From 42e1e2abef8c49efffaa55c645b04bb7e4184cc8 Mon Sep 17 00:00:00 2001
From: Jie Luo <jieluo@google.com>
Date: Mon, 30 Jan 2017 15:23:35 -0800
Subject: Fix python compatibility test when a new generated code imports an
 old version(2.6.1 or older) generated code.

---
 python/compatibility_tests/v2.5.0/test.sh               | 14 ++++----------
 src/google/protobuf/compiler/python/python_generator.cc | 11 ++++++++++-
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/python/compatibility_tests/v2.5.0/test.sh b/python/compatibility_tests/v2.5.0/test.sh
index c640da80..78c16ad1 100755
--- a/python/compatibility_tests/v2.5.0/test.sh
+++ b/python/compatibility_tests/v2.5.0/test.sh
@@ -92,16 +92,10 @@ python setup.py test
 # Test A.3:
 #   proto set 1: use old version
 #   proto set 2 which may import protos in set 1: use new version
-# Compatiblility test fail if the old verison is less than 3.0.0-alpha-1.
-# Because module name aliases was added in v3.0.0-alpha-1 instead of
-# fully-qualified module names to refer to dependencies: dot was replaced
-# with _dot_.
-if [ "$(printf "$OLD_VERSION\n3.0.0" | sort -V | head -n 1 )" = "3.0.0" ]; then
-  cp old_protoc protoc_1
-  cp ../../../src/protoc protoc_2
-  python setup.py build
-  python setup.py test
-fi
+cp old_protoc protoc_1
+cp ../../../src/protoc protoc_2
+python setup.py build
+python setup.py test
 
 rm google -r -f
 rm build -r -f
diff --git a/src/google/protobuf/compiler/python/python_generator.cc b/src/google/protobuf/compiler/python/python_generator.cc
index f5769128..f83f155a 100644
--- a/src/google/protobuf/compiler/python/python_generator.cc
+++ b/src/google/protobuf/compiler/python/python_generator.cc
@@ -1380,8 +1380,17 @@ void Generator::FixOptionsForMessage(const Descriptor& descriptor) const {
 void Generator::CopyPublicDependenciesAliases(
     const string& copy_from, const FileDescriptor* file) const {
   for (int i = 0; i < file->public_dependency_count(); ++i) {
+    string module_name = ModuleName(file->public_dependency(i)->name());
     string module_alias = ModuleAlias(file->public_dependency(i)->name());
-    printer_->Print("$alias$ = $copy_from$.$alias$\n", "alias", module_alias,
+    // There's no module alias in the dependent file if it was generated by
+    // an old protoc (less than 3.0.0-alpha-1). Use module name in this
+    // situation.
+    printer_->Print("try:\n"
+                    "  $alias$ = $copy_from$.$alias$\n"
+                    "except AttributeError:\n"
+                    "  $alias$ = $copy_from$.$module$\n",
+                    "alias", module_alias,
+                    "module", module_name,
                     "copy_from", copy_from);
     CopyPublicDependenciesAliases(copy_from, file->public_dependency(i));
   }
-- 
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