Define compiler variables in CMakePresets.json

[petwu]

Changelog: Feature: Define CMAKE_<LANG>_COMPILER variables in CMakePresets.json.
Docs: Omit
Fixes #13136

The compiler variables are set to the same values as in the cmake_toolchain.cmake, and only when defining tools.build:compiler_executables.

I've tested it with both VS an VS Code, which successfully initialize the correct vcvars environment and select the correct compiler as specified by the toolset version, host and target architecture. From a non-IDE perspective, this does influence the CMake configuration in any way, as the compiler variables would be set in the toolchain to the same value anyway.

profile

[settings]
os=Windows
arch=x86
compiler=msvc
compiler.version=193
compiler.runtime=dynamic
compiler.runtime_type=Release
compiler.cppstd=17

[conf]
tools.cmake.cmaketoolchain:toolset_arch=x64
tools.build:compiler_executables={"c": "cl.exe", "cpp": "cl.exe"}

conanfile.txt

[generators]
CMakeToolchain

[layout]
cmake_layout

CMakePresets.json after conan install -pr profile -s build_type=Debug .

{
    "version": 3,
    "vendor": {
        "conan": {}
    },
    "cmakeMinimumRequired": {
        "major": 3,
        "minor": 15,
        "patch": 0
    },
    "configurePresets": [
        {
            "name": "conan-debug",
            "displayName": "'conan-debug' config",
            "description": "'conan-debug' configure using 'Ninja' generator",
            "generator": "Ninja",
            "cacheVariables": {
                "CMAKE_POLICY_DEFAULT_CMP0091": "NEW",
                "CMAKE_BUILD_TYPE": "Debug",
                "CMAKE_C_COMPILER": "cl.exe",
                "CMAKE_CXX_COMPILER": "cl.exe"
            },
            "toolset": {
                "value": "v143,host=x64",
                "strategy": "external"
            },
            "architecture": {
                "value": "x86",
                "strategy": "external"
            },
            "toolchainFile": "generators\\conan_toolchain.cmake",
            "binaryDir": "C:\\TMP\\conan-feat-presets-with-compiler\\build\\Debug"
        }
    ],
    "buildPresets": [
        {
            "name": "conan-debug",
            "configurePreset": "conan-debug",
            "jobs": 24
        }
    ],
    "testPresets": [
        {
            "name": "conan-debug",
            "configurePreset": "conan-debug"
        }
    ]
}

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• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

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[memsharded]

I think this can be moved forward for next release, thanks very much for your contribution!

Asking @jcar87 for an extra review, thanks!

[jcar87]

LGTM!

@memsharded, I would consider passing cl.exe to both C and CXX compilers if compiler=msvc, the cmake generator is Ninja, even when tools.build.compiler_executables is undefined.

[jcar87]

interesting! I've not found this documented for VS Code, but have verified that it indeed works that way. Thanks so much for figuring this out! :D

[petwu]

I thought it was documented somewhere, but I couldn't find it either and can't remember how I learned about it in the first place. But I have used this trick successfully for some time now and seeing this comment this has been a thing for at least 3 years.

[jcar87]

I can see the output is as expected, but wouldn't he compiler executables be clang or clang-cl.exe instead?

[memsharded]

I think this is being directly overriden by tools.build:compiler_executables and most likely the intention of the test was to have compiler=msvc, can you please confirm @petwu?

I'll check if it makes sense or is possible to introduce some check for this.

[memsharded]

I suspect this is derived from copy&paste the test above called test_set_cmake_lang_compilers_and_launchers

[memsharded]

Exactly, I have pushed some changes to the test to define compiler=msvc instead.
Indeed, the compiler_executables is being written no matter what the compiler setting is, it is the responsibility of the user to define the profiles consistently. I have checked if it is possible to introduce some check that made sense for potential misalignments like this one (defining compiler_executable with cl.exe for other compiler not msvc, but it looks a bit too dirty, so leaving it out of this PR, might reconsider later.

[petwu]

You are right, I just copied the test above. Setting compiler=clang and then saying your executable is called cl.exe of course doesn't make sense in a real-world scenario. The test should just verify that the compiler_executable setting ended up in the generated preset.