Ensure created memory layers have unique source

Sometimes the layer source is used for "looser" comparison then
layer ID

Author: nyalldawson

src/core/providers/memory/qgsmemoryproviderutils.cpp

@@ -65,6 +65,8 @@ QgsVectorLayer *QgsMemoryProviderUtils::createMemoryLayer( const QString &name,
   {
     parts << QStringLiteral( "field=%1:%2" ).arg( field.name(), memoryLayerFieldType( field.type() ) );
   }
+  // required so that source differs between memory layers
+  parts << QStringLiteral( "uid=%1" ).arg( QUuid::createUuid().toString() );
 
   QString uri = geomType + '?' + parts.join( '&' );
 

tests/src/python/test_provider_memory.py

@@ -349,6 +349,10 @@ def testCreateMemoryLayer(self):
         self.assertEqual(layer.name(), 'my name')
         self.assertTrue(layer.fields().isEmpty())
 
+        # similar layers should have unique sources
+        layer2 = QgsMemoryProviderUtils.createMemoryLayer('my name', QgsFields())
+        self.assertNotEqual(layer.source(), layer2.source())
+
         # geometry type
         layer = QgsMemoryProviderUtils.createMemoryLayer('my name', QgsFields(), QgsWkbTypes.Point)
         self.assertTrue(layer.isValid())