feat: Switch to c++20 and remove resulting compile warnings

[jmachowinski]

Description

Switch to cpp20 from lyrical onwards

Is this user-facing behavior change?

yes

Did you use Generative AI?

no

[jmachowinski]

Pulls: ros2/ament_cmake_ros#62, ros2/rcutils#548, #3124
Gist: https://gist.githubusercontent.com/jmachowinski/1538e0f1074c2a0133830f9b6e76ee32/raw/31a05eaaf436bc349c5bf99faec772cce9b5f581/ros2.repos
BUILD args:
TEST args:
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/18900

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[fujitatomoya]

lgtm with green CI

[ahcorde]

Pulls: #3124, ros2/ament_cmake_ros#62, ros2/rcutils#548
Gist: https://gist.githubusercontent.com/ahcorde/308c095a49dc34449d63c4dc7eac9439/raw/31a05eaaf436bc349c5bf99faec772cce9b5f581/ros2.repos
BUILD args: --packages-above-and-dependencies rclcpp ament_cmake_ros_core rmw_test_fixture_implementation rcutils
TEST args: --packages-above rclcpp ament_cmake_ros_core rmw_test_fixture_implementation rcutils
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/18943

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[claraberendsen]

Rebuilding here with the MSVC2022 flag turned on:

Note: This is a rebuild of an older build, not latest.

[claraberendsen]

Mhm... Looking at the log even with the parameter to 2022 it's not picking up MSVC2022. This seems like a bug on ci.ros2. I'll fix it and re-run.

[knmcguire]

Are you sure? Logs say that it opens up this dev environment:

*********************************************************************
** Visual Studio 2022 Developer Command Prompt v17.14.29
** Copyright (c) 2025 Microsoft Corporation
**********************************************************************

[claraberendsen]

You are correct, sorry for the noise. It's setting to MSVC2022 I saw

14:41:34 -- The C compiler identification is MSVC 19.44.35225.0

on the zenoh output and got confused with Windows version numbers.

19.44 is MSVC 2022.

[claraberendsen]

Ah I took the wrong point in time and rebuilt not the latest run. Here is the rebuild from run made by Alejandro

[skyegalaxy]

per client library WG meeting today: we'll run CI one more time and if linux is green, we'll merge this, ros2/ament_cmake_ros#62 and ros2/rcutils#548

[skyegalaxy]

Pulls: #3124, ros2/ament_cmake_ros#62, ros2/rcutils#548
Gist: https://gist.githubusercontent.com/skyegalaxy/c1125cbe48fe911d3211fef54246d06d/raw/a2987278e6f5a5125f605d68dd0f3d7ff6a82dd6/ros2%2520repos%2520c++20
BUILD args: --packages-above-and-dependencies rclcpp ament_cmake_ros_core rmw_test_fixture_implementation rcutils
TEST args: --packages-above rclcpp ament_cmake_ros_core rmw_test_fixture_implementation rcutils
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/18991/

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[mini-1235]

I am seeing:

/usr/bin/rosdep:6: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
  from pkg_resources import load_entry_point
ERROR: the following packages/stacks could not have their rosdep keys resolved
to system dependencies:
rclcpp: Cannot locate rosdep definition for [ament_index_cpp_core]

after this PR, I think this should be ament_cmake_ros_core right?

I created a PR here: #3133