use-pkg-config

This project was generated by cmake-init.
It's heavily stripped down to focus on showing how to use a dependency that does not support clients using CMake.

The problem

You are developing a project, which has a dependency that does not support clients using CMake. You wish to use it regardless and also make it easy to transitively depend on.

For this example, gumbo-parser was chosen, because it has the perfect characteristics:

• It does not support clients using CMake, but does provide pkg-config .pc files
• vcpkg packages this library, but does not install the .pc files nor provide an unofficial CMake package (or at least until this issue is resolved)

This would be the same problem even if the dependency used CMake, but did not support clients using CMake. Failure to provide an install interface via a CMake package is one way to cause this.

The solution

When faced with a dependency that does not support clients using CMake is when developers are forced to write a find module. This repository has such a find module: Findgumbo.cmake

However, we do not want to be forced or to force people building this project to use that find module if we can help it. For this reason, project code does not directly make use of it and instead it is the responsibility of the person configuring this project to provide it if necessary.

Now we have to consider clients using vcpkg as well. When vcpkg packages something that does not officially support clients using CMake, they usually use an unofficial prefix for the package and target names (see libuv). This is done so vcpkg is forwards compatible if a package ever starts supporting clients who use CMake. Working around this requires quite a bit of elbow grease:

• The package and target names must be configurable
  • in the build interface
  • and the install interface
• The dependency's target name used for building must not leak into the install interface, so hide it

The defaults in the CMake code highlighted above all assume an optimistic outcome, e.g. the developer may use presets to simplify his workflow by setting the variables up as necessary, like it is done for the CI of this project. Package managers (the people) are given all the tools to work out the kinks by just setting a few variables and there won't be any need to patch anything in this project.

Conclusion

Provide a CMake package, even if you don't use CMake yourself, but if you are using CMake yourself and don't provide a CMake package, you are subjecting your clients to the above.