CMakeLists.txt: Fix build on modern *nix systems w/C++17

[trinitronx]

This fixes #104

• Use C++17 in CMakeLists.txt
• Use "NEW" BoostConfig.cmake policy (CMP0167)
• Change ordering of project() after cmake_minimum_required() - Similar to fix described in #102

[!NOTE]

For those who can't wait for this PR to be merged, but need a working darling-dmg on affected Arch-based distro family systems:

See this forked PKGBUILD which includes this patch

[bugaevc]

/usr/include/unicode/unistr.h and /usr/include/unicode/localpointer.h, which is where compilation fails according to https://github.com/darlinghq/darling-dmg/issues/104, appear to be a part of libicu? Does libicu hard-require you to use C++17 now?

[trinitronx]

/usr/include/unicode/unistr.h and /usr/include/unicode/localpointer.h, which is where compilation fails according to #104, appear to be a part of libicu?

Yes, it looks like /usr/include/unicode/unistr.h is part of libicu (Arch package: core/icu), which is currently version 75.1:

$ pacman -Fx /usr/include/unicode/unistr.h
usr/include/unicode/unistr.h is owned by core/icu 75.1-1
$ pacman -Fx /usr/include/unicode/localpointer.h
usr/include/unicode/localpointer.h is owned by core/icu 75.1-1

Does libicu hard-require you to use C++17 now?

I'm not sure, but the errors relating to std::enable_if_t might need at least C++14:

error: ‘std::enable_if_t’ has not been declared.

Yet, when I tried using set(CMAKE_CXX_STANDARD 14), there were some other errors:

C++14 Build Log

```console $ mkdir build && cd build $ cmake ../ -DCMAKE_INSTALL_PREFIX=/usr -DWITH_TESTS=1 -DCMAKE_BUILD_TYPE=Release -- The C compiler identification is GNU 14.2.1 -- The CXX compiler identification is GNU 14.2.1 -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working C compiler: /usr/bin/cc - skipped -- Detecting C compile features -- Detecting C compile features - done -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Check for working CXX compiler: /usr/bin/c++ - skipped -- Detecting CXX compile features -- Detecting CXX compile features - done -- Found PkgConfig: /usr/bin/pkg-config (found version "2.1.1") -- Found LibXml2: /usr/lib/libxml2.so -- Configuring done (0.3s) -- Generating done (0.0s) -- Build files have been written to: /home/exampleuser/src/pub/darling-dmg/build $ make [ 3%] Building CXX object CMakeFiles/CacheTest.dir/test/CacheTest.cpp.o [ 6%] Building CXX object CMakeFiles/CacheTest.dir/src/CacheZone.cpp.o [ 9%] Building CXX object CMakeFiles/CacheTest.dir/src/CachedReader.cpp.o [ 12%] Building CXX object CMakeFiles/CacheTest.dir/src/Reader.cpp.o [ 15%] Building CXX object CMakeFiles/CacheTest.dir/src/MemoryReader.cpp.o [ 18%] Linking CXX executable CacheTest [ 18%] Built target CacheTest [ 21%] Building CXX object CMakeFiles/dmg.dir/src/unichar.cpp.o In file included from /usr/include/unicode/unistr.h:39, from /home/exampleuser/src/pub/darling-dmg/src/unichar.cpp:3: /usr/include/unicode/stringpiece.h:134:23: error: ‘is_same_v’ is not a member of ‘std’; did you mean ‘is_same’? 134 | (std::is_same_v | ^~~~~~~~~ | is_same /usr/include/unicode/stringpiece.h:134:66: error: template argument 1 is invalid 134 | (std::is_same_v | ^ /usr/include/unicode/stringpiece.h:138:17: error: expected ‘>’ before ‘)’ token 138 | ) && | ^ /usr/include/unicode/stringpiece.h:138:17: error: expected unqualified-id before ‘)’ token In file included from /usr/include/unicode/uenum.h:25, from /usr/include/unicode/ucnv.h:52, from /home/exampleuser/src/pub/darling-dmg/src/unichar.cpp:4: /usr/include/unicode/localpointer.h:561:26: error: ‘auto’ parameter not permitted in this context 561 | template | ^~~~ /usr/include/unicode/localpointer.h:573:76: error: template argument 2 is invalid 573 | explicit LocalOpenPointer(std::unique_ptr &&p) | ^ /usr/include/unicode/localpointer.h:583:78: error: template argument 2 is invalid 583 | LocalOpenPointer &operator=(std::unique_ptr &&p) { | ^ /usr/include/unicode/localpointer.h:599:59: error: template argument 2 is invalid 599 | operator std::unique_ptr () && { | ^ /usr/include/unicode/uenum.h:69:1: note: invalid template non-type parameter 69 | U_DEFINE_LOCAL_OPEN_POINTER(LocalUEnumerationPointer, UEnumeration, uenum_close); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/include/unicode/ucnv.h:597:1: note: invalid template non-type parameter 597 | U_DEFINE_LOCAL_OPEN_POINTER(LocalUConverterPointer, UConverter, ucnv_close); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ make[2]: *** [CMakeFiles/dmg.dir/build.make:76: CMakeFiles/dmg.dir/src/unichar.cpp.o] Error 1 make[1]: *** [CMakeFiles/Makefile2:113: CMakeFiles/dmg.dir/all] Error 2 make: *** [Makefile:146: all] Error 2 ```

I bumped it to C++17, and then it compiled fine.

[trinitronx]

Does libicu hard-require you to use C++17 now?

@bugaevc: For what it's worth, that second set of errors when trying C++14 was also mentioning files from the icu package:

/usr/include/unicode/stringpiece.h:134:23: error: ‘is_same_v’ is not a member of ‘std’;

$ pacman -Fx /usr/include/unicode/stringpiece.h
usr/include/unicode/stringpiece.h is owned by core/icu 75.1-1

So, given that there are no standards supported by gcc's -std= between c++14 and c++17... I suppose it would be safe to assume that current versions of libicu require at least the C++ 2017 standard.

EDIT: According to the icu.unicode.org website, C++ 17 is now required for version 75

2024-04-17: ICU 75 is now available. It updates to CLDR 45 (beta blog) locale data with new locales and various additions and corrections. C++ code now requires C++17 and is being made more robust. The CLDR MessageFormat 2.0 specification is now in technology preview, together with a corresponding update of the ICU4J (Java) tech preview and a new ICU4C (C++) tech preview. See Downloading ICU > ICU 75.