Bazel is a build system that allows you to build software projects quickly and reliably. One of the features of Bazel is the ability to manage dependencies using Bzlmod files. Bzlmod files are used to describe the dependencies of a project and to ensure that the dependencies are compatible with each other.

The max_compatibility_level attribute in Bzlmod is used to specify the maximum compatibility level that a module dependency can have. This helps to ensure that the module dependency is compatible with the version of Bazel that is being used to build the project.

The compatibility level of a module is determined by the version of the Bzlmod file that it was created with. The higher the compatibility level, the more recent the version of Bzlmod that was used to create the module.

The default value of the max_compatibility_level attribute is 2. This means that the module dependency can be any version that is compatible with Bazel 2.0.0 or later.

If you specify a higher value for the max_compatibility_level, then the module dependency must be compatible with that version of Bazel or later. For example, if you specify 3, then the module dependency must be compatible with Bazel 3.0. 0 or later.

The max_compatibility_level attribute can be used to prevent compatibility errors when building a project. For example, if you are using Bazel 2.0.0 and you specify a max_compatibility_level of 3, then any module dependencies that are not compatible with Bazel 3.0.0 or later will cause an error.

Here is an example of how to use the max_compatibility_level attribute:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "my_module",
    url = "https://example.com/my_module.bzlmod",
    max_compatibility_level = 3,
)

In this example, the my_module module dependency must be compatible with Bazel 3.0.0 or later.

Here are some of the benefits of using the max_compatibility_level attribute:

• It can help to prevent compatibility errors when building a project.
• It can help to ensure that the project is compatible with future versions of Bazel.
• It can help to make the project more portable.

Here are some of the drawbacks of using the max_compatibility_level attribute:

• It can prevent the project from using older versions of modules that are still compatible with Bazel.
• It can make the project more difficult to maintain, as you need to keep track of the compatibility levels of all of the modules that the project depends on.

Overall, the max_compatibility_level attribute is a powerful tool that can be used to ensure the compatibility of a project with Bazel. However, it is important to weigh the benefits and drawbacks of using the attribute before deciding whether or not to use it.