build: Honor CMake USE_STD_FORMAT option (#761)

* Honor use_std_format option

Signed-off-by: Uilian Ries <[email protected]>

* use format option in contribution guide

Signed-off-by: Uilian Ries <[email protected]>

* Revert CMakePresets

Signed-off-by: Uilian Ries <[email protected]>

* Avoid cmake expression-generator

Signed-off-by: Uilian Ries <[email protected]>

* Add status message when not fiding std format

Signed-off-by: Uilian Ries <[email protected]>

---------

Signed-off-by: Uilian Ries <[email protected]>

CMakeLists.txt

@@ -4,16 +4,23 @@ project(faker-cxx LANGUAGES CXX)
 include(cmake/CompilerWarnings.cmake)
 
 option(USE_SYSTEM_DEPENDENCIES "Use fmt and GTest from system" OFF)
-option(USE_STD_FORMAT "Use std::format when available" ON)
 option(BUILD_EXAMPLES "Build examples" OFF)
 option(BUILD_TESTING "Build tests" ON)
 
-if (USE_STD_FORMAT)
+if (MSVC)
+    set(CMAKE_REQUIRED_FLAGS /std:c++20)
+else()
     set(CMAKE_REQUIRED_FLAGS -std=c++20)
-    include(CheckCXXSourceCompiles)
-    check_cxx_source_compiles("#include <format>\nint main(){ auto var = std::format(\"{}\", \"Hello\"); return 0; }"
-        HAS_STD_FORMAT)
-endif ()
+endif()
+include(CheckCXXSourceCompiles)
+check_cxx_source_compiles("#include <format>\nint main(){ auto var = std::format(\"{}\", \"Hello\"); return 0; }"
+    HAS_STD_FORMAT)
+if (NOT HAS_STD_FORMAT)
+    message(STATUS "Compiler has no support for std::format. Need to use fmt library as dependency.")
+endif()
+
+include(CMakeDependentOption)
+cmake_dependent_option(USE_STD_FORMAT "Use std::format when available" ON "HAS_STD_FORMAT" OFF)
 
 if (BUILD_TESTING)
     enable_testing()
@@ -119,8 +126,8 @@ install(EXPORT ${CMAKE_PROJECT_NAME}-targets
     FILE ${CMAKE_PROJECT_NAME}-config.cmake
     DESTINATION lib/cmake/${CMAKE_PROJECT_NAME})
 
-if (HAS_STD_FORMAT)
-    target_compile_definitions(${CMAKE_PROJECT_NAME} PRIVATE HAS_STD_FORMAT)
+if (USE_STD_FORMAT)
+    target_compile_definitions(${CMAKE_PROJECT_NAME} PRIVATE USE_STD_FORMAT)
 elseif (USE_SYSTEM_DEPENDENCIES)
     find_package(fmt CONFIG REQUIRED)
     target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE fmt::fmt)

CONTRIBUTING.md

@@ -140,6 +140,31 @@ Follow the steps below to build the project:
     cmake --build --preset unixlike-gcc-debug-static
     ```
 
+#### Choosing between STL std::format and fmt library
+
+The faker-cxx project uses formated string feature, which can be solved by:
+
+- [fmt](https://github.com/fmtlib/fmt) library
+- [std::format](https://en.cppreference.com/w/cpp/utility/format/format)
+
+The `std::format` requires C++20 standard support from the compiler. The feature is checked via CMake when building the project.
+In case available, the option `USE_STD_FORMAT` will be available:
+
+    ```sh
+    cmake -S . --preset unixlike-gcc-debug-static -DUSE_STD_FORMAT=ON
+    ```
+
+In case `std::format` is not available, faker-cxx will use `fmt` library instead. It can be used as external dependency via
+git submodules, or consumed from your system (installed by Conan or system package manager). In order to manage the way to
+acquire `fmt`, the CMake option `USE_SYSTEM_DEPENDENCIES` manages if should be used from system, or from git submodule:
+
+    ```sh
+    cmake -S . --preset unixlike-gcc-debug-static -DUSE_SYSTEM_DEPENDENCIES=OFF // Install from submodule
+    ```
+
+In case passing `USE_STD_FORMAT=ON` and `std::format` is not available, CMake will try to use `fmt` library automatically.
+Then, in case not finding `fmt`, it will fail.
+
 ### Testing the Project
 
 After building the project, you can run the tests to ensure everything is working correctly. We use CTest for running

src/common/FormatHelper.h

@@ -8,7 +8,7 @@
 #include "faker-cxx/types/Precision.h"
 #include "faker-cxx/Export.h"
 
-#if !defined(HAS_STD_FORMAT)
+#if !defined(USE_STD_FORMAT)
 #include <fmt/chrono.h>
 #include <fmt/core.h>
 #else
@@ -21,7 +21,7 @@ namespace faker
 class FormatHelper
 {
 public:
-#if !defined(HAS_STD_FORMAT)
+#if !defined(USE_STD_FORMAT)
     template <typename... Args>
     static std::string format(fmt::format_string<Args...> fmt, Args&&... args)
     {

tests/CMakeLists.txt

@@ -70,9 +70,9 @@ else ()
     target_link_libraries(${PROJECT_NAME} PRIVATE gtest_main gmock_main faker-cxx)
 endif ()
 
-if (HAS_STD_FORMAT)
+if (USE_STD_FORMAT)
     target_include_directories(${PROJECT_NAME} PRIVATE ${GTEST_INCLUDE_DIR} ${GMOCK_INCLUDE_DIR} ${CMAKE_CURRENT_LIST_DIR})
-    target_compile_definitions(${PROJECT_NAME} PRIVATE HAS_STD_FORMAT)
+    target_compile_definitions(${PROJECT_NAME} PRIVATE USE_STD_FORMAT)
 else ()
     target_link_libraries(${PROJECT_NAME} PRIVATE $<IF:$<TARGET_EXISTS:fmt::fmt>,fmt::fmt,fmt>)
     target_include_directories(${PROJECT_NAME} PRIVATE ${FMT_INCLUDE_DIR} ${GTEST_INCLUDE_DIR} ${GMOCK_INCLUDE_DIR} ${CMAKE_CURRENT_LIST_DIR})