Add a new error, 'nonlocal-and-global'.

This error is emitted when a name is found to be both nonlocal and global in the same scope.
This is a SyntaxError in Python 2, but Python 3's ast happily parses it, so it needs
to be a separate error. Closes issue #581.

5 files changed, 40 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 5c9eb39..bd23848 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -209,6 +209,10 @@ ChangeLog for Pylint
       These were moved since they didn't belong in astroid.
 
     * Enable misplaced-future for Python 3. Closes issue #580.
+
+    * Add a new error, 'nonlocal-and-global', which is emitted when a
+      name is found to be both nonlocal and global in the same scope.
+      Closes issue #581.
       
 
 
diff --git a/pylint/checkers/base.py b/pylint/checkers/base.py
index f2d2969..2ef4b8f 100644
--- a/pylint/checkers/base.py
+++ b/pylint/checkers/base.py
@@ -322,6 +322,10 @@ class BasicErrorChecker(_BasicChecker):
                   'Emitted when a star expression is not used in an '
                   'assignment target.',
                   {'minversion': (3, 0)}),
+        'E0115': ('Name %r is nonlocal and global',
+                  'nonlocal-and-global',
+                  'Emitted when a name is both nonlocal and global.',
+                  {'minversion': (3, 0)}),
         }
 
     @check_messages('function-redefined')
@@ -351,8 +355,9 @@ class BasicErrorChecker(_BasicChecker):
 
     @check_messages('init-is-generator', 'return-in-init',
                     'function-redefined', 'return-arg-in-generator',
-                    'duplicate-argument-name')
+                    'duplicate-argument-name', 'nonlocal-and-global')
     def visit_function(self, node):
+        self._check_nonlocal_and_global(node)
         if not redefined_by_decorator(node):
             self._check_redefinition(node.is_method() and 'method' or 'function', node)
         # checks for max returns, branch, return in __init__
@@ -386,6 +391,21 @@ class BasicErrorChecker(_BasicChecker):
             else:
                 args.add(name)
 
+    def _check_nonlocal_and_global(self, node):
+        """Check that a name is both nonlocal and global."""
+        def same_scope(current):
+            return current.scope() is node
+
+        from_iter = itertools.chain.from_iterable
+        nonlocals = set(from_iter(
+            child.names for child in node.nodes_of_class(astroid.Nonlocal)
+            if same_scope(child)))
+        global_vars = set(from_iter(
+            child.names for child in node.nodes_of_class(astroid.Global)
+            if same_scope(child)))
+        for name in nonlocals.intersection(global_vars):
+            self.add_message('nonlocal-and-global',
+                             args=(name, ), node=node)
 
     @check_messages('return-outside-function')
     def visit_return(self, node):
diff --git a/pylint/test/functional/nonlocal_and_global.py b/pylint/test/functional/nonlocal_and_global.py
new file mode 100644
index 0000000..c601a29
--- /dev/null
+++ b/pylint/test/functional/nonlocal_and_global.py
@@ -0,0 +1,12 @@
+"""Test that a name is both nonlocal and global in the same scope."""

+# pylint: disable=missing-docstring,global-variable-not-assigned,invalid-name

+

+def bad(): # [nonlocal-and-global]

+    nonlocal missing

+    global missing

+

+def good():

+    nonlocal missing

+    def test():

+        global missing

+    return test

diff --git a/pylint/test/functional/nonlocal_and_global.rc b/pylint/test/functional/nonlocal_and_global.rc
new file mode 100644
index 0000000..c093be2
--- /dev/null
+++ b/pylint/test/functional/nonlocal_and_global.rc
@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.0
diff --git a/pylint/test/functional/nonlocal_and_global.txt b/pylint/test/functional/nonlocal_and_global.txt
new file mode 100644
index 0000000..46f0d0f
--- /dev/null
+++ b/pylint/test/functional/nonlocal_and_global.txt
@@ -0,0 +1 @@
+nonlocal-and-global:4:bad:"Name 'missing' is nonlocal and global"
\ No newline at end of file