Add CMake Config-file package

[kevinAlbs]

Summary

This PR resolves #250 by creating CMake Config-file Package.

Motivation

https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html#config-file-packages notes:

Config-file packages are provided by upstream vendors as part of development packages, that is, they belong with the header files and any other files provided to assist downstreams in using the package

Including a CMake Config-file Package enables CMake consumers to use find_package to find and use utf8proc:

add_executable (app app.c)
find_package (utf8proc 2.9.0 REQUIRED)
target_link_libraries (app PRIVATE utf8proc::utf8proc)

The absence of a CMake Config-file Package may add difficulty using utf8proc in a CMake project. For example: the MongoDB C driver includes FindUtf8Proc.cmake using pkg-config. However, using pkg-config is not suitable for consumers building with MSVC (the -l and -L flags are unrecognized).

Use of relative paths in 422de38 is intended to make the installed package relocatable.

[kevinAlbs]

Thank you for the review @kou. Feedback has been applied.

[kou]

+1

(But I'm not a maintainer of this project. I just an user of this project.)

[kevinAlbs]

@stevengj may I request merging this PR? This may help using utf8proc with CMake.

[kou]

@stevengj @eschnett Could you take a look at this?

[eschnett]

This is a nice modernization of the cmake file. However, I see that these changes are not tested in CI. Did you test them? Do you have a package that uses utf8proc via cmake, using the mechanisms you describe?

If a package is undergoing regular development, then changes to the build system are automatically tested. utf8proc is currently in a rather quiet stage, and as such, all changes need to be well tested – otherwise an error might creep in, and people would only notice a year from now when the next feature change is made, and downstream package are trying to use cmake to build utf8proc.

I know that it is very uncommon to have CI test the packaging mechanism. I argue it should in general, but I'm not going to insist since this would be a lot of work. I still would like you to confirm that you tested all the features you're introducing. (Kudos for updating the documentation explaining how to use cmake in a modern way.)

[kou]

We can add a CI job for the CMake package by just creating a small CMake project something like:

/* app.c */
#include <stdio.h>
#include <utf8proc.h>

int
main(void)
{
  printf("%s\n", utf8proc_version());
  return 0;
}

# CMakeLists.txt
cmake_minimum_required(VERSION 3.16)
project(utf8proc-test)
find_package(utf8proc REQUIRED)
add_executable(app app.c)
target_link_libraries(app utf8proc::utf8proc)

$ cmake -S . -B build -DCMAKE_PREFIX_PATH=${UTF8PROC_PREFIX}
$ make -C build

@kevinAlbs Can you add a CI job for this CMake package? (Or I can work work on it.)

FYI: I'm using utf8proc in https://github.com/apache/arrow . But we use our Findutf8proc.cmake https://github.com/apache/arrow/blob/main/cpp/cmake_modules/Findutf8proc.cmake not this CMake package for now.

[kevinAlbs]

@kevinAlbs Can you add a CI job for this CMake package?

Done. 8ed21d9 adds a test to GitHub actions for consuming the package with CMake. Thank you for the starter code.

[kou]

How about adding -DCMAKE_INSTALL_PREFIX=tmp/install to cmake -S . ... in the name: Build step instead of using --prefix tmp/install here?

[kou]

I'm not sure we need this.

@eschnett Do you want to add this? If we want to use cmake -S test/app -B test/app/build ... for local development, this will be helpful. If we want to use cmake -S test/app -B ../test-app-build ... or something for local development, this is needless.

FYI: Our README has cmake -S . -B build but we don't have /build/ in this list.
https://github.com/JuliaStrings/utf8proc?tab=readme-ov-file#quick-start

[eschnett]

I would not add this. I would only add directories or files that are generated by the build system. The path where cmake builds is under user control and I frequently use different paths than those suggested in a packages's documentation. I have, however, no strong opinion on this.

[kevinAlbs]

Removed with 60205e4.

[kou]

+1

[kou]

@stevengj @eschnett Could you approve CI jobs and review this? If there is no more concerns, could you merge this?