std::make_shared calls are now [[nodiscard]] in MSVC and cause build warnings

[brawner]

Bug report

Required Info:

• Operating System:
  • Windows 10
• Installation type:
  • Source install, MSVC 2019, 16,24
• Version or commit hash:
  • master

Issue

std::make_shared is now annotated as [[nodiscard]] on Windows MSVC 2019 and will cause MSBuild warnings. I can't tell if that's part of the STL spec, or if this is something that MS has decided to do.

This was noticed on the citest farm instance I'm running in a docker container. It installs the most recent VS BuildTools which may be ahead of the ci.ros2.org version.

This affects test_node.cpp and test_parameter_client.cpp
https://github.com/ros2/rclcpp/blob/master/rclcpp/test/test_node.cpp
https://github.com/ros2/rclcpp/blob/master/rclcpp/test/test_parameter_client.cpp

If desired, I can create a corresponding PR. Wrapping the make shared call in an EXPECT_TRUE(make_shared() != nullptr) statement would probably resolve the issue.

[dirk-thomas]

A pull request would be appreciated. I would suggest to simply assign the returned value to a local variable.

[Karsten1987]

FWIW, you might have to (void) that local variable then in order to avoid compiler warnings -Wunused.

[brawner]

@dirk-thomas PR opened for this issue

[wjwwood]

Closing as #963 was merged.