CMake add_compile_option() SHELL: to allow spaces in options, including generator expressions. Useful for Intel oneAPI.

CMakeLists.txt

cmake_minimum_required(VERSION 3.15)

project(opt LANGUAGES Fortran)

set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

# https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2024-2/warn.html
# SHELL: allows using
#   * spaces in compiler options (especially important for Intel oneAPI
#   * repeated option prefix, that might otherwise get deduplicated incorrectly
# https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html#compiler-language-id-and-frontend-variant
# https://cmake.org/cmake/help/latest/command/add_compile_options.html#option-de-duplication

add_executable(double_opt implicit.f90)

if(WIN32)
target_compile_options(double_opt PRIVATE "$<$<Fortran_COMPILER_ID:Intel,IntelLLVM>:SHELL:/warn:all;SHELL:/warn:errors>")
else()
target_compile_options(double_opt PRIVATE "$<$<Fortran_COMPILER_ID:Intel,IntelLLVM>:SHELL:-warn all;SHELL:-warn errors>")
endif()

add_executable(single_opt implicit.f90)
# simpler way to express same options
if(WIN32)
target_compile_options(single_opt PRIVATE "$<$<Fortran_COMPILER_ID:Intel,IntelLLVM>:SHELL:/warn:all,errors>")
else()
target_compile_options(single_opt PRIVATE "$<$<Fortran_COMPILER_ID:Intel,IntelLLVM>:SHELL:-warn all,errors>")
endif()

# auto-ignore build directory
file(GENERATE OUTPUT .gitignore CONTENT "*")

message(STATUS "See file ${CMAKE_CURRENT_BINARY_DIR}/compile_commands.json for final compiler options")

implicit.f90

program main

x = 1.0

end program