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Keeping Your CMake Code Future-Proof with CMAKE_WARN_DEPRECATED


Purpose

  • By default, CMake enables these warnings (CMAKE_WARN_DEPRECATED=TRUE), helping you identify code that might need to be updated to stay compatible with future CMake versions.
  • In CMake, the CMAKE_WARN_DEPRECATED variable controls whether the build system issues warnings when encountering deprecated features or functionality.

How it Works

  • You can check for these warnings in your build output, typically in the terminal or command prompt window where you execute CMake.
  • These warnings serve as a heads-up that the code might require adjustments to work seamlessly with future CMake releases.
  • When set to TRUE (the default), CMake generates warnings during the build process whenever it encounters usage of deprecated variables, commands, or other features.

Setting CMAKE_WARN_DEPRECATED

  • While it's generally recommended to keep the default setting (TRUE), you can explicitly control the behavior using the set command in your CMakeLists.txt file:

    set(CMAKE_WARN_DEPRECATED FALSE)  # Disable warnings

    Important
    Disabling warnings might mask potential issues that could arise in the future. Consider this option only if you have a specific reason to suppress them temporarily.

Benefits of Using Warnings

  • This allows you to proactively address these issues and ensure your code remains functional as CMake evolves.
  • By enabling CMAKE_WARN_DEPRECATED, you gain valuable insights into potential compatibility issues with newer CMake versions.

In Summary

  • While disabling warnings might seem convenient in specific cases, it's generally best practice to use the default setting (enabled) to safeguard your code's long-term functionality.
  • By keeping it enabled, you receive warnings about deprecated features, allowing you to update your code accordingly.
  • The CMAKE_WARN_DEPRECATED variable is a valuable tool for maintaining code compatibility with future CMake versions.

Scenario 1: Enabled Warnings (Default)

# CMakeLists.txt

# This is a deprecated command (use find_package instead)
find_library(MY_LIBRARY NAMES mylib PATHS /path/to/mylib)

# Build the target
add_executable(my_program main.cpp)
target_link_libraries(my_program MY_LIBRARY)

When you run CMake with this configuration and CMAKE_WARN_DEPRECATED is enabled (default), you'll likely see a warning similar to:

CMake Warning at /path/to/project/CMakeLists.txt:3:
  The command 'find_library' is deprecated. Use 'find_package' instead.
Call Stack (most recent call first):
  CMakeLists.txt:3

This warning indicates that find_library is no longer recommended, and you should use find_package for better package management.

Scenario 2: Disabled Warnings

# CMakeLists.txt (same except for disabling warnings)

set(CMAKE_WARN_DEPRECATED FALSE)  # Disable deprecation warnings

# (Rest of the code remains the same)

If you explicitly disable warnings with set(CMAKE_WARN_DEPRECATED FALSE), you won't see the deprecation warning about find_library. However, this doesn't mean the issue goes away. It might cause problems in future CMake versions.

  • Disabling warnings should be a last resort, and only for temporary purposes while updating code to address the deprecation issue.
  • Consider using linters or code analysis tools that can detect deprecated features alongside CMake warnings.
  • Use clear and concise variable names and comments to maintain code readability even when warnings are disabled.

  1. Using Modern CMake Practices

    The best way to avoid relying on CMAKE_WARN_DEPRECATED is to write CMake code that adheres to current best practices. This includes using recommended commands like find_package instead of deprecated ones like find_library. CMake documentation and online resources often highlight deprecated features and suggest alternatives.

  2. Compiler Warnings

    While CMAKE_WARN_DEPRECATED focuses on CMake-specific deprecations, your compilers can also generate warnings about deprecated compiler features or library usage. Familiarize yourself with your compiler's warning flags (e.g., -Wdeprecated for GCC/Clang) and enable them to catch potential issues during the build process.

  3. Static Code Analysis Tools

    Consider using static code analysis tools like Clang-Tidy or PVS-Studio that can identify deprecated code constructs, along with other potential coding issues, within your CMake project. These tools can provide a more comprehensive analysis beyond just CMake-specific warnings.

  4. Manually Checking Documentation

    If you're unsure whether a specific CMake feature is deprecated, consult the official CMake documentation for the version you're using. The documentation often mentions deprecations and highlights the recommended alternatives.