Fixed a Visual Studio 2017 build error. (#4488)

The current 15.6.x versions of Visual Studio 2017 contain a bug that
prevent them from compiling the following construct under certain
conditions:

std::unique_ptr<std::unique_ptr<Foo> []> foos;

This will fail to compile if Foo is an abstract class. To work-around
the problem the whole construct was change into:

std::vector<std::unique_ptr<Foo>> foos;

This not only fixes the compiler error but is also more readable than
previous version.

2 files changed, 2 insertions, 3 deletions

diff --git a/src/google/protobuf/compiler/cpp/cpp_field.cc b/src/google/protobuf/compiler/cpp/cpp_field.cc
index 33ffe574..0de20f84 100644
--- a/src/google/protobuf/compiler/cpp/cpp_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_field.cc
@@ -117,8 +117,7 @@ FieldGeneratorMap::FieldGeneratorMap(const Descriptor* descriptor,
                                      SCCAnalyzer* scc_analyzer)
     : descriptor_(descriptor),
       options_(options),
-      field_generators_(
-          new std::unique_ptr<FieldGenerator>[descriptor->field_count()]) {
+      field_generators_(descriptor->field_count()) {
   // Construct all the FieldGenerators.
   for (int i = 0; i < descriptor->field_count(); i++) {
     field_generators_[i].reset(
diff --git a/src/google/protobuf/compiler/cpp/cpp_field.h b/src/google/protobuf/compiler/cpp/cpp_field.h
index 6cb466a8..8cdbe886 100644
--- a/src/google/protobuf/compiler/cpp/cpp_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_field.h
@@ -203,7 +203,7 @@ class FieldGeneratorMap {
  private:
   const Descriptor* descriptor_;
   const Options& options_;
-  std::unique_ptr<std::unique_ptr<FieldGenerator> []> field_generators_;
+  std::vector<std::unique_ptr<FieldGenerator>> field_generators_;
 
   static FieldGenerator* MakeGenerator(const FieldDescriptor* field,
                                        const Options& options,