Conan: Visual Studio Compiler is recognized as C compiler but not as CXX compiler

[kutschkem]

Windows 7, Conan 1.7.4, Visual Studio 2015

I have an odd issue with my build (specifically, test_package build), where the Visual Studio compiler gets recognized as C compiler, but not as CXX compiler:

CMake log

-- The C compiler identification is MSVC 19.0.24215.1
-- The CXX compiler identification is unknown
-- Check for working C compiler using: Visual Studio 14 2015 Win64
-- Check for working C compiler using: Visual Studio 14 2015 Win64 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
CMake Error in CMakeLists.txt:
  No CMAKE_CXX_COMPILER could be found.

My profile:

[settings]
os=Windows
os_build=Windows
arch=x86_64
arch_build=x86_64
compiler=Visual Studio
compiler.version=14
compiler.runtime=MD
build_type=Release
[options]
[build_requires]
[env]

CMakeLists.txt

include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup()

add_executable(example  example.cpp)
target_link_libraries(example ${CONAN_LIBS})

To help us debug your issue please explain:

• [x] I've read the CONTRIBUTING guide.
• [x] I've specified the Conan version, operating system version and any tool that can be relevant.
• [x] I've explained the steps to reproduce the error or the motivation/use case of the question/suggestion.

[danimtb]

You profile is OK.

Looks like CMake does not recognize MSVC as a C++ compiler.
Please check your Visual Studio installation or do some of the checks suggested here https://stackoverflow.com/questions/31619296/cmake-does-not-find-visual-c-compiler

[kutschkem]

The odd thing here is that the "normal" build works without problems, it is only the test build that has an issue.

[memsharded]

Hi @kutschkem

Have you tried adding the project(MyTest CXX) in the CMakeLists.txt of the test_package folder? Please try and tell me, thanks!

[kutschkem]

This CMakeLists.txt also shows the behavior:

project(PackageTest CXX)
cmake_minimum_required(VERSION 2.8.12)

set (CMAKE_CXX_STANDARD 11)

include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup(TARGETS)

add_executable(example hello.cpp)


target_link_libraries(example CONAN_PKG::eCALMViz)

It's actually a bit strange, because I _think_ it worked before, but I changed something in one of the dependencies and now this package is also showing the symptom.

[kutschkem]

Conan version is 1.9.1, cmake version is 3.13.0

[kutschkem]

Also, this here does work, and looks very similar to the original code:

include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup()

add_executable(example example.cpp)
target_link_libraries(example ${CONAN_LIBS})

The only difference I can see is the package this belongs to.

[memsharded]

Indeed very weird. Can you reproduce it with a simple "hello world" package that you could share the complete code with us? Is it happening with the conan new Hello/0.1 -s -t + conan create . user/testing code?

[memsharded]

Hi @kutschkem

Any news here? Did you manage to reproduce it? Please tell, as we cannot reproduce here, and then there is little we could do. Thanks!

[jngrb]

I had a similar problem and could fix it by shortening the path of build folder.

Using lockfile: '__test_package\build\cb9b90f2854f038c4e3be3e555d7c730f95cf6c9/conan.lock'
Using cached profile from lockfile
rs_sys_connector/1.17.0.0@ok/qual (test package): Running build()
-- Selecting Windows SDK version 10.0.10586.0 to target Windows 10.0.17763.
-- The CXX compiler identification is unknown
CMake Error at CMakeLists.txt:3 (PROJECT):
No CMAKE_CXX_COMPILER could be found.

The normal build worked. Just the test package failed with the error above.

Apparently, the CMake compiler detection algorithm run into MAX_PATH related problems. I fixed it by reducing the length of the parent path (by 14 characters).

Using lockfile: '__test_package\build\cb9b90f2854f038c4e3be3e555d7c730f95cf6c9/conan.lock'
Using cached profile from lockfile
rs_sys_connector/1.17.0.0@ok/qual (test package): Running build()
-- Selecting Windows SDK version 10.0.10586.0 to target Windows 10.0.17763.
-- The CXX compiler identification is MSVC 19.0.24218.1
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe -- works

Nothing else was changed.

Maybe this helps here as well?

[I also remember that a virus scanner messed with the CMake compiler detection algorithm once (because some threat heuristic false-positively detected some executables that CMake builded as tests).]

[kutschkem]

Thanks, I think I might also have been at the limit regarding the path limit, so that may have factored into the problem. I have not reproduced the error since, as I did not do much work on the conan packages.

[peter-bloomfield]

I hit the same issue ("No CMAKE_CXX_COMPILER could be found"). My Conan recipe worked fine on my local Windows 10 workstation, but it failed when I tried to do exactly the same thing in an Azure pipeline on a Windows 2016 build agent.

Putting "short_paths = True" in my Conan recipe resolved it.

(It's worth noting that the build agent does not have long paths enabled for legacy reasons. Presumably enabling that would have fixed the problem too.)