qgsvectorlayer: Properly invalidate extent cache on feature addition

When a new feature is added to a `QgsVectorLayer`
`QgsVectorLayer::addFeature` is called. This function makes mostly 2
things in case of a successful operation:
1. it calls `QgsVectorLayerEditBuffer::addFeature` which itself will
   emit the `QgsVectorLayerEditBuffer::featureAdded` signal. Finally,
   `QgsVectorLayer` listend to this signal to directly emit the
   `QgsVectorLayer::featureAdded` signal
2. Call `QgsVectorLayer::updateExtents()` to invalidate the cache of
   the extent

In practice, this means that the `QgsVectorLayer::featureAdded` signal
may be emitted before the cache of the extent is invalidated. This can
cause some issues.

For example, in the elevation profile tool,
`QgsElevationProfileCanvas` listens to the
`QgsVectorLayer::featureAdded` signal in order to regenerate the
profile of a vector layer when a feature is added. This causes the
creation of a new `QgsVectorLayerProfileGenerator` which needs to copy
the extent of the vector layer. However,
`QgsVectorLayer::updateExtents()` has not been called yet. Thus, it
will use an outdated version of the extent.

This issue is solved by calling `updateExtents()` before emitting the
`featureAdded` signal.

src/core/vector/qgsvectorlayer.cpp

@@ -1366,12 +1366,9 @@ bool QgsVectorLayer::addFeature( QgsFeature &feature, Flags )
 
   bool success = mEditBuffer->addFeature( feature );
 
-  if ( success )
+  if ( success && mJoinBuffer->containsJoins() )
   {
-    updateExtents();
-
-    if ( mJoinBuffer->containsJoins() )
-      success = mJoinBuffer->addFeature( feature );
+    success = mJoinBuffer->addFeature( feature );
   }
 
   return success;
@@ -5080,7 +5077,7 @@ void QgsVectorLayer::createEditBuffer()
   connect( mEditBuffer, &QgsVectorLayerEditBuffer::layerModified, this, &QgsVectorLayer::invalidateSymbolCountedFlag );
   connect( mEditBuffer, &QgsVectorLayerEditBuffer::layerModified, this, &QgsVectorLayer::layerModified ); // TODO[MD]: necessary?
   //connect( mEditBuffer, SIGNAL( layerModified() ), this, SLOT( triggerRepaint() ) ); // TODO[MD]: works well?
-  connect( mEditBuffer, &QgsVectorLayerEditBuffer::featureAdded, this, &QgsVectorLayer::featureAdded );
+  connect( mEditBuffer, &QgsVectorLayerEditBuffer::featureAdded, this, &QgsVectorLayer::onFeatureAdded );
   connect( mEditBuffer, &QgsVectorLayerEditBuffer::featureDeleted, this, &QgsVectorLayer::onFeatureDeleted );
   connect( mEditBuffer, &QgsVectorLayerEditBuffer::geometryChanged, this, &QgsVectorLayer::geometryChanged );
   connect( mEditBuffer, &QgsVectorLayerEditBuffer::attributeValueChanged, this, &QgsVectorLayer::attributeValueChanged );
@@ -5966,6 +5963,15 @@ void QgsVectorLayer::onJoinedFieldsChanged()
   updateFields();
 }
 
+void QgsVectorLayer::onFeatureAdded( QgsFeatureId fid )
+{
+  QGIS_PROTECT_QOBJECT_THREAD_ACCESS
+
+  updateExtents();
+
+  emit featureAdded( fid );
+}
+
 void QgsVectorLayer::onFeatureDeleted( QgsFeatureId fid )
 {
   QGIS_PROTECT_QOBJECT_THREAD_ACCESS

src/core/vector/qgsvectorlayer.h

@@ -2797,6 +2797,7 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
     void onFeatureCounterCompleted();
     void onFeatureCounterTerminated();
     void onJoinedFieldsChanged();
+    void onFeatureAdded( QgsFeatureId fid );
     void onFeatureDeleted( QgsFeatureId fid );
     void onRelationsLoaded();
     void onSymbolsCounted();

tests/src/core/testqgsvectorlayer.cpp

@@ -76,6 +76,7 @@ class TestQgsVectorLayer : public QgsTest
     void testCopyPasteFieldConfiguration_data();
     void testFieldExpression();
     void testFieldAggregateExpression();
+    void testAddFeatureExtentUpdated();
 };
 
 void TestQgsVectorLayer::initTestCase()
@@ -495,6 +496,33 @@ void TestQgsVectorLayer::testFieldAggregateExpression()
   QVERIFY( qgsDoubleNear( feature2.attribute( vfIndex ).toDouble(), 359065580.0, 1 ) );
 }
 
+void TestQgsVectorLayer::testAddFeatureExtentUpdated()
+{
+  QgsVectorLayer *layerLine = new QgsVectorLayer( QStringLiteral( "LineString?crs=EPSG:27700" ), QStringLiteral( "layer line" ), QStringLiteral( "memory" ) );
+  QVERIFY( layerLine->isValid() );
+  QCOMPARE( layerLine->featureCount(), static_cast<long>( 0 ) );
+  QCOMPARE( layerLine->extent(), QgsRectangle() );
+
+  const QSignalSpy spyAdded( layerLine, &QgsVectorLayer::featureAdded );
+
+  QgsFeature lineF1;
+  lineF1.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "LineString (2 1, 1 1, 1 5, 7 12)" ) ) );
+
+  connect( layerLine, &QgsVectorLayer::featureAdded, this, [&layerLine, &lineF1]( const QgsFeatureId &fid ) {
+    QCOMPARE( fid, lineF1.id() );
+    QCOMPARE( layerLine->extent(), QgsRectangle( 1, 1, 7, 12 ) );
+    QCOMPARE( layerLine->extent3D(), QgsBox3D( 1, 1, std::numeric_limits<double>::quiet_NaN(), 7, 12, std::numeric_limits<double>::quiet_NaN() ) );
+  } );
+
+  layerLine->startEditing();
+  layerLine->addFeature( lineF1 );
+  QCOMPARE( spyAdded.count(), 1 );
+  QCOMPARE( layerLine->featureCount(), static_cast<long>( 1 ) );
+  QCOMPARE( spyAdded.at( 0 ).at( 0 ), QVariant( lineF1.id() ) );
+
+  delete layerLine;
+}
+
 
 QGSTEST_MAIN( TestQgsVectorLayer )
 #include "testqgsvectorlayer.moc"