[pal] Don't treat joined features as obstacles for each other

Eg, if the "merge connected features" option for a layer is checked
then label candidates generated for the merged line should not
be marked as in conflict with any part of the merged line.
Previously they would be marked in conflict with all but one part
of the merged line, resulting in false penalties being applied
to these candidates and non-ideal final label placements.

src/core/pal/feature.cpp

@@ -170,7 +170,18 @@ namespace pal
     if ( !part )
       return false;
 
-    return mLF->id() == part->featureId() && mLF->layer()->name() == part->layer()->name();
+    if ( mLF->layer()->name() != part->layer()->name() )
+      return false;
+
+    if ( mLF->id() == part->featureId() )
+      return true;
+
+    // any part of joined features are also treated as having the same label feature
+    int connectedFeatureId = mLF->layer()->connectedFeatureId( mLF->id() );
+    if ( connectedFeatureId >= 0 && connectedFeatureId == mLF->layer()->connectedFeatureId( part->featureId() ) )
+      return true;
+
+    return false;
   }
 
   LabelPosition::Quadrant FeaturePart::quadrantFromOffset() const

src/core/pal/layer.cpp

@@ -357,11 +357,14 @@ namespace pal
   void Layer::joinConnectedFeatures()
   {
     // go through all label texts
+    int connectedFeaturesId = 0;
     Q_FOREACH ( const QString& labelText, mConnectedTexts )
     {
       if ( !mConnectedHashtable.contains( labelText ) )
         continue; // shouldn't happen
 
+      connectedFeaturesId++;
+
       QLinkedList<FeaturePart*>* parts = mConnectedHashtable.value( labelText );
 
       // go one-by-one part, try to merge
@@ -381,11 +384,13 @@ namespace pal
           mFeatureIndex->Remove( bmin, bmax, partCheck );
           mFeatureParts.removeOne( partCheck );
 
+          mConnectedFeaturesIds.insert( partCheck->featureId(), connectedFeaturesId );
           otherPart->getBoundingBox( bmin, bmax );
 
           // merge points from partCheck to p->item
           if ( otherPart->mergeWithFeaturePart( partCheck ) )
           {
+            mConnectedFeaturesIds.insert( otherPart->featureId(), connectedFeaturesId );
             // reinsert p->item to r-tree (probably not needed)
             mFeatureIndex->Remove( bmin, bmax, otherPart );
             otherPart->getBoundingBox( bmin, bmax );
@@ -409,6 +414,11 @@ namespace pal
     mConnectedTexts.clear();
   }
 
+  int Layer::connectedFeatureId( QgsFeatureId featureId ) const
+  {
+    return mConnectedFeaturesIds.value( featureId, -1 );
+  }
+
   void Layer::chopFeaturesAtRepeatDistance()
   {
     GEOSContextHandle_t geosctxt = geosContext();

src/core/pal/layer.h

@@ -239,6 +239,12 @@ namespace pal
       /** Join connected features with the same label text */
       void joinConnectedFeatures();
 
+      /** Returns the connected feature ID for a label feature ID, which is unique for all features
+       * which have been joined as a result of joinConnectedFeatures()
+       * @returns connected feature ID, or -1 if feature was not joined
+       */
+      int connectedFeatureId( QgsFeatureId featureId ) const;
+
       /** Chop layer features at the repeat distance **/
       void chopFeaturesAtRepeatDistance();
 
@@ -281,6 +287,7 @@ namespace pal
 
       QHash< QString, QLinkedList<FeaturePart*>* > mConnectedHashtable;
       QStringList mConnectedTexts;
+      QHash< QgsFeatureId, int > mConnectedFeaturesIds;
 
       QMutex mMutex;