Add support for FetchContent

.github/workflows/cmake.yml

@@ -11,6 +11,7 @@ jobs:
  build_type: [Debug, Release]
  name: [gcc, clang, windows, clang-cfi]
  build_shared_libs: [ON, OFF]
+ fetch_content: [ON, OFF]
  include:
  - name: gcc
  ar: /usr/bin/ar
@@ -78,7 +79,7 @@ jobs:
  - name: cmake lib2
  run: |
  mkdir build_lib2
- cmake -S library2 -B build_lib2 -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/install_path" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 || exit 1
+ cmake -S library2 -B build_lib2 -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/install_path" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 -DBUILD_FETCH_CONTENT:BOOL="${{ matrix.fetch_content }}" || exit 1
  cmake --build build_lib2/ --target ${{ matrix.buildall }} --config ${{ matrix.build_type }} || exit 1
  cmake --build build_lib2/ --target install --config ${{ matrix.build_type }} || exit 1
  cd build_lib2 || exit 1
@@ -93,7 +94,7 @@ jobs:
  - name: cmake lib3
  run: |
  mkdir build_lib3
- cmake -S library3 -B build_lib3 -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/install_path" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 || exit 1
+ cmake -S library3 -B build_lib3 -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/install_path" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 -DBUILD_FETCH_CONTENT:BOOL="${{ matrix.fetch_content }}" || exit 1
  cmake --build build_lib3/ --target ${{ matrix.buildall }} --config ${{ matrix.build_type }} || exit 1
  cmake --build build_lib3/ --target install --config ${{ matrix.build_type }} || exit 1
  cd build_lib3 || exit 1
@@ -108,7 +109,7 @@ jobs:
  - name: cmake lib4
  run: |
  mkdir build_lib4
- cmake -S library4 -B build_lib4 -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -Dlibrary2_DIR="${{ github.workspace }}/install_path/lib/cmake/library2" -Dlibrary3_DIR="${{ github.workspace }}/install_path/lib/cmake/library3" -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/install_path" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 || exit 1
+ cmake -S library4 -B build_lib4 -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -Dlibrary2_DIR="${{ github.workspace }}/install_path/lib/cmake/library2" -Dlibrary3_DIR="${{ github.workspace }}/install_path/lib/cmake/library3" -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/install_path" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 -DBUILD_FETCH_CONTENT:BOOL="${{ matrix.fetch_content }}" || exit 1
  cmake --build build_lib4/ --target ${{ matrix.buildall }} --config ${{ matrix.build_type }} || exit 1
  cmake --build build_lib4/ --target install --config ${{ matrix.build_type }} || exit 1
  cd build_lib4 || exit 1
@@ -123,7 +124,7 @@ jobs:
  - name: cmake main
  run: |
  mkdir main
- cmake -S extern -B main -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -Dlibrary2_DIR="${{ github.workspace }}/install_path/lib/cmake/library2" -Dlibrary3_DIR="${{ github.workspace }}/install_path/lib/cmake/library3" -Dlibrary4_DIR="${{ github.workspace }}/install_path/lib/cmake/library4" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 || exit 1
+ cmake -S extern -B main -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -Dlibrary_DIR="${{ github.workspace }}/install_path/lib/cmake/library" -Dlibrary2_DIR="${{ github.workspace }}/install_path/lib/cmake/library2" -Dlibrary3_DIR="${{ github.workspace }}/install_path/lib/cmake/library3" -Dlibrary4_DIR="${{ github.workspace }}/install_path/lib/cmake/library4" -DCMAKE_CXX_COMPILER="${{ matrix.cxx }}" -DCMAKE_AR="${{ matrix.ar }}" -DCMAKE_RANLIB="${{ matrix.ranlib }}" -DBUILD_SHARED_LIBS:BOOL=${{ matrix.build_shared_libs }} -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}" -DCMAKE_EXE_LINKER_FLAGS="${{ matrix.ld_flags }}" -DCMAKE_CXX_STANDARD=20 -DBUILD_FETCH_CONTENT:BOOL="${{ matrix.fetch_content }}" || exit 1
  cmake --build main/ --target ${{ matrix.buildall }} --config ${{ matrix.build_type }} || exit 1
  - name: ctest main
  shell: bash

README.md

@@ -25,7 +25,7 @@ After, a simple executable `extern` is linked with `library4`.
 
 ## CMakeLists.txt
 
-All interesting data in this POC are in `CMakeLists.txt` files in `library` folder. The other folders are just a clone of this folder to show that everything is working well for the worst scenario.
+All interesting data in this POC are in `CMakeLists.txt` files in `library` folder. There is also comment about `BUILD_FETCH_CONTENT` in `lib/CmakeLists.txt` for `library2`. The other folders are just a clone of the main folder to show that everything is working well for the worst scenario.
 
 You need to know the basics of CMake. The whole [official tutorial](https://cmake.org/cmake/help/latest/guide/tutorial/index.html) is perfect.
 
@@ -43,6 +43,8 @@ Diamond dependency doesn't look to be a problem with this example.
 
 Don't explicitly (on user side) depends on `library` when linking `library2` or `library3`. But you need to explicitly do it in `Config.cmake` file.
 
+Libraries can be built with `FetchContent` or `find_package`. Simply set `BUILD_FETCH_CONTENT` option.
+
 ## Fix-me
 
-Don't set `CMAKE_INSTALL_RPATH` and `CMAKE_INSTALL_RPATH_USE_LINK_PATH` in `CMakeLists.txt`. But without it, CI don't pass.
+Don't set `CMAKE_INSTALL_RPATH` and `CMAKE_INSTALL_RPATH_USE_LINK_PATH` in `CMakeLists.txt`. But without it, CI doesn't pass.

extern/CMakeLists.txt

@@ -3,11 +3,25 @@ cmake_minimum_required(VERSION 3.21)
 project(Extern)
 
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
+option(BUILD_FETCH_CONTENT
+ "Use FetchContext instead of find_package for external library" OFF)
 
-find_package(library REQUIRED)
-find_package(library2 REQUIRED)
-find_package(library3 REQUIRED)
-find_package(library4 REQUIRED)
+if(BUILD_FETCH_CONTENT)
+ include(FetchContent)
+ set(BUILD_TESTING_SAVE ${BUILD_TESTING})
+ set(BUILD_TESTING OFF)
+ FetchContent_Declare(library4 SOURCE_DIR
+ "${CMAKE_CURRENT_SOURCE_DIR}/../library4")
+ FetchContent_GetProperties(library4)
+ if(NOT library4_POPULATED)
+ FetchContent_Populate(library4)
+ add_subdirectory(${library4_SOURCE_DIR} ${library4_BINARY_DIR}
+ EXCLUDE_FROM_ALL)
+ endif()
+ set(BUILD_TESTING ${BUILD_TESTING_SAVE})
+else()
+ find_package(library4 REQUIRED)
+endif()
 
 add_executable(test1 main1.cpp)
 target_link_libraries(test1 PRIVATE library::library)

library/lib/CMakeLists.txt

@@ -8,6 +8,10 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/include/${PROJECT_NAME}/version.h.in
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
 add_library(${PROJECT_NAME})
+# library will be installed in a namespace library. But if you don't install the
+# library (and use it with add_subdirectory / FetchContent), an alias for
+# library::library is needed.
+add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
 include(GenerateExportHeader)
 
@@ -46,12 +50,11 @@ target_sources(
 # only if you built library with BUILD_SHARED_LIBS and want to use installed
 # headers in STATIC library.
 
-# In shared mode, CMake automatically defines ${PROJECT_NAME}_Export in private.
+# For shared library, CMake automatically defines ${PROJECT_NAME}_Export in
+# private.
 
-#if(NOT BUILD_SHARED_LIBS)
-# target_compile_definitions(${PROJECT_NAME}
-# PUBLIC ${PROJECT_NAME}_STATIC_DEFINE)
-#endif()
+# target_compile_definitions(${PROJECT_NAME} PUBLIC
+# ${PROJECT_NAME}_STATIC_DEFINE)
 
 # BUILD_INTERFACE will be the include folder when you build the library.
 

library2/CMakeLists.txt

@@ -9,6 +9,8 @@ set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
 
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
+option(BUILD_FETCH_CONTENT
+ "Use FetchContext instead of find_package for external library" OFF)
 
 include(GNUInstallDirs)
 include(CMakePackageConfigHelpers)

library2/lib/CMakeLists.txt

@@ -5,6 +5,7 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/include/${PROJECT_NAME}/version.h.in
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
 add_library(${PROJECT_NAME})
+add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
 include(GenerateExportHeader)
 
@@ -19,7 +20,31 @@ set(${PROJECT_NAME}_HEADER_AUTO
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/subfolder/helper.h
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
-find_package(library REQUIRED)
+# Test compilation / build with FetchContent_Declare or find_package
+if(BUILD_FETCH_CONTENT)
+ include(FetchContent)
+ # There is a target test1 in library and library2. Hack to disable
+ # BUILD_TESTING only in library.
+ set(BUILD_TESTING_SAVE ${BUILD_TESTING})
+ set(BUILD_TESTING OFF)
+ FetchContent_Declare(library SOURCE_DIR
+ "${CMAKE_CURRENT_SOURCE_DIR}/../../library")
+ # Don't use FetchContent_MakeAvailable since it doesn't support
+ # EXCLUDE_FROM_ALL. If you don't EXCLUDE_FROM_ALL, you will install library
+ # with library2.
+ FetchContent_GetProperties(library)
+ if(NOT library_POPULATED)
+ FetchContent_Populate(library)
+ add_subdirectory(${library_SOURCE_DIR} ${library_BINARY_DIR}
+ EXCLUDE_FROM_ALL)
+ endif()
+ set(BUILD_TESTING ${BUILD_TESTING_SAVE})
+else()
+ find_package(library REQUIRED)
+endif()
+# With FetchContent, library::library is an alias to library.
+
+# With find_package, it's a real namespace::library.
 target_link_libraries(${PROJECT_NAME} PUBLIC library::library)
 
 target_sources(

library3/CMakeLists.txt

@@ -9,6 +9,8 @@ set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
 
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
+option(BUILD_FETCH_CONTENT
+ "Use FetchContext instead of find_package for external library" OFF)
 
 include(GNUInstallDirs)
 include(CMakePackageConfigHelpers)

library3/lib/CMakeLists.txt

@@ -5,6 +5,7 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/include/${PROJECT_NAME}/version.h.in
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
 add_library(${PROJECT_NAME})
+add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
 include(GenerateExportHeader)
 
@@ -19,7 +20,22 @@ set(${PROJECT_NAME}_HEADER_AUTO
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/subfolder/helper.h
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
-find_package(library REQUIRED)
+if(BUILD_FETCH_CONTENT)
+ include(FetchContent)
+ set(BUILD_TESTING_SAVE ${BUILD_TESTING})
+ set(BUILD_TESTING OFF)
+ FetchContent_Declare(library SOURCE_DIR
+ "${CMAKE_CURRENT_SOURCE_DIR}/../../library")
+ FetchContent_GetProperties(library)
+ if(NOT library_POPULATED)
+ FetchContent_Populate(library)
+ add_subdirectory(${library_SOURCE_DIR} ${library_BINARY_DIR}
+ EXCLUDE_FROM_ALL)
+ endif()
+ set(BUILD_TESTING ${BUILD_TESTING_SAVE})
+else()
+ find_package(library REQUIRED)
+endif()
 target_link_libraries(${PROJECT_NAME} PUBLIC library::library)
 
 target_sources(

library4/CMakeLists.txt

@@ -1,7 +1,5 @@
 cmake_minimum_required(VERSION 3.23)
 
-# Configuration of the project needs to set VERSION to generate .cmake files and
-# to use find_package.
 project(
  library4
  LANGUAGES CXX
@@ -10,26 +8,20 @@ project(
 set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
 
-# You need to explicitly set BUILD_SHARED_LIBS option to enable static / shared
-# library. But don't customize variable name.
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
+option(BUILD_FETCH_CONTENT
+ "Use FetchContext instead of find_package for external library" OFF)
 
-# Set default library path to install
 include(GNUInstallDirs)
-# Features to generate .cmake file for find_package.
 include(CMakePackageConfigHelpers)
 
-# Configuration of the library
 add_subdirectory(lib)
 
-# Enable tests.
 include(CTest)
-# BUILD_TESTING is defined via include(CTest)
 if(BUILD_TESTING)
  add_subdirectory(tests)
 endif()
 
-# Generate an installer (requires nsis)
 include(InstallRequiredSystemLibraries)
 include(CPack)
 set(CPACK_RESOURCE_FILE_LICENSE "${CMAKE_CURRENT_SOURCE_DIR}/../LICENSE")
@@ -38,12 +30,10 @@ set(CPACK_PACKAGE_VERSION_MINOR "${${PROJECT_NAME}_VERSION_MINOR}")
 set(CPACK_PACKAGE_VERSION_PATCH "${${PROJECT_NAME}_VERSION_PATCH}")
 set(CPACK_PACKAGE_VERSION_TWEAK "${${PROJECT_NAME}_VERSION_TWEAK}")
 set(CPACK_SOURCE_GENERATOR "TGZ")
-# It's better that the folder path have the version of the library.
 file(
  TO_NATIVE_PATH
  "${PROJECT_NAME}/${CPACK_PACKAGE_VERSION_MAJOR}.${CPACK_PACKAGE_VERSION_MINOR}.${CPACK_PACKAGE_VERSION_PATCH}"
  path_suggested)
-# Need to escape backslash for NSIS.
 string(REPLACE "\\" "\\\\" path_suggested "${path_suggested}")
 set(CPACK_PACKAGE_INSTALL_DIRECTORY "${path_suggested}")
 set(CPACK_NSIS_PACKAGE_NAME

library4/lib/CMakeLists.txt

@@ -5,6 +5,7 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/include/${PROJECT_NAME}/version.h.in
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
 add_library(${PROJECT_NAME})
+add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
 include(GenerateExportHeader)
 
@@ -19,8 +20,31 @@ set(${PROJECT_NAME}_HEADER_AUTO
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/subfolder/helper.h
  ${CMAKE_CURRENT_BINARY_DIR}/include/${PROJECT_NAME}/version.h)
 
-find_package(library2 REQUIRED)
-find_package(library3 REQUIRED)
+if(BUILD_FETCH_CONTENT)
+ include(FetchContent)
+ set(BUILD_TESTING_SAVE ${BUILD_TESTING})
+ set(BUILD_TESTING OFF)
+ FetchContent_Declare(library2 SOURCE_DIR
+ "${CMAKE_CURRENT_SOURCE_DIR}/../../library2")
+ FetchContent_GetProperties(library2)
+ if(NOT library2_POPULATED)
+ FetchContent_Populate(library2)
+ add_subdirectory(${library2_SOURCE_DIR} ${library2_BINARY_DIR}
+ EXCLUDE_FROM_ALL)
+ endif()
+ FetchContent_Declare(library3 SOURCE_DIR
+ "${CMAKE_CURRENT_SOURCE_DIR}/../../library3")
+ FetchContent_GetProperties(library3)
+ if(NOT library3_POPULATED)
+ FetchContent_Populate(library3)
+ add_subdirectory(${library3_SOURCE_DIR} ${library3_BINARY_DIR}
+ EXCLUDE_FROM_ALL)
+ endif()
+ set(BUILD_TESTING ${BUILD_TESTING_SAVE})
+else()
+ find_package(library2 REQUIRED)
+ find_package(library3 REQUIRED)
+endif()
 target_link_libraries(${PROJECT_NAME} PUBLIC library2::library2
  library3::library3)