()])
+        s.setCrsTransformEnabled(False)
+        composition = QgsComposition(s)
+        composition.setPaperSize(297, 210)
+
+        composer_map = QgsComposerMap(composition, 20, 20, 80, 80)
+        composer_map.setFrameEnabled(True)
+        composition.addComposerMap(composer_map)
+        composer_map.setNewExtent(point_layer.extent())
+
+        legend = QgsComposerLegend(composition)
+        legend.setSceneRect(QRectF(120, 20, 80, 80))
+        legend.setFrameEnabled(True)
+        legend.setFrameOutlineWidth(2)
+        legend.setBackgroundColor(QColor(200, 200, 200))
+        legend.setTitle('')
+        legend.setLegendFilterByMapEnabled(True)
+        composition.addComposerLegend(legend)
+        legend.setComposerMap(composer_map)
+
+        composer_map.setNewExtent(QgsRectangle(-102.51, 41.16, -102.36, 41.30))
+
+        checker = QgsCompositionChecker(
+            'composer_legend_size_content', composition)
+        checker.setControlPathPrefix("composer_legend")
+        result, message = checker.testComposition()
+        self.assertTrue(result, message)
+
+        QgsMapLayerRegistry.instance().removeMapLayers([point_layer])
+
 
 if __name__ == '__main__':
     unittest.main()