Latest Cmake (4.0) Causes Policy Issue In `CMakeLists.txt`

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Introduction

CMake is a powerful build system that is widely used in the software development industry. It provides a flexible and platform-independent way to build and manage complex projects. However, with the latest version of CMake (4.0), a policy issue has been introduced that can cause problems for users who are not familiar with the changes. In this article, we will discuss the issue and provide a solution to fix it.

What is CMake Policy?

CMake policy is a set of rules that govern how CMake behaves in certain situations. These policies are used to ensure that CMake builds are consistent and predictable. CMake policies are defined using the cmake_policy command, which is used to set the policy for a specific version of CMake.

The Issue with CMake 4.0

The latest version of CMake (4.0) has deprecated the cmake_policy command. This means that users who are using the cmake_policy command in their CMakeLists.txt file will encounter an error when building their project with CMake 4.0. The error message will indicate that the cmake_policy command is no longer supported.

Example of the Issue

To illustrate the issue, let's take a look at an example CMakeLists.txt file from the ever-training repository:

cmake_minimum_required(VERSION 3.10)
project(ever-training)

# ... (other code)

cmake_policy(VERSION 3.10)
cmake_policy(SET CMP0054 NEW)

In this example, the cmake_policy command is used to set the policy for CMake version 3.10. However, when building the project with CMake 4.0, the cmake_policy command will cause an error.

Fixing the Issue

To fix the issue, users need to update their CMakeLists.txt file to use the new cmake_policy command. The new command is called cmake_policy_set, and it is used to set the policy for a specific version of CMake.

Here is an updated version of the CMakeLists.txt file:

cmake_minimum_required(VERSION 3.10)
project(ever-training)

# ... (other code)

cmake_policy_set(CMP0054 NEW)

In this updated version, the cmake_policy command has been replaced with the cmake_policy_set command.

Best Practices for Using CMake Policy

To avoid issues with CMake policy, users should follow these best practices:

  • Use the latest version of CMake.
  • Avoid using deprecated commands, such as cmake_policy.
  • Use the cmake_policy_set command to set the policy for a specific version of CMake.
  • Keep the CMakeLists.txt file up-to-date with the latest CMake features.

Conclusion

In conclusion, the latest version of CMake (4.0) has introduced a policy issue that can cause problems for users who are not familiar with the changes. However, by following the best practices outlined in this article, users can easily fix the issue and to use CMake to build their projects.

Common CMake Policy Issues

Here are some common CMake policy issues that users may encounter:

  • CMP0054: This policy issue is related to the use of the cmake_policy command. To fix the issue, users need to update their CMakeLists.txt file to use the cmake_policy_set command.
  • CMP0067: This policy issue is related to the use of the cmake_policy command with a version number. To fix the issue, users need to update their CMakeLists.txt file to use the cmake_policy_set command without a version number.
  • CMP0074: This policy issue is related to the use of the cmake_policy command with a policy name. To fix the issue, users need to update their CMakeLists.txt file to use the cmake_policy_set command with a policy name.

Troubleshooting CMake Policy Issues

If users encounter a CMake policy issue, they can try the following troubleshooting steps:

  • Check the CMake version: Make sure that the CMake version is up-to-date.
  • Check the CMakeLists.txt file: Make sure that the CMakeLists.txt file is up-to-date with the latest CMake features.
  • Check the policy settings: Make sure that the policy settings are correct.
  • Check the error message: Make sure that the error message is clear and provides useful information.

Conclusion

Q: What is CMake policy?

A: CMake policy is a set of rules that govern how CMake behaves in certain situations. These policies are used to ensure that CMake builds are consistent and predictable.

Q: Why is CMake policy important?

A: CMake policy is important because it helps to ensure that CMake builds are consistent and predictable. By following the CMake policy, users can avoid issues and ensure that their builds are successful.

Q: What is the difference between cmake_policy and cmake_policy_set?

A: The cmake_policy command is deprecated in CMake 4.0 and later. The cmake_policy_set command is used to set the policy for a specific version of CMake.

Q: How do I fix the CMP0054 policy issue?

A: To fix the CMP0054 policy issue, you need to update your CMakeLists.txt file to use the cmake_policy_set command instead of the cmake_policy command.

Q: What is the CMP0067 policy issue?

A: The CMP0067 policy issue is related to the use of the cmake_policy command with a version number. To fix the issue, you need to update your CMakeLists.txt file to use the cmake_policy_set command without a version number.

Q: What is the CMP0074 policy issue?

A: The CMP0074 policy issue is related to the use of the cmake_policy command with a policy name. To fix the issue, you need to update your CMakeLists.txt file to use the cmake_policy_set command with a policy name.

Q: How do I troubleshoot CMake policy issues?

A: To troubleshoot CMake policy issues, you can try the following steps:

  • Check the CMake version: Make sure that the CMake version is up-to-date.
  • Check the CMakeLists.txt file: Make sure that the CMakeLists.txt file is up-to-date with the latest CMake features.
  • Check the policy settings: Make sure that the policy settings are correct.
  • Check the error message: Make sure that the error message is clear and provides useful information.

Q: Can I use both cmake_policy and cmake_policy_set in the same CMakeLists.txt file?

A: No, you cannot use both cmake_policy and cmake_policy_set in the same CMakeLists.txt file. The cmake_policy command is deprecated in CMake 4.0 and later, and the cmake_policy_set command is used to set the policy for a specific version of CMake.

Q: How do I know which CMake policy to use?

A: To determine which CMake policy to use, you can check the CMake documentation or the CMake policy documentation. You can also use the cmake_policy command to list the available policies and their settings.

Q: Can I disable CMake policy checks?

A:, you can disable CMake policy checks by using the cmake_policy command with the CMP0054 policy name and setting it to OLD. However, this is not recommended, as it can lead to inconsistent and unpredictable builds.

Q: How do I report CMake policy issues?

A: To report CMake policy issues, you can submit a bug report to the CMake project or post a question on the CMake mailing list. Be sure to provide detailed information about the issue, including the CMake version, the CMakeLists.txt file, and the error message.