cmake error relating to REGEX and CORRADE_CXX_FLAGS

[TimYorke]

After installing Magnum using vcpkg (x64-windows), I got this error when trying to configure my cmake project:

CMake Error at C:/Users/timyo/dev/libs/vcpkg/installed/x64-windows/share/cmake/Corrade/UseCorrade.cmake:302 (string): string sub-command REGEX, mode REPLACE needs at least 6 arguments total to command. Call Stack (most recent call first): C:/Users/timyo/dev/libs/vcpkg/installed/x64-windows/share/cmake/Corrade/FindCorrade.cmake:592 (include) C:/Users/timyo/dev/libs/vcpkg/installed/x64-windows/share/cmake/Corrade/CorradeConfig.cmake:26 (include) C:/Users/timyo/dev/libs/vcpkg/scripts/buildsystems/vcpkg.cmake:439 (_find_package) C:/Users/timyo/dev/libs/vcpkg/installed/x64-windows/share/cmake/Magnum/FindMagnum.cmake:233 (find_package) C:/Users/timyo/dev/libs/vcpkg/installed/x64-windows/share/cmake/Magnum/MagnumConfig.cmake:26 (include) C:/Users/timyo/dev/libs/vcpkg/scripts/buildsystems/vcpkg.cmake:439 (_find_package) CMakeLists.txt:6 (find_package)

I guessed that it was because CORRADE_CXX_FLAGS wasn't set, and worked around it by adding a check for this before the REGEX command.

[mosra]

Hi!

I looked into UseCorrade.cmake and can't find a code path that would result in empty/unset CORRADE_CXX_FLAGS. Are you using a compiler other than MSVC or clang-cl?

In any case, I think the following patch should make it work without an additional check -- can you confirm?

diff --git a/modules/UseCorrade.cmake b/modules/UseCorrade.cmake
index 8276c71a..34188016 100644
--- a/modules/UseCorrade.cmake
+++ b/modules/UseCorrade.cmake
@@ -299,7 +299,7 @@ if(CORRADE_BUILD_DEPRECATED)
     string(REPLACE ";" " " CORRADE_CXX_FLAGS "${CORRADE_CXX_FLAGS}${CORRADE_PEDANTIC_COMPILER_OPTIONS}")
 
     # Remove generator expressions that distinct between C and C++
-    string(REGEX REPLACE "\\$<\\$<STREQUAL:\\$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:([^>]+)>" "\\1" CORRADE_CXX_FLAGS ${CORRADE_CXX_FLAGS})
+    string(REGEX REPLACE "\\$<\\$<STREQUAL:\\$<TARGET_PROPERTY:LINKER_LANGUAGE>,CXX>:([^>]+)>" "\\1" CORRADE_CXX_FLAGS "${CORRADE_CXX_FLAGS}")
 endif()
 
 # Provide a way to distinguish between debug and release builds via

[TimYorke]

Hi Mosra. I can confirm your patch works fine. As for why CORRADE_CXX_FLAGS is empty, I haven't investigated, but this is my CMakeLists.txt if it helps (I'm using MSVC):

cmake_minimum_required(VERSION 3.0.0)
cmake_policy(SET CMP0054 OLD)
project(LearnOpenGL VERSION 0.1.0 LANGUAGES CXX)  
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

find_package(Magnum CONFIG REQUIRED Sdl2Application Shaders GL Trade MeshTools Primitives AnySceneImporter)
include_directories(${PROJECT_SOURCE_DIR}/src)
include_directories(${MAGNUM_INCLUDE_DIR})
set_directory_properties(PROPERTIES CORRADE_USE_PEDANTIC_FLAGS ON)

file(GLOB_RECURSE SOURCES
    src/*.cpp
)

add_executable(LearnOpenGL ${SOURCES})
set_property(TARGET LearnOpenGL PROPERTY CXX_STANDARD 20)
SET_PROPERTY (TARGET LearnOpenGL PROPERTY CXX_STANDARD_REQUIRED ON)

target_link_libraries(LearnOpenGL PRIVATE Magnum::Magnum Magnum::Application Magnum::Shaders Magnum::GL Magnum::Trade Magnum::MeshTools Magnum::Primitives Magnum::AnySceneImporter)

[mosra]

Oh, the CMP0054 might actually be the culprit. Can you try with

cmake_minimum_required(VERSION 3.4) # minimum required by Magnum
# no cmake_policy(SET CMP0054 OLD)

instead? That way it should work even without the above patch.

[TimYorke]

Okay. First I tried the configure step without setting the CMP0054 policy but that made no difference except for also producing a lot of CMP0054-related warnings.
Then I tried changing the minimum cmake version from 3.0 to 3.4 and that stopped both the CMP0054 warnings and the REGEX error in one hit.
It was my mistake - I didn't know that the cmake_minimum_required() command actually changes cmake's behaviour by implicitly invoking cmake_policy().

Sorry for the false alarm and thanks for your help.

[TimYorke]

The problem was caused by calling cmake_minimum_required() with the wrong version

[mosra]

No problem -- I think this error could still happen with unrecognized compilers (such as ICC), so I commited the patch as mosra/corrade@5aa75d4. Thanks for testing it! 👍