Report assert using tuple

This is a SyntaxWarning on Python 2.6+

Resolves lp:848467

Author: jayvdb

pyflakes/checker.py

@@ -671,7 +671,7 @@ def ignore(self, node):
 
     # "stmt" type nodes
     DELETE = PRINT = FOR = ASYNCFOR = WHILE = IF = WITH = WITHITEM = \
-        ASYNCWITH = ASYNCWITHITEM = RAISE = TRYFINALLY = ASSERT = EXEC = \
+        ASYNCWITH = ASYNCWITHITEM = RAISE = TRYFINALLY = EXEC = \
         EXPR = ASSIGN = handleChildren
 
     PASS = ignore
@@ -697,6 +697,11 @@ def ignore(self, node):
     # additional node types
     COMPREHENSION = KEYWORD = FORMATTEDVALUE = handleChildren
 
+    def ASSERT(self, node):
+        if isinstance(node.test, ast.Tuple) and node.test.elts != []:
+            self.report(messages.AssertTuple, node)
+        self.handleChildren(node)
+
     def GLOBAL(self, node):
         """
         Keep track of globals declarations.

pyflakes/messages.py

@@ -191,3 +191,10 @@ class TooManyExpressionsInStarredAssignment(Message):
     Too many expressions in an assignment with star-unpacking
     """
     message = 'too many expressions in star-unpacking assignment'
+
+
+class AssertTuple(Message):
+    """
+    Assertion test is a tuple, which are always True.
+    """
+    message = 'assertion is always true, perhaps remove parentheses?'

pyflakes/test/test_other.py

@@ -1633,6 +1633,40 @@ def test_augmentedAssignmentImportedFunctionCall(self):
         baz += bar()
         ''')
 
+    def test_assert_without_message(self):
+        """An assert without a message is not an error."""
+        self.flakes('''
+        a = 1
+        assert a
+        ''')
+
+    def test_assert_with_message(self):
+        """An assert with a message is not an error."""
+        self.flakes('''
+        a = 1
+        assert a, 'x'
+        ''')
+
+    def test_assert_tuple(self):
+        """An assert of a non-empty tuple is always True."""
+        self.flakes('''
+        assert (False, 'x')
+        assert (False, )
+        ''', m.AssertTuple, m.AssertTuple)
+
+    def test_assert_tuple_empty(self):
+        """An assert of an empty tuple is always False."""
+        self.flakes('''
+        assert ()
+        ''')
+
+    def test_assert_static(self):
+        """An assert of a static value is not an error."""
+        self.flakes('''
+        assert True
+        assert 1
+        ''')
+
     @skipIf(version_info < (3, 3), 'new in Python 3.3')
     def test_yieldFromUndefined(self):
         """