DOC: Add note on naming convention inconsistencies

[anishk85]

Pull Request: Clarify Naming Convention Deviations in ROS 2 C++ Style Guide

What was fixed?

• Added a clear notice in the C++ "Variable Naming" section of the documentation.
• The notice explains that ROS 2 projects use a mix of snake_case, PascalCase, and UPPER_CASE for constants and variables, which deviates from the Google C++ Style Guide (which recommends kPascalCase for constants).
• Rationale and guidance were provided for contributors:
  • This deviation is due to historical reasons and consistency with existing ROS codebases.
  • New projects should follow the conventions used in related ROS 2 packages.
  • When in doubt, contributors should prefer consistency with surrounding code over strict adherence to Google style.

Why was this needed?

• There was confusion among contributors about the naming conventions, since the documentation referenced the Google C++ Style Guide but did not explain the deviations.
• This update makes the documentation more transparent and helps maintain consistency across the codebase.

Where was it fixed?

• The change was made in
  source/The-ROS2-Project/Contributing/Code-Style-Language-Versions.rst
  under the C++ > Variable Naming section.

---

Example of the new notice:

Note on naming conventions:
ROS 2 deviates from the Google C++ Style Guide in several naming areas:

• The Google style guide recommends kPascalCase for constants (e.g., kDaysInAWeek)
• ROS 2 projects currently use a mix of snake_case, PascalCase, and UPPER_CASE naming conventions
• This deviation is for historical reasons and consistency with existing ROS codebases
• For new projects, developers should follow the existing conventions in related ROS 2 packages
• When in doubt, prefer consistency with surrounding code over strict adherence to Google style

---

This change improves clarity for all contributors and reviewers working on ROS 2 C++ code.

[fujitatomoya]

a few minor comments, basically lgtm but i would like to have another maintainer review before merge.

[anishk85]

@fujitatomoya okay so how does this looks to you

Note on naming conventions:

ROS 2 projects show inconsistent application of the Google C++ Style Guide for constants and naming:

• The Google style guide recommends kPascalCase for constants (e.g., kDaysInAWeek)

• Across ROS 2 packages, you'll find constants named using kPascalCase (e.g., in rosbag2_cpp),
  UPPER_CASE, PascalCase, and snake_case

• Guidance for contributors:

  • For new code, follow the existing conventions in your specific package to maintain local consistency
  • When starting new packages or when conventions are unclear, prefer kPascalCase as it aligns
    with the Google C++ Style Guide
  • Reserve UPPER_CASE for macros only
  • Use snake_case for variables and functions (avoid PascalCase in these contexts)
  • When in doubt, prioritize consistency with surrounding code over strict adherence to any single convention

[fujitatomoya]

@anishk85 thanks for the reply.

The Google style guide recommends kPascalCase for constants (e.g., kDaysInAWeek)

i would remove this, because it is just a recommendation in Google code style that has been said in the top of this section already. probably we do not re-explain the recommendation of Google code style.

other than that, i am okay with it. but i would like to have another review from maintainers before merge.

[anishk85]

@fujitatomoya can you tag another reviewer to kindly review this as soon as possible

[fujitatomoya]

@christophebedard @ahcorde can you take a look at this when you have time?