Add whitespace around -> annotating operator (#809)

* Test for whitespace around -> operator

Tests will pass after fixing issue #803

* Require whitespace around -> operator

Closes: #803

* Move tests to correct cases

* Whitelist python3 only tests

* Fix whitespace test errors

Huge thanks to @asottile!

* Address code review

Pushing this directly to run full testsuite on travis

* 🐛Change error code to space around bitwise operator E227

* Check for -> annotation only in py3.5+

* Skip tests meant for higher versions of python

* Move type annotation tests to python3.5 testsuite

Type annotations were first introduced in PEP 484,https://www.python.org/dev/peps/pep-0484/ implemented in python3.5

* Shorten line skipping tests by version

* Replace test skipping logic

As requested in code review

* Run formatting to avoid long lines

Author: Tadaboody

pycodestyle.py

@@ -115,9 +115,12 @@ def lru_cache(maxsize=128):  # noqa as it's a fake implementation.
 UNARY_OPERATORS = frozenset(['>>', '**', '*', '+', '-'])
 ARITHMETIC_OP = frozenset(['**', '*', '/', '//', '+', '-'])
 WS_OPTIONAL_OPERATORS = ARITHMETIC_OP.union(['^', '&', '|', '<<', '>>', '%'])
+# Warn for -> function annotation operator in py3.5+ (issue 803)
+FUNCTION_RETURN_ANNOTATION_OP = ['->'] if sys.version_info >= (3, 5) else []
 WS_NEEDED_OPERATORS = frozenset([
     '**=', '*=', '/=', '//=', '+=', '-=', '!=', '<>', '<', '>',
-    '%=', '^=', '&=', '|=', '==', '<=', '>=', '<<=', '>>=', '='])
+    '%=', '^=', '&=', '|=', '==', '<=', '>=', '<<=', '>>=', '='] +
+    FUNCTION_RETURN_ANNOTATION_OP)
 WHITESPACE = frozenset(' \t')
 NEWLINE = frozenset([tokenize.NL, tokenize.NEWLINE])
 SKIP_TOKENS = NEWLINE.union([tokenize.INDENT, tokenize.DEDENT])

testsuite/python35.py

@@ -0,0 +1,6 @@
+#: E225
+def bar(a, b)->int:
+    pass
+#: Okay
+def baz(a, b) -> int:
+    pass

testsuite/support.py

@@ -168,6 +168,13 @@ def init_tests(pep8style):
 
     def run_tests(filename):
         """Run all the tests from a file."""
+        # Skip tests meant for higher versions of python
+        ver_match = re.search(r'python(\d)(\d)?\.py$', filename)
+        if ver_match:
+            test_against_version = tuple(int(val or 0)
+                                         for val in ver_match.groups())
+            if sys.version_info < test_against_version:
+                return
         lines = readlines(filename) + ['#:\n']
         line_offset = 0
         codes = ['Okay']