Can messages in CMakeLists.txt be optional?

[Unarelith]

In the CMakeLists.txt, could it be possible to add a variable to toggle the display of those messages?

entt/CMakeLists.txt

Lines 40 to 43 in dfc1861

	message("*")
	message("* ${PROJECT_NAME} v${PROJECT_VERSION} (${CMAKE_BUILD_TYPE})")
	message("* Copyright (c) 2017-2020 Michele Caini <michele.caini@gmail.com>")
	message("*")

entt/CMakeLists.txt

Line 66 in dfc1861

message(WARNING "The option USE_LIBCPP is set (by default) but libc++ is not available. The flag will not be added to the target.")

From all the libraries I'm using in my project, EnTT is the only one to talk about itself in the CMake log:

 $ cmake -B build .; and cmake --build build -j8
-- Submodule update
*
* EnTT v3.4.0 (RelWithDebInfo)
* Copyright (c) 2017-2020 Michele Caini <michele.caini@gmail.com>
*
CMake Warning at external/entt/CMakeLists.txt:66 (message):
  The option USE_LIBCPP is set (by default) but libc++ is not available.  The
  flag will not be added to the target.


-- Configuring done
-- Generating done
-- Build files have been written to: /home/bazin_q/Projects/Games/OpenMiner/build
[  9%] Built target sfml-system
[ 37%] Built target gamekit
[ 43%] Built target sfml-network
[ 55%] Built target openminer_common
[ 75%] Built target openminer_server_lib
[ 76%] Built target openminer_server
[100%] Built target openminer

against:

 $ cmake -B build .; and cmake --build build -j8
-- Submodule update
-- Configuring done
-- Generating done
-- Build files have been written to: /home/bazin_q/Projects/Games/OpenMiner/build
[  9%] Built target sfml-system
[ 37%] Built target gamekit
[ 43%] Built target sfml-network
[ 55%] Built target openminer_common
[ 75%] Built target openminer_server_lib
[ 76%] Built target openminer_server
[100%] Built target openminer

[skypjack]

I think that setting the cmake's message mode to VERBOSE is enough. Does it solve your problem?

[Unarelith]

For the first messages, setting message to VERBOSE is fine, thanks.

However about this change:

option(USE_LIBCPP "Use libc++ by adding -stdlib=libc++ flag if availbale." OFF)

• I think it should stay ON, but if you want to keep it OFF you'll also need to remove the (by default) in the warning message
• There was a typo "availbale" -> "available"

I think that a good way to make this warning optional would be to add a variable to toggle it.

[skypjack]

I think it should stay ON

Yeah, I thought the same yesterday. I'm changing it soon.

I think that a good way to make this warning optional would be to add a variable to toggle it.

Well, in fact, there exists already a way to toggle it. You can set the USE_LIBCPP option to OFF. Doesn't it work for you?

[Unarelith]

Well, in fact, there exists already a way to toggle it. You can set the USE_LIBCPP option to OFF. Doesn't it work for you?

I still want to use libc++ by default, but I don't want the warning to appear each time I run cmake. :/

[skypjack]

Oh, I see what you mean. You distribute your application, so you don't know what's on the target platform and you don't want to set an option to OFF by default.
I think we can safely set also that message to VERBOSE rather than to WARNING. I don't see any problem with this. It's informative but it doesn't cause any problem.

[Unarelith]

Debian 9 and Ubuntu 16 users needs to either upgrade their libstdc++ (not trivial) or install libc++ to have a C++17-compliant library. That's why I think ON is the best default value for that option.

Setting this message to verbose could be a way to do it, yes, since you'll still see:

-- Performing Test HAS_LIBCPP
-- Performing Test HAS_LIBCPP - Failed

But setting it to verbose makes it less noticeable for people that actually cares about the warning. That's why I though a specific variable to disable the warning would be a nice way.

Some users could do set(USE_LIBCPP_WARN OFF) or something alike to disable the warning, while other people will still get the expected result.

But it's just my opinion.