write_compiler_detection_header¶

CMake documentation

WriteCompilerDetectionHeader

This module doesn’t provide enough abstraction. You have to specify supported compilers explicitly. From documentation:

Compilers which are known to CMake, but not specified are detected and a
preprocessor #error is generated for them.

Meaning that this code:

# CMakeLists.txt

cmake_minimum_required(VERSION 3.10)
project(foo)

include(WriteCompilerDetectionHeader)

set(gen_include "${CMAKE_CURRENT_BINARY_DIR}/generated/")
write_compiler_detection_header(
    FILE "${gen_include}/${PROJECT_NAME}/detection.hpp"
    PREFIX ${PROJECT_NAME}
    COMPILERS Clang MSVC
    FEATURES cxx_variadic_templates
    VERSION 3.10
)

add_executable(foo foo.cpp)
target_include_directories(
    foo PUBLIC "$<BUILD_INTERFACE:${gen_include}>"
)

// foo.cpp
#include <foo/detection.hpp>

int main() {
}

Will return error while compiling with GCC:

/usr/bin/g++ ... -c /.../foo.cpp
In file included from /.../foo.cpp:2:0:
/.../generated/foo/detection.hpp:192:6: error: #error Unsupported compiler
 #    error Unsupported compiler
      ^

Compiler identification relies on CMAKE_<LANG>_COMPILER_ID which is not guaranteed to be set by CMake. From documentation:

This variable is not guaranteed to be defined for all compilers or languages.