Add absolute path and absolute schema path.

Closes #120

3 files changed, 154 insertions, 35 deletions

diff --git a/docs/errors.rst b/docs/errors.rst
index d49954f..1956c35 100644
--- a/docs/errors.rst
+++ b/docs/errors.rst
@@ -49,16 +49,40 @@ raised or returned, depending on which method or function is used.
         subschema from within the schema that was passed into the validator, or
         even an entirely different schema if a :validator:`$ref` was followed.
 
-    .. attribute:: schema_path
+    .. attribute:: relative_schema_path
 
         A :class:`collections.deque` containing the path to the failed
         validator within the schema.
 
+    .. attribute:: absolute_schema_path
+
+        A :class:`collections.deque` containing the path to the failed
+        validator within the schema, but always relative to the
+        *original* schema as opposed to any subschema (i.e. the one
+        originally passed into a validator, *not* :attr:`schema`\).
+
+    .. attribute:: schema_path
+
+        Same as :attr:`relative_schema_path`.
+
+    .. attribute:: relative_path
+
+        A :class:`collections.deque` containing the path to the
+        offending element within the instance. The deque can be empty if
+        the error happened at the root of the instance.
+
+    .. attribute:: absolute_path
+
+        A :class:`collections.deque` containing the path to the
+        offending element within the instance. The absolute path
+        is always relative to the *original* instance that was
+        validated (i.e. the one passed into a validation method, *not*
+        :attr:`instance`\). The deque can be empty if the error happened
+        at the root of the instance.
+
     .. attribute:: path
 
-        A :class:`collections.deque` containing the path to the offending
-        element within the instance. The deque can be empty if the error
-        happened at the root of the instance.
+        Same as :attr:`relative_path`.
 
     .. attribute:: instance
 
@@ -82,6 +106,11 @@ raised or returned, depending on which method or function is used.
         object will be here. Currently this is only used for the exception
         raised by a failed format checker in :meth:`FormatChecker.check`.
 
+    .. attribute:: parent
+
+        A validation error which this error is the :attr:`context` of.
+        ``None`` if there wasn't one.
+
 
 In case an invalid schema itself is encountered, a :exc:`SchemaError` is
 raised.
diff --git a/jsonschema/exceptions.py b/jsonschema/exceptions.py
index 5979eff..ec9f521 100644
--- a/jsonschema/exceptions.py
+++ b/jsonschema/exceptions.py
@@ -1,4 +1,4 @@
-import collections
+from collections import defaultdict, deque
 import itertools
 import pprint
 import textwrap
@@ -15,18 +15,31 @@ _unset = _utils.Unset()
 
 class _Error(Exception):
     def __init__(
-        self, message, validator=_unset, path=(), cause=None, context=(),
-        validator_value=_unset, instance=_unset, schema=_unset, schema_path=(),
+        self,
+        message,
+        validator=_unset,
+        path=(),
+        cause=None,
+        context=(),
+        validator_value=_unset,
+        instance=_unset,
+        schema=_unset,
+        schema_path=(),
+        parent=None,
     ):
         self.message = message
-        self.path = collections.deque(path)
-        self.schema_path = collections.deque(schema_path)
+        self.path = self.relative_path = deque(path)
+        self.schema_path = self.relative_schema_path = deque(schema_path)
         self.context = list(context)
         self.cause = self.__cause__ = cause
         self.validator = validator
         self.validator_value = validator_value
         self.instance = instance
         self.schema = schema
+        self.parent = parent
+
+        for error in context:
+            error.parent = self
 
     def __repr__(self):
         return "<%s: %r>" % (self.__class__.__name__, self.message)
@@ -40,9 +53,6 @@ class _Error(Exception):
         ):
             return self.message
 
-        path = _utils.format_as_index(self.path)
-        schema_path = _utils.format_as_index(list(self.schema_path)[:-1])
-
         pschema = pprint.pformat(self.schema, width=72)
         pinstance = pprint.pformat(self.instance, width=72)
         return self.message + textwrap.dedent("""
@@ -55,9 +65,9 @@ class _Error(Exception):
             """.rstrip()
         ) % (
             self.validator,
-            schema_path,
+            _utils.format_as_index(list(self.relative_schema_path)[:-1]),
             _utils.indent(pschema),
-            path,
+            _utils.format_as_index(self.relative_path),
             _utils.indent(pinstance),
         )
 
@@ -68,18 +78,37 @@ class _Error(Exception):
     def create_from(cls, other):
         return cls(**other._contents())
 
+    @property
+    def absolute_path(self):
+        parent = self.parent
+        if parent is None:
+            return self.relative_path
+
+        path = deque(self.relative_path)
+        path.extendleft(parent.absolute_path)
+        return path
+
+    @property
+    def absolute_schema_path(self):
+        parent = self.parent
+        if parent is None:
+            return self.relative_schema_path
+
+        path = deque(self.relative_schema_path)
+        path.extendleft(parent.absolute_schema_path)
+        return path
+
     def _set(self, **kwargs):
         for k, v in iteritems(kwargs):
             if getattr(self, k) is _unset:
                 setattr(self, k, v)
 
     def _contents(self):
-        return dict(
-            (attr, getattr(self, attr)) for attr in (
-                "message", "cause", "context", "path", "schema_path",
-                "validator", "validator_value", "instance", "schema"
-            )
+        attrs = (
+            "message", "cause", "context", "validator", "validator_value",
+            "path", "schema_path", "instance", "schema", "parent",
         )
+        return dict((attr, getattr(self, attr)) for attr in attrs)
 
 
 class ValidationError(_Error):
@@ -146,7 +175,7 @@ class ErrorTree(object):
 
     def __init__(self, errors=()):
         self.errors = {}
-        self._contents = collections.defaultdict(self.__class__)
+        self._contents = defaultdict(self.__class__)
 
         for error in errors:
             container = self
diff --git a/jsonschema/tests/test_validators.py b/jsonschema/tests/test_validators.py
index 80db3a7..f88ef51 100644
--- a/jsonschema/tests/test_validators.py
+++ b/jsonschema/tests/test_validators.py
@@ -294,29 +294,55 @@ class TestValidationErrorDetails(unittest.TestCase):
         e = errors[0]
 
         self.assertEqual(e.validator, "anyOf")
-        self.assertEqual(e.schema_path, deque(["anyOf"]))
         self.assertEqual(e.validator_value, schema["anyOf"])
         self.assertEqual(e.instance, instance)
         self.assertEqual(e.schema, schema)
+        self.assertIsNone(e.parent)
+
         self.assertEqual(e.path, deque([]))
+        self.assertEqual(e.relative_path, deque([]))
+        self.assertEqual(e.absolute_path, deque([]))
+
+        self.assertEqual(e.schema_path, deque(["anyOf"]))
+        self.assertEqual(e.relative_schema_path, deque(["anyOf"]))
+        self.assertEqual(e.absolute_schema_path, deque(["anyOf"]))
+
         self.assertEqual(len(e.context), 2)
 
         e1, e2 = sorted_errors(e.context)
 
         self.assertEqual(e1.validator, "minimum")
-        self.assertEqual(e1.schema_path, deque([0, "minimum"]))
         self.assertEqual(e1.validator_value, schema["anyOf"][0]["minimum"])
         self.assertEqual(e1.instance, instance)
         self.assertEqual(e1.schema, schema["anyOf"][0])
+        self.assertIs(e1.parent, e)
+
         self.assertEqual(e1.path, deque([]))
-        self.assertEqual(len(e1.context), 0)
+        self.assertEqual(e1.absolute_path, deque([]))
+        self.assertEqual(e1.relative_path, deque([]))
+
+        self.assertEqual(e1.schema_path, deque([0, "minimum"]))
+        self.assertEqual(e1.relative_schema_path, deque([0, "minimum"]))
+        self.assertEqual(
+            e1.absolute_schema_path, deque(["anyOf", 0, "minimum"]),
+        )
+
+        self.assertFalse(e1.context)
 
         self.assertEqual(e2.validator, "type")
-        self.assertEqual(e2.schema_path, deque([1, "type"]))
         self.assertEqual(e2.validator_value, schema["anyOf"][1]["type"])
         self.assertEqual(e2.instance, instance)
         self.assertEqual(e2.schema, schema["anyOf"][1])
+        self.assertIs(e2.parent, e)
+
         self.assertEqual(e2.path, deque([]))
+        self.assertEqual(e2.relative_path, deque([]))
+        self.assertEqual(e2.absolute_path, deque([]))
+
+        self.assertEqual(e2.schema_path, deque([1, "type"]))
+        self.assertEqual(e2.relative_schema_path, deque([1, "type"]))
+        self.assertEqual(e2.absolute_schema_path, deque(["anyOf", 1, "type"]))
+
         self.assertEqual(len(e2.context), 0)
 
     def test_type(self):
@@ -339,36 +365,61 @@ class TestValidationErrorDetails(unittest.TestCase):
         e = errors[0]
 
         self.assertEqual(e.validator, "type")
-        self.assertEqual(e.schema_path, deque(["type"]))
         self.assertEqual(e.validator_value, schema["type"])
         self.assertEqual(e.instance, instance)
         self.assertEqual(e.schema, schema)
+        self.assertIsNone(e.parent)
+
         self.assertEqual(e.path, deque([]))
+        self.assertEqual(e.relative_path, deque([]))
+        self.assertEqual(e.absolute_path, deque([]))
+
+        self.assertEqual(e.schema_path, deque(["type"]))
+        self.assertEqual(e.relative_schema_path, deque(["type"]))
+        self.assertEqual(e.absolute_schema_path, deque(["type"]))
+
         self.assertEqual(len(e.context), 2)
 
         e1, e2 = sorted_errors(e.context)
 
         self.assertEqual(e1.validator, "type")
-        self.assertEqual(e1.schema_path, deque([0, "type"]))
         self.assertEqual(e1.validator_value, schema["type"][0]["type"])
         self.assertEqual(e1.instance, instance)
         self.assertEqual(e1.schema, schema["type"][0])
+        self.assertIs(e1.parent, e)
+
         self.assertEqual(e1.path, deque([]))
-        self.assertEqual(len(e1.context), 0)
+        self.assertEqual(e1.relative_path, deque([]))
+        self.assertEqual(e1.absolute_path, deque([]))
+
+        self.assertEqual(e1.schema_path, deque([0, "type"]))
+        self.assertEqual(e1.relative_schema_path, deque([0, "type"]))
+        self.assertEqual(e1.absolute_schema_path, deque(["type", 0, "type"]))
+
+        self.assertFalse(e1.context)
 
         self.assertEqual(e2.validator, "enum")
+        self.assertEqual(e2.validator_value, [2])
+        self.assertEqual(e2.instance, 1)
+        self.assertEqual(e2.schema, {u"enum" : [2]})
+        self.assertIs(e2.parent, e)
+
+        self.assertEqual(e2.path, deque(["foo"]))
+        self.assertEqual(e2.relative_path, deque(["foo"]))
+        self.assertEqual(e2.absolute_path, deque(["foo"]))
+
         self.assertEqual(
-            list(e2.schema_path),
-            [1, "properties", "foo", "enum"]
+            e2.schema_path, deque([1, "properties", "foo", "enum"]),
         )
         self.assertEqual(
-            e2.validator_value,
-            schema["type"][1]["properties"]["foo"]["enum"]
+            e2.relative_schema_path, deque([1, "properties", "foo", "enum"]),
         )
-        self.assertEqual(e2.instance, instance["foo"])
-        self.assertEqual(e2.schema, schema["type"][1]["properties"]["foo"])
-        self.assertEqual(e2.path, deque(["foo"]))
-        self.assertEqual(len(e2.context), 0)
+        self.assertEqual(
+            e2.absolute_schema_path,
+            deque(["type", 1, "properties", "foo", "enum"]),
+        )
+
+        self.assertFalse(e2.context)
 
     def test_single_nesting(self):
         instance = {"foo" : 2, "bar" : [1], "baz" : 15, "quux" : "spam"}
@@ -389,6 +440,16 @@ class TestValidationErrorDetails(unittest.TestCase):
         self.assertEqual(e3.path, deque(["baz"]))
         self.assertEqual(e4.path, deque(["foo"]))
 
+        self.assertEqual(e1.relative_path, deque(["bar"]))
+        self.assertEqual(e2.relative_path, deque(["baz"]))
+        self.assertEqual(e3.relative_path, deque(["baz"]))
+        self.assertEqual(e4.relative_path, deque(["foo"]))
+
+        self.assertEqual(e1.absolute_path, deque(["bar"]))
+        self.assertEqual(e2.absolute_path, deque(["baz"]))
+        self.assertEqual(e3.absolute_path, deque(["baz"]))
+        self.assertEqual(e4.absolute_path, deque(["foo"]))
+
         self.assertEqual(e1.validator, "minItems")
         self.assertEqual(e2.validator, "enum")
         self.assertEqual(e3.validator, "maximum")