Fix Node.treerepr if mapping raises an exception on __getitem__.

Author: rnixx

src/node/behaviors/node.py

@@ -133,12 +133,19 @@ def collect_schema_members(cls):
                 for name in schema_members
             ], key=lambda x: x[0])
         if IMappingNode.providedBy(self):
-            items = (
-                self.items()
+            items = list()
+            for key in self:
+                try:
+                    value = self[key]
+                except Exception as e:
+                    value = repr(e)
+                items.append((key, value))
+            sorted_items = (
+                items
                 if IOrdered.providedBy(self)
-                else sorted(self.items(), key=lambda x: safe_decode(x[0]))
+                else sorted(items, key=lambda x: safe_decode(x[0]))
             )
-            for item in items:
+            for item in sorted_items:
                 if item[0] not in schema_members:
                     children.append(item)
         elif ISequenceNode.providedBy(self):

src/node/tests/test_node.py

@@ -1,4 +1,5 @@
 from node.behaviors import DefaultInit
+from node.behaviors import MappingNode
 from node.behaviors import Node
 from node.behaviors import NodeInit
 from node.interfaces import IDefaultInit
@@ -31,6 +32,13 @@ class NodeObject(object):
     pass
 
 
+@plumbing(DefaultInit, Node, MappingNode)
+class BrokenMapping(object):
+
+    def __iter__(self):
+        yield 'child'
+
+
 class NoInterface(Interface):
     pass
 
@@ -98,3 +106,10 @@ def test_Node(self):
             node.noderepr,
             "<class 'node.tests.test_node.NodeObject'>: node"
         )
+
+        # treerepr
+        broken = BrokenMapping(name='broken')
+        self.checkOutput("""
+        <class 'node.tests.test_node.BrokenMapping'>: broken
+        __child: 'NotImplementedError()'
+        """, broken.treerepr(prefix='_'))