Issue compiling ishapes with CMake: try_compile() works only for enabled languages.

[floatingbit]

I was able to successfully compile OpenDDS-DDS-3.30/OpenDDS-3.30 using Ubuntu 20.04/22.04 LTS, CMake 3.27/3.31, g++ 9/10 and run the messenger example.

However, while compiling OpenDDS-DDS-3.30/examples/DCPS/ishapes source, I get the following error:

/OpenDDS-DDS-3.30/examples/DCPS/ishapes$ cmake .
--   Using OpenDDS 3.30.0 at /OpenDDS-DDS-3.30
--   Using MPC at /OpenDDS-DDS-3.30/ACE_wrappers/MPC
--   Using ACE 6.5.21 at /OpenDDS-DDS-3.30/ACE_wrappers
--   Using TAO 2.5.21 at /OpenDDS-DDS-3.30/ACE_wrappers/TAO
CMake Error at /OpenDDS-DDS-3.30/cmake/init.cmake:181 (try_compile):
  Unknown extension ".cpp" for file

    /OpenDDS-DDS-3.30/cmake/test_cxx_std.cpp

  try_compile() works only for enabled languages.  Currently these are:

    

  See project() command to enable other languages.
Call Stack (most recent call first):
  /OpenDDS-DDS-3.30/cmake/init.cmake:313 (_opendds_set_cxx_std)
  /OpenDDS-DDS-3.30/cmake/OpenDDSConfig.cmake:17 (include)
  CMakeLists.txt:2 (find_package)


CMake Error at /OpenDDS-DDS-3.30/cmake/init.cmake:294 (message):
  ACE 6.5.21 (cxx11=TRUE) requires at least C++ 2011, but compiler only
  supports up to C++ 1998.
Call Stack (most recent call first):
  /OpenDDS-DDS-3.30/cmake/init.cmake:313 (_opendds_set_cxx_std)
  /OpenDDS-DDS-3.30/cmake/OpenDDSConfig.cmake:17 (include)
  CMakeLists.txt:2 (find_package)


-- Configuring incomplete, errors occurred!

TIA

[iguessthislldo]

This is the real issue: try_compile() works only for enabled languages.

Try switching around these two lines:

OpenDDS/examples/DCPS/ishapes/CMakeLists.txt

Lines 2 to 3 in 1aa7ae0

	find_package(OpenDDS REQUIRED)
	project(ishapes VERSION ${OpenDDS_VERSION} LANGUAGES CXX)

So it's:

project(ishapes VERSION ${OpenDDS_VERSION} LANGUAGES CXX)
find_package(OpenDDS REQUIRED) 

For me it gives a warning about the VERSION keyword, but it configured and built for me just fine.

For the real fix I think this has two parts to it:

1. It obviously needs an explicit enable_language(CXX). I think I avoided doing things like this unless they were necessary, but we already need to do it for C, so maybe we should just do an enable_language(C CXX) at the start of init.cmake.
2. try_compile code looks like this:
   

   OpenDDS/cmake/init.cmake

   Lines 173 to 191 in 1aa7ae0

   	set(cplusplus_values 201103 201402 201703 202002 202302)
   	set(test_cxx_std "${CMAKE_CURRENT_LIST_DIR}/test_cxx_std.cpp")
   	set(temp_dir "${CMAKE_CURRENT_BINARY_DIR}/opendds_test_cxx_std")
   	file(MAKE_DIRECTORY "${temp_dir}")
   	# Get the latest known default compiler C++ standard
   	set(default_cxx_std_year 1998)
   	foreach(cplusplus IN LISTS cplusplus_values)
   	try_compile(compiled
   	"${temp_dir}/cplusplus_${cplusplus}"
   	SOURCES "${test_cxx_std}"
   	COMPILE_DEFINITIONS "-DOPENDDS_TEST_CPLUSPLUS=${cplusplus}L"
   	)
   	if(compiled)
   	_opendds_cplusplus_to_year(default_cxx_std_year ${cplusplus})
   	else()
   	break()
   	endif()
   	endforeach()

   
   It's checking the C++ standard starting from C++11 up. The other issue I'm realizing is this should check if it can compile with the minimum C++ standard, in this case C++98/03. If it can't then it can give a different error.

[floatingbit]

That worked! Thank you.

Would you like me to submit a PR with this change?

[iguessthislldo]

Thanks for offering, but I'm not sure that's necessary. I wrote this code not too long ago in #4487.

Reopening though because the actual fix still needs to be done.