set jobs parameter in cmake build presets(#15419)

[Hailios]

Changelog: Feature: CMakeToolchain defines jobs in generated CMakePresets.json buildPresets.
Docs: Omit

this should be seen as a proof of concept for the feature request to have conan generate CMakePresets.json with jobs parameter set.

closes #15419

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[memsharded]

Looks good and low risk. A small unit/integration test (not really necessary a functional one) could be enough to move this forward (I have checked with the team, good to move it)

[memsharded]

Better import directly build_jobs, we are not using scoping in general.

[Hailios]

updated

[memsharded]

Great, thanks.

Did you check my comment above?

Looks good and low risk. A small unit/integration test (not really necessary a functional one) could be enough to move this forward (I have checked with the team, good to move it)

Do you think you can add some small test, it seems in https://github.com/conan-io/conan/blob/develop2/conans/test/integration/toolchains/cmake/test_cmaketoolchain.py would be the best, some of the existing ones can help? If not let me know and I'll do it

[Hailios]

would be great if you could do it :)

[memsharded]

I contributed the test, and also moved the definition to the "common" preset, so it also applies to the testPresets. I understand that we also want to do it, in the same way it affects also the CMake.test() helper?

[Hailios]

thanks for the test. very good choice of parallel jobs ;)

this should not be added to the testPresets. I do not have deep enough CMake knowledge to know why, but cmake cannot parse the same jobs parameter in the testPresets.

example invalid presets sections

    "buildPresets": [
        {
            "name": "conan-debug",
            "configurePreset": "conan-debug",
            "jobs": 16
        }
    ],
    "testPresets": [
        {
            "name": "conan-debug",
            "configurePreset": "conan-debug",
            "jobs": 16
        }
    ]

produces the following error

$ cmake --build --target all --preset conan-relwithdebinfo
CMake Error: Could not read presets from <path to root directory>:
Error: @36,21: Invalid extra field "jobs" in Preset
            "jobs": 16
                    ^

it builds in parallel with "jobs": 16 in only the buildPresets, and more importantly does not fail to read the presets.

[memsharded]

I see, yeah, lets remove it!

I'll leave jobs=42 (the answer to everything ;) only for buildPresets

[memsharded]

Merged, it will be in next 2.1, thanks for your contribution!