Address review, add test case

src/core/pal/layer.cpp

@@ -342,7 +342,12 @@ void Layer::joinConnectedFeatures()
   // Expunge feature parts that are smaller than the minimum size required
   mFeatureParts.erase( std::remove_if( mFeatureParts.begin(), mFeatureParts.end(), []( FeaturePart * part )
   {
-    return part->feature()->minimumSize() != 0.0 && part->length() < part->feature()->minimumSize();
+    if ( part->feature()->minimumSize() != 0.0 && part->length() < part->feature()->minimumSize() )
+    {
+      delete part;
+      return true;
+    }
+    return false;
   } ), mFeatureParts.end() );
 }
 

tests/src/core/testqgslabelingengine.cpp

@@ -62,6 +62,7 @@ class TestQgsLabelingEngine : public QObject
     void testAdjacentParts();
     void testTouchingParts();
     void testMergingLinesWithForks();
+    void testMergingLinesWithMinimumSize();
     void testCurvedLabelsWithTinySegments();
     void testCurvedLabelCorrectLinePlacement();
     void testCurvedLabelNegativeDistance();
@@ -1198,6 +1199,73 @@ void TestQgsLabelingEngine::testMergingLinesWithForks()
   QVERIFY( imageCheck( QStringLiteral( "label_multipart_touching_branches" ), img, 20 ) );
 }
 
+void TestQgsLabelingEngine::testMergingLinesWithMinimumSize()
+{
+  // test that the "merge connected features" setting works well with
+  // a non-zero minimum feature size value
+  QgsPalLayerSettings settings;
+  setDefaultLabelParams( settings );
+
+  QgsTextFormat format = settings.format();
+  format.setSize( 20 );
+  format.setColor( QColor( 0, 0, 0 ) );
+  settings.setFormat( format );
+
+  settings.fieldName = QStringLiteral( "'XX'" );
+  settings.isExpression = true;
+  settings.placement = QgsPalLayerSettings::Curved;
+  settings.labelPerPart = false;
+  settings.lineSettings().setMergeLines( true );
+  settings.thinningSettings().setMinimumFeatureSize( 90.0 );
+
+  // if treated individually, none of these parts are long enough for the label to fit -- but the label should be rendered if the mergeLines setting is true
+  std::unique_ptr< QgsVectorLayer> vl2( new QgsVectorLayer( QStringLiteral( "LineString?crs=epsg:3946&field=id:integer" ), QStringLiteral( "vl" ), QStringLiteral( "memory" ) ) );
+  vl2->setRenderer( new QgsNullSymbolRenderer() );
+
+  QgsFeature f;
+  f.setAttributes( QgsAttributes() << 1 );
+  f.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "LineString (190000 5000010, 190100 5000000)" ) ) );
+  QVERIFY( vl2->dataProvider()->addFeature( f ) );
+  // side branch
+  f.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "LineString (190100 5000000, 190100 5000010)" ) ) );
+  QVERIFY( vl2->dataProvider()->addFeature( f ) );
+  // side branch
+  f.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "LineString (190100 5000000, 190100 4999995)" ) ) );
+  QVERIFY( vl2->dataProvider()->addFeature( f ) );
+  // main road continues, note that we deliberately split this up into non-consecutive sections, just for extra checks!
+  f.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "LineString (190120 5000000, 190200 5000000)" ) ) );
+  QVERIFY( vl2->dataProvider()->addFeature( f ) );
+  f.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "LineString (190120 5000000, 190100 5000000)" ) ) );
+  QVERIFY( vl2->dataProvider()->addFeature( f ) );
+
+  vl2->setLabeling( new QgsVectorLayerSimpleLabeling( settings ) );  // TODO: this should not be necessary!
+  vl2->setLabelsEnabled( true );
+
+  // make a fake render context
+  QSize size( 640, 480 );
+  QgsMapSettings mapSettings;
+  mapSettings.setLabelingEngineSettings( createLabelEngineSettings() );
+  mapSettings.setDestinationCrs( vl2->crs() );
+
+  mapSettings.setOutputSize( size );
+  mapSettings.setExtent( vl2->extent() );
+  mapSettings.setLayers( QList<QgsMapLayer *>() << vl2.get() );
+  mapSettings.setOutputDpi( 96 );
+
+  QgsLabelingEngineSettings engineSettings = mapSettings.labelingEngineSettings();
+  engineSettings.setFlag( QgsLabelingEngineSettings::UsePartialCandidates, false );
+  engineSettings.setFlag( QgsLabelingEngineSettings::DrawLabelRectOnly, true );
+  //engineSettings.setFlag( QgsLabelingEngineSettings::DrawCandidates, true );
+  mapSettings.setLabelingEngineSettings( engineSettings );
+
+  QgsMapRendererSequentialJob job( mapSettings );
+  job.start();
+  job.waitForFinished();
+
+  QImage img = job.renderedImage();
+  QVERIFY( imageCheck( QStringLiteral( "label_merged_minimum_size" ), img, 20 ) );
+}
+
 void TestQgsLabelingEngine::testCurvedLabelsWithTinySegments()
 {
   // test drawing curved labels when input linestring has many small segments