[OGR provider] When editing a GeoJSON file, close and re-open the file at end of editing session (fixes #18596)

Author: rouault

src/providers/ogr/qgsogrprovider.cpp

@@ -4160,6 +4160,13 @@ bool QgsOgrProvider::leaveUpdateMode()
   }
   if ( !mDynamicWriteAccess )
   {
+    // The GeoJSON driver only properly flushes stuff in all situations by
+    // closing and re-opening. Starting with GDAL 2.3.1, it should be safe to
+    // use GDALDatasetFlush().
+    if ( mGDALDriverName == QLatin1String( "GeoJSON" ) )
+    {
+      reloadData();
+    }
     return true;
   }
   if ( mUpdateModeStackDepth == 0 )

tests/src/python/test_provider_ogr.py

@@ -318,6 +318,28 @@ def testSetupProxy(self):
         self.assertEqual(gdal.GetConfigOption("GDAL_HTTP_PROXY"), "myproxyhostname.com")
         self.assertEqual(gdal.GetConfigOption("GDAL_HTTP_PROXYUSERPWD"), "username")
 
+    def testEditGeoJson(self):
+        """ Test bugfix of https://issues.qgis.org/issues/18596 """
+
+        datasource = os.path.join(self.basetestpath, 'testEditGeoJson.json')
+        with open(datasource, 'wt') as f:
+            f.write("""{
+"type": "FeatureCollection",
+"features": [
+{ "type": "Feature", "properties": { "x": 1, "y": 2, "z": 3, "w": 4 }, "geometry": { "type": "Point", "coordinates": [ 0, 0 ] } } ] }""")
+
+        vl = QgsVectorLayer(datasource, 'test', 'ogr')
+        self.assertTrue(vl.isValid())
+        self.assertTrue(vl.startEditing())
+        self.assertTrue(vl.deleteAttribute(1))
+        self.assertTrue(vl.commitChanges())
+
+        f = QgsFeature()
+        self.assertTrue(vl.getFeatures(QgsFeatureRequest()).nextFeature(f))
+        self.assertEqual(f['x'], 1)
+        self.assertEqual(f['z'], 3)
+        self.assertEqual(f['w'], 4)
+
 
 if __name__ == '__main__':
     unittest.main()