Use __future__.py from CPython.

This version vas features like compiler flags that other libraries use.

Languages/IronPython/IronPython/Lib/__future__.py

@@ -1,25 +1,128 @@
-#####################################################################################
-#
-#  Copyright (c) Microsoft Corporation. All rights reserved.
-#
-# This source code is subject to terms and conditions of the Apache License, Version 2.0. A 
-# copy of the license can be found in the License.html file at the root of this distribution. If 
-# you cannot locate the  Apache License, Version 2.0, please send an email to 
-# [email protected]. By using this source code in any fashion, you are agreeing to be bound 
-# by the terms of the Apache License, Version 2.0.
-#
-# You must not remove this notice, or any other, from this software.
-#
-#
-#####################################################################################
-
-all_feature_names = ['nested_scopes', 'generators', 'division', 
-                     'absolute_import', 'with_statement', 'print_function', 
-                     'unicode_literals']
-
-division=1
-with_statement=1
-generators=1
-absolute_import=1
-print_function=1
-unicode_literals=1
+"""Record of phased-in incompatible language changes.
+
+Each line is of the form:
+
+    FeatureName = "_Feature(" OptionalRelease "," MandatoryRelease ","
+                              CompilerFlag ")"
+
+where, normally, OptionalRelease < MandatoryRelease, and both are 5-tuples
+of the same form as sys.version_info:
+
+    (PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
+     PY_MINOR_VERSION, # the 1; an int
+     PY_MICRO_VERSION, # the 0; an int
+     PY_RELEASE_LEVEL, # "alpha", "beta", "candidate" or "final"; string
+     PY_RELEASE_SERIAL # the 3; an int
+    )
+
+OptionalRelease records the first release in which
+
+    from __future__ import FeatureName
+
+was accepted.
+
+In the case of MandatoryReleases that have not yet occurred,
+MandatoryRelease predicts the release in which the feature will become part
+of the language.
+
+Else MandatoryRelease records when the feature became part of the language;
+in releases at or after that, modules no longer need
+
+    from __future__ import FeatureName
+
+to use the feature in question, but may continue to use such imports.
+
+MandatoryRelease may also be None, meaning that a planned feature got
+dropped.
+
+Instances of class _Feature have two corresponding methods,
+.getOptionalRelease() and .getMandatoryRelease().
+
+CompilerFlag is the (bitfield) flag that should be passed in the fourth
+argument to the builtin function compile() to enable the feature in
+dynamically compiled code.  This flag is stored in the .compiler_flag
+attribute on _Future instances.  These values must match the appropriate
+#defines of CO_xxx flags in Include/compile.h.
+
+No feature line is ever to be deleted from this file.
+"""
+
+all_feature_names = [
+    "nested_scopes",
+    "generators",
+    "division",
+    "absolute_import",
+    "with_statement",
+    "print_function",
+    "unicode_literals",
+]
+
+__all__ = ["all_feature_names"] + all_feature_names
+
+# The CO_xxx symbols are defined here under the same names used by
+# compile.h, so that an editor search will find them here.  However,
+# they're not exported in __all__, because they don't really belong to
+# this module.
+CO_NESTED            = 0x0010   # nested_scopes
+CO_GENERATOR_ALLOWED = 0        # generators (obsolete, was 0x1000)
+CO_FUTURE_DIVISION   = 0x2000   # division
+CO_FUTURE_ABSOLUTE_IMPORT = 0x4000 # perform absolute imports by default
+CO_FUTURE_WITH_STATEMENT  = 0x8000   # with statement
+CO_FUTURE_PRINT_FUNCTION  = 0x10000   # print function
+CO_FUTURE_UNICODE_LITERALS = 0x20000 # unicode string literals
+
+class _Feature:
+    def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):
+        self.optional = optionalRelease
+        self.mandatory = mandatoryRelease
+        self.compiler_flag = compiler_flag
+
+    def getOptionalRelease(self):
+        """Return first release in which this feature was recognized.
+
+        This is a 5-tuple, of the same form as sys.version_info.
+        """
+
+        return self.optional
+
+    def getMandatoryRelease(self):
+        """Return release in which this feature will become mandatory.
+
+        This is a 5-tuple, of the same form as sys.version_info, or, if
+        the feature was dropped, is None.
+        """
+
+        return self.mandatory
+
+    def __repr__(self):
+        return "_Feature" + repr((self.optional,
+                                  self.mandatory,
+                                  self.compiler_flag))
+
+nested_scopes = _Feature((2, 1, 0, "beta",  1),
+                         (2, 2, 0, "alpha", 0),
+                         CO_NESTED)
+
+generators = _Feature((2, 2, 0, "alpha", 1),
+                      (2, 3, 0, "final", 0),
+                      CO_GENERATOR_ALLOWED)
+
+division = _Feature((2, 2, 0, "alpha", 2),
+                    (3, 0, 0, "alpha", 0),
+                    CO_FUTURE_DIVISION)
+
+absolute_import = _Feature((2, 5, 0, "alpha", 1),
+                           (2, 7, 0, "alpha", 0),
+                           CO_FUTURE_ABSOLUTE_IMPORT)
+
+with_statement = _Feature((2, 5, 0, "alpha", 1),
+                          (2, 6, 0, "alpha", 0),
+                          CO_FUTURE_WITH_STATEMENT)
+
+print_function = _Feature((2, 6, 0, "alpha", 2),
+                          (3, 0, 0, "alpha", 0),
+                          CO_FUTURE_PRINT_FUNCTION)
+
+unicode_literals = _Feature((2, 6, 0, "alpha", 2),
+                            (3, 0, 0, "alpha", 0),
+                            CO_FUTURE_UNICODE_LITERALS)