PEP 498 f-strings support

PEP 498 f-strings cause pyflakes to crash with
AttributeError: 'Checker' object has no attribute 'FORMATTEDVALUE'

Author: jayvdb

pyflakes/checker.py

@@ -675,7 +675,7 @@ def ignore(self, node):
         EQ = NOTEQ = LT = LTE = GT = GTE = IS = ISNOT = IN = NOTIN = ignore
 
     # additional node types
-    COMPREHENSION = KEYWORD = handleChildren
+    COMPREHENSION = KEYWORD = FORMATTEDVALUE = handleChildren
 
     def GLOBAL(self, node):
         """

pyflakes/test/test_other.py

@@ -989,6 +989,14 @@ def test_returnOnly(self):
         """Do not crash on lone "return"."""
         self.flakes('return 2')
 
+    @skipIf(version_info < (3, 6), 'new in Python 3.6')
+    def test_f_string(self):
+        """Test PEP 498 f-strings are treated as a usage."""
+        self.flakes('''
+        baz = 0
+        print(f'\x7b4*baz\N{RIGHT CURLY BRACKET}')
+        ''')
+
 
 class TestAsyncStatements(TestCase):