Add structured exceptions to decorators and remaining functions.

* Use explicit StopIteration to pass information from generators to
  raise_if_nothing_inferred and path_wrapper, rather than return or
  implicit termination by reaching the end of the code block.

* Remove remove_nodes in favor of handling the cases in local_attr,
  istance_attr, and getattr, to avoid the need for complicated
  information passing when needing to raise an exception.

5 files changed, 112 insertions, 82 deletions

diff --git a/astroid/decorators.py b/astroid/decorators.py
index 815b540..e60eb49 100644
--- a/astroid/decorators.py
+++ b/astroid/decorators.py
@@ -93,15 +93,26 @@ def path_wrapper(func):
             return
 
         yielded = set()
-        for res in _func(node, context, **kwargs):
-            # unproxy only true instance, not const, tuple, dict...
-            if res.__class__.__name__ == 'Instance':
-                ares = res._proxied
+        generator = _func(node, context, **kwargs)
+        try:
+            while True:
+                res = next(generator)
+                # unproxy only true instance, not const, tuple, dict...
+                if res.__class__.__name__ == 'Instance':
+                    ares = res._proxied
+                else:
+                    ares = res
+                if ares not in yielded:
+                    yield res
+                    yielded.add(ares)
+        except StopIteration as error:
+            # Explicit StopIteration to return error information, see
+            # comment in raise_if_nothing_inferred.
+            if len(error.args) > 0:
+                util.reraise(StopIteration(error.args[0]))
             else:
-                ares = res
-            if ares not in yielded:
-                yield res
-                yielded.add(ares)
+                util.reraise(StopIteration())
+
     return wrapped
 
 
@@ -117,18 +128,32 @@ def yes_if_nothing_inferred(func, instance, args, kwargs):
 
 @wrapt.decorator
 def raise_if_nothing_inferred(func, instance, args, kwargs):
-    '''All generators wrapped with raise_if_nothing_inferred *must* raise
-    exceptions.DefaultStop if they can terminate without output, to
-    propagate error information.
+    '''All generators wrapped with raise_if_nothing_inferred *must*
+    explicitly raise StopIteration with information to create an
+    appropriate structured InferenceError.
+
     '''
+    # TODO: Explicitly raising StopIteration in a generator will cause
+    # a RuntimeError in Python >=3.7, as per
+    # http://legacy.python.org/dev/peps/pep-0479/ .  Before 3.7 is
+    # released, this code will need to use one of four possible
+    # solutions: a decorator that restores the current behavior as
+    # described in
+    # http://legacy.python.org/dev/peps/pep-0479/#sub-proposal-decorator-to-explicitly-request-current-behaviour
+    # , dynamic imports or exec to generate different code for
+    # different versions, drop support for all Python versions <3.3,
+    # or refactoring to change how these decorators work.  In any
+    # event, after dropping support for Python <3.3 this code should
+    # be refactored to use `yield from`.
     inferred = False
-    fields = {}
     try:
-        for node in func(*args, **kwargs):
+        generator = func(*args, **kwargs)
+        while True:
+            yield next(generator)
             inferred = True
-            yield node
-    except exceptions.DefaultStop as e:
-        fields = vars(e)
-        del fields['message']
-    if not inferred:
-        raise exceptions.InferenceError(**fields)
+    except StopIteration as error:
+        if not inferred:
+            if len(error.args) > 0:
+                util.reraise(exceptions.InferenceError(**error.args[0]))
+            else:
+                util.reraise(exceptions.InferenceError())
diff --git a/astroid/exceptions.py b/astroid/exceptions.py
index 9f49753..ede21d9 100644
--- a/astroid/exceptions.py
+++ b/astroid/exceptions.py
@@ -69,18 +69,6 @@ class NoDefault(AstroidError):
         super(NoDefault, self).__init__(message, **kws)
 
 
-class DefaultStop(AstroidError):
-    '''This is a special error that's only meant to be raised in
-    generators wrapped with raise_if_nothing_inferred and
-    yes_if_nothing_inferred.  It does nothing other than carry a set
-    of attributes to be used in raising in InferenceError.
-
-    '''
-    
-    # def __init__(self, message='{func!r} has no default for {name!r}.', **kws):
-    #     super(NoDefault, self).__init__(message, **kws)
-
-
 class ResolveError(AstroidError):
     """Base class of astroid resolution/inference error.
 
diff --git a/astroid/inference.py b/astroid/inference.py
index b5e45df..fda4546 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -118,7 +118,9 @@ def infer_call(self, context=None):
         except exceptions.InferenceError:
             ## XXX log error ?
             continue
-    raise exceptions.DefaultStop(node=self, context=context)
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, context=context))
 nodes.Call._infer = infer_call
 
 
@@ -179,7 +181,9 @@ def infer_attribute(self, context=None):
         except AttributeError:
             # XXX method / function
             context.boundnode = None
-    raise exceptions.DefaultStop(node=self, context=context)
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, context=context))
 nodes.Attribute._infer = decorators.path_wrapper(infer_attribute)
 nodes.AssignAttr.infer_lhs = infer_attribute # # won't work with a path wrapper
 
@@ -282,7 +286,9 @@ def infer_subscript(self, context=None):
     for inferred in assigned.infer(context):
         yield inferred
 
-    raise exceptions.DefaultStop(node=self, context=context)
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, context=context))
 
 nodes.Subscript._infer = decorators.path_wrapper(infer_subscript)
 nodes.Subscript.infer_lhs = infer_subscript
@@ -338,7 +344,9 @@ def _infer_boolop(self, context=None):
         else:
             yield value
 
-    raise exceptions.DefaultStop(node=self, context=context)
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, context=context))
 
 nodes.BoolOp._infer = _infer_boolop
 
@@ -411,7 +419,9 @@ def infer_unaryop(self, context=None):
     for inferred in _filter_operation_errors(self, _infer_unaryop, context,
                                              util.BadUnaryOperationMessage):
         yield inferred
-    raise exceptions.DefaultStop(node=self, context=context)
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, context=context))
 
 nodes.UnaryOp._infer_unaryop = _infer_unaryop
 nodes.UnaryOp._infer = infer_unaryop
@@ -728,11 +738,15 @@ def instance_getitem(self, index, context=None):
 
     method = next(self.igetattr('__getitem__', context=context))
     if not isinstance(method, bases.BoundMethod):
-        raise exceptions.InferenceError(node=self, context=context)
+        raise exceptions.InferenceError(
+            'Could not find __getitem__ for {node!r}.',
+            node=self, context=context)
 
     try:
         return next(method.infer_call_result(self, new_context))
     except StopIteration:
-        util.reraise(exceptions.InferenceError(node=self, context=context))
+        util.reraise(exceptions.InferenceError(
+            message='Inference for {node!r}[{index!s}] failed.',
+            node=self, index=index.value, context=context))
 
 bases.Instance.getitem = instance_getitem
diff --git a/astroid/protocols.py b/astroid/protocols.py
index 2e01124..5809e4a 100644
--- a/astroid/protocols.py
+++ b/astroid/protocols.py
@@ -249,9 +249,10 @@ def for_assigned_stmts(self, node, context=None, asspath=None):
         for inferred in _resolve_looppart(self.iter.infer(context),
                                           asspath, context):
             yield inferred
-    raise exceptions.DefaultStop(node=self, unknown=node,
-                                 assign_path=asspath, context=context)
-
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, unknown=node,
+                             assign_path=asspath, context=context))
 
 nodes.For.assigned_stmts = for_assigned_stmts
 nodes.Comprehension.assigned_stmts = for_assigned_stmts
@@ -337,8 +338,10 @@ def assign_assigned_stmts(self, node, context=None, asspath=None):
         return
     for inferred in _resolve_asspart(self.value.infer(context), asspath, context):
         yield inferred
-    raise exceptions.DefaultStop(node=self, unknown=node,
-                                 assign_path=asspath, context=context)
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, unknown=node,
+                             assign_path=asspath, context=context))
 
 nodes.Assign.assigned_stmts = assign_assigned_stmts
 nodes.AugAssign.assigned_stmts = assign_assigned_stmts
@@ -379,9 +382,11 @@ def excepthandler_assigned_stmts(self, node, context=None, asspath=None):
         if isinstance(assigned, nodes.ClassDef):
             assigned = bases.Instance(assigned)
         yield assigned
-    raise exceptions.DefaultStop(node=self, unknown=node,
-                                 assign_path=asspath, context=context)        
-        
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, unknown=node,
+                             assign_path=asspath, context=context))
+
 
 nodes.ExceptHandler.assigned_stmts = excepthandler_assigned_stmts
 
@@ -479,8 +484,10 @@ def with_assigned_stmts(self, node, context=None, asspath=None):
                         'in {node!r}.', node=self, targets=node,
                         assign_path=asspath, context=context))
             yield obj
-    raise exceptions.DefaultStop(node=self, unknown=node,
-                                 assign_path=asspath, context=context)        
+    # Explicit StopIteration to return error information, see comment
+    # in raise_if_nothing_inferred.
+    raise StopIteration(dict(node=self, unknown=node,
+                             assign_path=asspath, context=context))
 
 nodes.With.assigned_stmts = with_assigned_stmts
 
diff --git a/astroid/scoped_nodes.py b/astroid/scoped_nodes.py
index 3b1e18a..4f5e39d 100644
--- a/astroid/scoped_nodes.py
+++ b/astroid/scoped_nodes.py
@@ -86,20 +86,6 @@ def _verify_duplicates_mro(sequences, cls, context):
                 mros=sequences, cls=cls, context=context)
 
 
-def remove_nodes(cls):
-    @wrapt.decorator
-    def decorator(func, instance, args, kwargs):
-        nodes = [n for n in func(*args, **kwargs) if not isinstance(n, cls)]
-        if not nodes:
-            # TODO: no way to access the context when raising this error.
-            raise exceptions.AttributeInferenceError(
-                'No nodes left after removing all {remove_type!r} from '
-                'nodes inferred for {node!r}.',
-                node=instance, remove_type=cls)
-        return nodes
-    return decorator
-
-
 def function_to_method(n, klass):
     if isinstance(n, FunctionDef):
         if n.type == 'classmethod':
@@ -359,23 +345,28 @@ class Module(LocalsDictNodeNG):
     def display_type(self):
         return 'Module'
 
-    @remove_nodes(node_classes.DelName)
     def getattr(self, name, context=None, ignore_locals=False):
+        result = []
         if name in self.special_attributes:
             if name == '__file__':
-                return [node_classes.const_factory(self.file)] + self.locals.get(name, [])
-            if name == '__path__' and self.package:
-                return [node_classes.List()] + self.locals.get(name, [])
-            return std_special_attributes(self, name)
-        if not ignore_locals and name in self.locals:
-            return self.locals[name]
-        if self.package:
+                result = ([node_classes.const_factory(self.file)] +
+                          self.locals.get(name, []))
+            elif name == '__path__' and self.package:
+                result = [node_classes.List()] + self.locals.get(name, [])
+            else:
+                result = std_special_attributes(self, name)
+        elif not ignore_locals and name in self.locals:
+            result = self.locals[name]
+        elif self.package:
             try:
-                return [self.import_module(name, relative_only=True)]
+                result = [self.import_module(name, relative_only=True)]
             except (exceptions.AstroidBuildingException, SyntaxError):
                 util.reraise(exceptions.AttributeInferenceError(target=self,
                                                                 attribute=name,
                                                                 context=context))
+        result = [n for n in result if not isinstance(n, node_classes.DelName)]
+        if result:
+            return result
         raise exceptions.AttributeInferenceError(target=self, attribute=name,
                                                  context=context)
 
@@ -1311,7 +1302,6 @@ class ClassDef(mixins.FilterStmtsMixin, LocalsDictNodeNG,
     def has_base(self, node):
         return node in self.bases
 
-    @remove_nodes(node_classes.DelAttr)
     def local_attr(self, name, context=None):
         """return the list of assign node associated to name in this class
         locals or in its parents
@@ -1320,15 +1310,20 @@ class ClassDef(mixins.FilterStmtsMixin, LocalsDictNodeNG,
           if no attribute with this name has been find in this class or
           its parent classes
         """
-        try:
-            return self.locals[name]
-        except KeyError:
-            for class_node in self.local_attr_ancestors(name, context):
-                return class_node.locals[name]
+        result = []
+        if name in self.locals:
+            result = self.locals[name]
+        else:
+            try:
+                result = next(self.local_attr_ancestors(name, context)).locals[name]
+            except StopIteration:
+                pass
+        result = [n for n in result if not isinstance(n, node_classes.DelAttr)]
+        if result:
+            return result
         raise exceptions.AttributeInferenceError(target=self, attribute=name,
                                                  context=context)
 
-    @remove_nodes(node_classes.DelAttr)
     def instance_attr(self, name, context=None):
         """return the astroid nodes associated to name in this class instance
         attributes dictionary and in its parents
@@ -1343,10 +1338,11 @@ class ClassDef(mixins.FilterStmtsMixin, LocalsDictNodeNG,
         # get all values from parents
         for class_node in self.instance_attr_ancestors(name, context):
             values += class_node.instance_attrs[name]
-        if not values:
-            raise exceptions.AttributeInferenceError(target=self, attribute=name,
-                                                     context=context)
-        return values
+        values = [n for n in values if not isinstance(n, node_classes.DelAttr)]
+        if values:
+            return values
+        raise exceptions.AttributeInferenceError(target=self, attribute=name,
+                                                 context=context)
 
     def instanciate_class(self):
         """return Instance of ClassDef node, else return self"""