with edit(layer) raises an error if the commit fails

python/core/__init__.py

@@ -135,6 +135,13 @@ try:
 except ImportError:
     pass
 
+class QgsEditError(Exception):
+    def __init__(self, value):
+        self.value = value
+
+    def __str__(self):
+        return repr(self.value)
+
 # Define a `with edit(layer)` statement
 
 class edit:
@@ -147,7 +154,8 @@ class edit:
 
     def __exit__(self, ex_type, ex_value, traceback):
         if ex_type is None:
-            assert self.layer.commitChanges()
+            if not self.layer.commitChanges():
+                raise QgsEditError(self.layer.commitErrors())
             return True
         else:
             self.layer.rollBack()

tests/src/python/test_syntactic_sugar.py

@@ -21,7 +21,8 @@ from utilities import (unittest,
 from qgis.core import (edit,
                        QgsFeature,
                        QgsGeometry,
-                       QgsVectorLayer
+                       QgsVectorLayer,
+                       QgsEditError
                       )
 
 getQgisTestApp()
@@ -72,5 +73,10 @@ class TestSyntacticSugar(TestCase):
 
         assert ml.dataProvider().getFeatures().next()['value']==10
 
+        # Check that we get a QgsEditError exception when the commit fails
+        with self.assertRaises(QgsEditError):
+          with edit(ml) as l:
+              l.rollBack()
+
 if __name__ == "__main__":
         unittest.main()