Re-enable "auto late includes" based on a preliminary directive. We have the...

Re-enable "auto late includes" based on a preliminary directive. We have the feature, so allowing its use won't hurt, as long as users are aware that they will have to change their code later.
See #2079.

Cython/Compiler/Code.py

@@ -155,7 +155,7 @@ class IncludeCode(object):
 
         if initial:
             self.location = self.INITIAL
-        elif False and late:
+        elif late:
             self.location = self.LATE
         else:
             self.location = self.EARLY

Cython/Compiler/Nodes.py

@@ -485,7 +485,9 @@ class CDefExternNode(StatNode):
         if self.include_file or self.verbatim_include:
             # Determine whether include should be late
             stats = self.body.stats
-            if not stats:
+            if not env.directives['preliminary_late_includes_cy28']:
+                late = False
+            elif not stats:
                 # Special case: empty 'cdef extern' blocks are early
                 late = False
             else:

Cython/Compiler/Options.py

@@ -171,6 +171,7 @@ _directive_defaults = {
     'language_level': 2,
     'fast_getattr': False, # Undocumented until we come up with a better way to handle this everywhere.
     'py2_import': False, # For backward compatibility of Cython's source code in Py3 source mode
+    'preliminary_late_includes_cy28': False,  # Temporary directive in 0.28, to be removed in a later version (see GH#2079).
     'iterable_coroutine': False,  # Make async coroutines backwards compatible with the old asyncio yield-from syntax.
     'c_string_type': 'bytes',
     'c_string_encoding': '',

tests/bugs.txt

@@ -16,9 +16,6 @@ cimport_alias_subclass
 # PEP-489 is currently disabled
 run.mod__spec__
 
-# Late includes are currently disabled
-run.extern_include_order
-
 # CPython regression tests that don't current work:
 pyregr.test_signal
 pyregr.test_capi

tests/run/extern_include_order.srctree

@@ -12,6 +12,7 @@ setup(
 )
 
 ######## a.pxd ########
+# cython: preliminary_late_includes_cy28=True
 
 cdef extern from "a_early.h":
   ctypedef int my_int