Optimise "range(enum)" (currently infers enum type for loop variable - worth reconsidering).

CHANGES.rst

@@ -31,6 +31,8 @@ Features added
 Bugs fixed
 ----------
 
+* Loops over ``range(enum)`` were not converted into C for-loops.
+
 * Compile time ``DEF`` assignments were evaluated even when they occur inside of
   falsy ``IF`` blocks. (Github issue #1796)
 

Cython/Compiler/Optimize.py

@@ -259,7 +259,7 @@ class IterationTransform(Visitor.EnvTransform):
                 return self._transform_reversed_iteration(node, iterator)
 
         # range() iteration?
-        if Options.convert_range and node.target.type.is_int:
+        if Options.convert_range and (node.target.type.is_int or node.target.type.is_enum):
             if iterator.self is None and function.is_name and \
                    function.entry and function.entry.is_builtin and \
                    function.name in ('range', 'xrange'):

tests/run/for_in_range_T372.pyx

@@ -117,3 +117,23 @@ def test_return():
             return i,n
     print
     return "FAILED!"
+
+
+ctypedef enum RangeEnum:
+    EnumValue1
+    EnumValue2
+    EnumValue3
+
+
+@cython.test_assert_path_exists("//ForFromStatNode")
+@cython.test_fail_if_path_exists("//ForInStatNode")
+def test_enum_range():
+    """
+    # NOTE: it's not entirely clear that this is the expected behaviour, but that's how it currently is.
+    >>> test_enum_range()
+    'RangeEnum'
+    """
+    cdef RangeEnum n = EnumValue3
+    for i in range(n):
+        assert cython.typeof(i) == "RangeEnum", cython.typeof(i)
+    return cython.typeof(i)