1 files changed, 55 insertions, 29 deletions
diff --git a/generator/google/protobuf/internal/api_implementation.py b/generator/google/protobuf/internal/api_implementation.py
index ce02a32..460a4a6 100644
--- a/generator/google/protobuf/internal/api_implementation.py
+++ b/generator/google/protobuf/internal/api_implementation.py
@@ -1,6 +1,6 @@
 # Protocol Buffers - Google's data interchange format
 # Copyright 2008 Google Inc.  All rights reserved.
-# http://code.google.com/p/protobuf/
+# https://developers.google.com/protocol-buffers/
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
@@ -28,53 +28,78 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+"""Determine which implementation of the protobuf API is used in this process.
 """
-This module is the central entity that determines which implementation of the
-API is used.
-"""
-
-__author__ = 'petar@google.com (Petar Petrov)'
 
 import os
+import warnings
+import sys
+
+try:
+  # pylint: disable=g-import-not-at-top
+  from google.protobuf.internal import _api_implementation
+  # The compile-time constants in the _api_implementation module can be used to
+  # switch to a certain implementation of the Python API at build time.
+  _api_version = _api_implementation.api_version
+  _proto_extension_modules_exist_in_build = True
+except ImportError:
+  _api_version = -1  # Unspecified by compiler flags.
+  _proto_extension_modules_exist_in_build = False
+
+if _api_version == 1:
+  raise ValueError('api_version=1 is no longer supported.')
+if _api_version < 0:  # Still unspecified?
+  try:
+    # The presence of this module in a build allows the proto implementation to
+    # be upgraded merely via build deps rather than a compiler flag or the
+    # runtime environment variable.
+    # pylint: disable=g-import-not-at-top
+    from google.protobuf import _use_fast_cpp_protos
+    # Work around a known issue in the classic bootstrap .par import hook.
+    if not _use_fast_cpp_protos:
+      raise ImportError('_use_fast_cpp_protos import succeeded but was None')
+    del _use_fast_cpp_protos
+    _api_version = 2
+  except ImportError:
+    if _proto_extension_modules_exist_in_build:
+      if sys.version_info[0] >= 3:  # Python 3 defaults to C++ impl v2.
+        _api_version = 2
+      # TODO(b/17427486): Make Python 2 default to C++ impl v2.
+
+_default_implementation_type = (
+    'python' if _api_version <= 0 else 'cpp')
+
 # This environment variable can be used to switch to a certain implementation
-# of the Python API. Right now only 'python' and 'cpp' are valid values. Any
-# other value will be ignored.
+# of the Python API, overriding the compile-time constants in the
+# _api_implementation module. Right now only 'python' and 'cpp' are valid
+# values. Any other value will be ignored.
 _implementation_type = os.getenv('PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION',
-                                 'python')
-
+                                 _default_implementation_type)
 
 if _implementation_type != 'python':
-  # For now, by default use the pure-Python implementation.
-  # The code below checks if the C extension is available and
-  # uses it if it is available.
   _implementation_type = 'cpp'
-  ## Determine automatically which implementation to use.
-  #try:
-  #  from google.protobuf.internal import cpp_message
-  #  _implementation_type = 'cpp'
-  #except ImportError, e:
-  #  _implementation_type = 'python'
 
+if 'PyPy' in sys.version and _implementation_type == 'cpp':
+  warnings.warn('PyPy does not work yet with cpp protocol buffers. '
+                'Falling back to the python implementation.')
+  _implementation_type = 'python'
 
 # This environment variable can be used to switch between the two
-# 'cpp' implementations. Right now only 1 and 2 are valid values. Any
-# other value will be ignored.
+# 'cpp' implementations, overriding the compile-time constants in the
+# _api_implementation module. Right now only '2' is supported. Any other
+# value will cause an error to be raised.
 _implementation_version_str = os.getenv(
-    'PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION',
-    '1')
-
+    'PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION', '2')
 
-if _implementation_version_str not in ('1', '2'):
+if _implementation_version_str != '2':
   raise ValueError(
-      "unsupported PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION: '" +
-      _implementation_version_str + "' (supported versions: 1, 2)"
+      'unsupported PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION: "' +
+      _implementation_version_str + '" (supported versions: 2)'
       )
 
-
 _implementation_version = int(_implementation_version_str)
 
 
-
 # Usage of this function is discouraged. Clients shouldn't care which
 # implementation of the API is in use. Note that there is no guarantee
 # that differences between APIs will be maintained.
@@ -82,6 +107,7 @@ _implementation_version = int(_implementation_version_str)
 def Type():
   return _implementation_type
 
+
 # See comment on 'Type' above.
 def Version():
   return _implementation_version