Add subsetStringChanged signal

python/core/auto_generated/qgsvectorlayer.sip.in

@@ -2390,6 +2390,12 @@ Is emitted, whenever the fields available from this layer have been changed.
 This can be due to manually adding attributes or due to a join.
 %End
 
+    void subsetStringChanged();
+%Docstring
+Emitted when the layer's subset string has changed.
+
+.. versionadded:: 3.2
+%End
 
     void attributeValueChanged( QgsFeatureId fid, int idx, const QVariant &value );
 %Docstring

src/core/qgsvectorlayer.cpp

@@ -164,6 +164,8 @@ QgsVectorLayer::QgsVectorLayer( const QString &vectorLayerPath,
   connect( this, &QgsVectorLayer::selectionChanged, this, [ = ] { emit repaintRequested(); } );
   connect( QgsProject::instance()->relationManager(), &QgsRelationManager::relationsLoaded, this, &QgsVectorLayer::onRelationsLoaded );
 
+  connect( this, &QgsVectorLayer::subsetStringChanged, this, &QgsMapLayer::configChanged );
+
   // Default simplify drawing settings
   QgsSettings settings;
   mSimplifyMethod.setSimplifyHints( settings.flagValue( QStringLiteral( "qgis/simplifyDrawingHints" ), mSimplifyMethod.simplifyHints(), QgsSettings::NoSection ) );
@@ -897,7 +899,7 @@ bool QgsVectorLayer::setSubsetString( const QString &subset )
 
   if ( res )
   {
-    emit configChanged();
+    emit subsetStringChanged();
     emit repaintRequested();
   }
 

src/core/qgsvectorlayer.h

@@ -354,6 +354,7 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
 {
     Q_OBJECT
 
+    Q_PROPERTY( QString subsetString READ subsetString WRITE setSubsetString NOTIFY subsetStringChanged )
     Q_PROPERTY( QString displayExpression READ displayExpression WRITE setDisplayExpression NOTIFY displayExpressionChanged )
     Q_PROPERTY( QString mapTipTemplate READ mapTipTemplate WRITE setMapTipTemplate NOTIFY mapTipTemplateChanged )
     Q_PROPERTY( QgsEditFormConfig editFormConfig READ editFormConfig WRITE setEditFormConfig NOTIFY editFormConfigChanged )
@@ -2148,6 +2149,11 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      */
     void updatedFields();
 
+    /**
+     * Emitted when the layer's subset string has changed.
+     * \since QGIS 3.2
+     */
+    void subsetStringChanged();
 
     /**
      * Is emitted whenever an attribute value change is done in the edit buffer.

tests/src/python/test_qgsvectorlayer.py

@@ -1619,6 +1619,20 @@ def testUniqueStringsMatching(self):
         self.assertEqual(set(layer.uniqueStringsMatching(0, 'n')),
                          set(['orange', 'BanaNa', 'waterMelon', 'pineapple', 'coconut']))
 
+    def test_subsetString(self):
+        subset_string_changed = False
+
+        def onSubsetStringChanged():
+            nonlocal subset_string_changed
+            subset_string_changed = True
+
+        path = os.path.join(unitTestDataPath(), 'lines.shp')
+        layer = QgsVectorLayer(path, 'test', 'ogr')
+        layer.subsetStringChanged.connect(onSubsetStringChanged)
+        layer.setSubsetString("\"Name\" = 'Highway'")
+        self.assertTrue(subset_string_changed)
+        self.assertEqual(layer.featureCount(), 2)
+
     def testMinValue(self):
         """ test retrieving minimum values """
         layer = createLayerWithFivePoints()