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diff --git a/doc/being-consumed-by-cmake.md b/doc/being-consumed-by-cmake.md new file mode 100644 index 0000000..14ec93b --- /dev/null +++ b/doc/being-consumed-by-cmake.md @@ -0,0 +1,167 @@ +Being consumed by CMake +======================= + +To support libraries built with JustBuild to be consumed by CMake, the +rule `["CC", "install-with-deps"]` can be used. This rule will install +the library's artifacts, its public headers, and a pkg-config file, +which can be used by CMake to properly consume the library. + +In this example, we show how to build and install the `ssl` library with +JustBuild, so it can be picked up and used by CMake afterwards. + +Example: Build and install the `ssl` Library with JustBuild +----------------------------------------------------------- + +First make sure that `just`, `just-mr`, and `just-import-git` are +available in your `PATH`. Then, define a new workspace by creating the +`ROOT` marker. + +``` sh +$ touch ROOT +``` + +The `ssl` library that we want to use is a defined dependency of the +JustBuild repository `just/ssl`. To define a repository for that +library, create the following `repos.template.json` file. + +``` {.jsonc srcname="repos.template.json"} +{ "main": "ssl" +, "repositories": + { "ssl": + { "repository": {"type": "file", "path": "."} + , "bindings": {"rules": "rules-cc", "just-ssl": "just/ssl"} + } + } +} +``` + +and import the `rules-cc` and JustBuild repository, including its +dependency `just/ssl`, via: + +``` sh +$ cat repos.template.json \ + | just-import-git -C - --as just -b master https://github.com/just-buildsystem/justbuild \ + | just-import-git -C - --as rules-cc -b master https://github.com/just-buildsystem/rules-cc \ + > repos.json +$ +``` + +Next, the following `TARGETS` file needs to be provided. + +``` {.jsonc srcname="TARGETS"} +{ "ssl-lib": + { "type": ["@", "rules", "CC", "library"] + , "name": ["ssl"] + , "deps": [["@", "just-ssl", "", "ssl"]] + } +, "ssl-pkg": + {"type": ["@", "rules", "CC", "install-with-deps"], "targets": ["ssl-lib"]} +} +``` + +The library target `ssl-lib` specifies the name `"ssl"` (also used as +package name) and a dependency on the `ssl` library from `just-ssl`. +Note that although this library target is merely a "wrapper" +(header-only library without headers), it could equally well be a +full-blown library target. Furthermore, the package target `ssl-pkg` +installs the `ssl-lib` target including its dependencies and generates a +pkg-config file that can be later used by CMake. + +Finally, the `ssl-pkg` target can be built and installed to a specific +`PREFIX` (note that `OS` and `ARCH` must be set as well). + +``` sh +$ export PREFIX=/tmp/just_ssl +$ just-mr install -D'{"OS":"linux", "ARCH":"x64_64", "PREFIX":"'$PREFIX'"}' -o $PREFIX ssl-pkg +INFO: Requested target is [["@","ssl","","ssl-pkg"],{"ARCH":"x64_64","OS":"linux","PREFIX":"/tmp/just_ssl"}] +INFO: Analysed target [["@","ssl","","ssl-pkg"],{"ARCH":"x64_64","OS":"linux","PREFIX":"/tmp/just_ssl"}] +INFO: Export targets found: 0 cached, 2 uncached, 0 not eligible for caching +INFO: Discovered 269 actions, 3 trees, 1 blobs +INFO: Building [["@","ssl","","ssl-pkg"],{"ARCH":"x64_64","OS":"linux","PREFIX":"/tmp/just_ssl"}]. +PROG: [ 79%] 0 cached, 215 run, 8 processing (["@","just/ssl","","crypto-lib"]#105, ...). +INFO: Processed 269 actions, 0 cache hits. +INFO: Artifacts can be found in: + /tmp/just_ssl/include/openssl/aead.h [6d78db27d24746b39eacc20374697476e080c9f6:21054:f] + ... + /tmp/just_ssl/lib/libcrypto.a [df64da43f0168a717d09d609bf0c631d29c86b61:2336092:f] + /tmp/just_ssl/lib/libssl.a [77d2c2bfbe3ef3608895c854f1d1f6e1c200efd0:852620:f] + /tmp/just_ssl/share/pkgconfig/ssl.pc [9b69c758430f5b5fb6ff7a9b1f1ffc89471509af:406:f] +$ +``` + +Example: Consume the installed `ssl` Library with CMake +------------------------------------------------------- + +As an example, a minimal `main.c` file is created that depends on the +`ssl` library. + +``` {.c srcname="main.c"} +#include <openssl/evp.h> + +int main(int argc, char** argv) { + OpenSSL_add_all_algorithms(); + return 0; +} +``` + +In the `CMakeLists.txt` file, the `pkg_check_modules()` macro can be +used to determine the compile and linker flags needed to consume our +`ssl` library with CMake. + +``` {.cmake srcname="CMakeLists.txt"} +cmake_minimum_required(VERSION 3.1) + +project(test_ssl) + +find_package(PkgConfig REQUIRED) +pkg_check_modules(SSL REQUIRED ssl) + +add_executable(main main.c) +target_include_directories(main PRIVATE ${SSL_INCLUDE_DIRS}) +target_compile_options(main PRIVATE ${SSL_CFLAGS_OTHER}) +target_link_directories(main PRIVATE ${SSL_LIBRARY_DIRS}) +target_link_libraries(main PRIVATE ${SSL_LDFLAGS_OTHER} ${SSL_LIBRARIES}) +``` + +Note that `${SSL_LDFLAGS_OTHER}` can be omitted if the `ssl-pkg` target +was defined with a non-empty value for the field `"flat-libs"` (see rule +documentation of `["CC", "install-with-deps"]`). + +Finally, when running CMake, make sure to set the `CMAKE_PREFIX_PATH` to +the previously used install prefix in order to successfully find the +installed `ssl` library and its pkg-config file. + +``` sh +$ cmake -DCMAKE_PREFIX_PATH=/tmp/just_ssl -S . -B /tmp/test_ssl +-- The C compiler identification is GNU 10.2.1 +-- The CXX compiler identification is GNU 10.2.1 +-- Detecting C compiler ABI info +-- Detecting C compiler ABI info - done +-- Check for working C compiler: /usr/bin/cc - skipped +-- Detecting C compile features +-- Detecting C compile features - done +-- Detecting CXX compiler ABI info +-- Detecting CXX compiler ABI info - done +-- Check for working CXX compiler: /usr/bin/c++ - skipped +-- Detecting CXX compile features +-- Detecting CXX compile features - done +-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.2") +-- Checking for module 'ssl' +-- Found ssl, version unknown +-- Configuring done +-- Generating done +-- Build files have been written to: /tmp/test_ssl +$ cmake --build /tmp/test_ssl +[ 50%] Building CXX object CMakeFiles/main.dir/main.c.o +[100%] Linking CXX executable main +[100%] Built target main +$ +``` + +Note that if the package is moved to a different location, the `prefix` +variable within the pkg-config file `share/pkgconfig/ssl.pc` must be +updated as well. Alternatively, CMake can be instructed to automatically +guess the correct prefix by setting the variable `PKG_CONFIG_ARGN` to +`"--define-prefix"` (either on the command line or in the +`CMakeLists.txt`). However, this is a fairly recent CMake feature and +requires at least CMake version 3.22. |