[feature] detect_api: Support detecting the version of a specific compiler about conan HOT 5 CLOSED

Proposing new detect_api.detect_xxx_compiler apis in #16092

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Hi @jwillikers - thanks for this feature request.

Bear in mind that for compilers that are not the system default, the profile needs to indicate where this compiler is located, otherwise Conan assumes that other tools just run with the system defaults as well. This is addressed by defining the tools.build:compiler_executables conf, or with [buildenv] vars where appropriate.

At the moment the detect_default_compiler() functionality is biased towards locating a default given platform priorities, or influenced by the CC/CXX environment variables - I suppose the functionality that is missing here is: if we are given a compiler executable, please fill in the rest for me.

Or alternatively, the ability to alter the priority of detect_api.detect_default_compiler() - at the moment it can already be influenced by externally to the profile file (by defining the CC environment variable when invoking Conan - this is harder to guarantee for dev machines, but it's useful for Docker images for example). However here as well we would need to ensure the profile defines the conf or env vars when used.

Otherwise, for the first option, I think the profile could look something along the lines of:

[settings]
{% set c_compiler = '/path/to/clang' %}
{% set cxx_compiler = '/path/to/clang++' %}
{% set compiler, version  = detect_api.detect_compiler_settings(cxx_compiler) %}
compiler = {{compiler}} 
compiler.version = {{version}}
# (derive other settings)


[conf]
tools.build:compiler_executables={ 'c':{{c_compiler}},'cxx':{{cxx_compiler}} }

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After the merge of #16092 an example of a profile would be the following:

[settings]
{% set c_compiler = 'clang' %}
{% set cxx_compiler = 'clang++' %}
{% set compiler, version, _ = detect_api.detect_clang_compiler(c_compiler) %}

compiler = {{compiler}}
compiler.version = {{detect_api.default_compiler_version(compiler, version)}}
compiler.libcxx = {{detect_api.detect_libcxx(compiler, version)}}
compiler.cppstd = {{detect_api.detect_cppstd(compiler, version)}}

os=Linux
arch=armv8

[conf]
tools.build:compiler_executables={ 'c':{{c_compiler}},'cxx':{{cxx_compiler}} }

from conan.

After the merge of #16092 an example of a profile would be the following:

[settings]
{% set c_compiler = 'clang' %}
{% set cxx_compiler = 'clang++' %}
{% set compiler, version, _ = detect_api.detect_clang_compiler(c_compiler) %}

compiler = {{compiler}}
compiler.version = {{detect_api.default_compiler_version(compiler, version)}}
compiler.libcxx = {{detect_api.detect_libcxx(compiler, version)}}
compiler.cppstd = {{detect_api.detect_cppstd(compiler, version)}}

os=Linux
arch=armv8

[conf]
tools.build:compiler_executables={ 'c':{{c_compiler}},'cxx':{{cxx_compiler}} }

Thanks! That's exactly what I'm looking for!

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#16092 merged for next Conan 2.3

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