Feature: set CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON

[SSE4]

closes: #8582
/cc @mpusz
Changelog: Feature: Set CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON.
Docs: omit

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[solvingj]

It seems to me that this should be controlled via [conf]. As @SSE4 has said in the past, if many people using CMake try to move over to the toolchain generator and it turns out this behavior is breaking for them, it would be great if they had a way to opt-out right away.

[solvingj]

Consider adding [conf] item for this.

[memsharded]

Sounds good, lets add a [conf] to opt-out this behavior, I'd suggest something like:

[conf]
tools.cmake.cmaketoolchain:find_package_prefer_config=False

[SSE4]

now CMAKE_FIND_PACKAGE_PREFER_CONFIG is controlled by tools.cmake.cmaketoolchain:find_package_prefer_config

[SSE4]

two notes:

• right now, conanfile.conf always returns string, so it returns string value "True" instead of boolean True. I am not sure if it will be always the same, so I check type for the safety
• I believe it should be a function (just like to_meson_value), but I guess we will do it to address [feature] Binary Conan options should be expressed as an option() in CMake when generated with CMakeToolchain #8638 anyway

[memsharded]

This is not opting-out, it is opting-in please recall my comment:

Sounds good, lets add a [conf] to opt-out this behavior, I'd suggest something like

Then simplify code, as you said they are always strings, so go for a oneliner:

if self.find_package_prefer_config is not None:
    self.find_package_prefer_config = "OFF" if self.find_package_prefer_config.lower() in ("false", "0", "off") else "ON"

[SSE4]

I am not sure I understand. this is opt-out, the behavior matches CMake exactly:

• conf not defined -> CMAKE_FIND_PACKAGE_PREFER_CONFIG not defined
• conf=True -> CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON
• conf=False -> CMAKE_FIND_PACKAGE_PREFER_CONFIG=OFF

[mpusz]

The whole idea was to have it ON by default so inexperienced users using conanfile.txt without any conf sections have a friendly dev env. Advanced users may want to disable it if they so desire.

As a side note, still there are many inexperienced users out there both for Conan and CMake. Doing things that we consider trivial is not easy for them at all. For the last two days, I am remotely helping one of them to enable mp-units support via conanfile.txt even though I thought that my docs are clear: https://mpusz.github.io/units/usage.html#conan-cmake-release. Today I finally saw that person's CMake file and it turned out to be:

[SSE4]

okay, I added the ON as default again. there was a confusion because initially I implemented ON as default, then others said it should be controlled by conf instead. hopefully the current behavior makes sense:

• conf not defined -> CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON
• conf=True -> CMAKE_FIND_PACKAGE_PREFER_CONFIG=ON
• conf=False -> CMAKE_FIND_PACKAGE_PREFER_CONFIG=OFF

(although it's not exactly an opt out for the default CMake behavior, it should help for your case)

[mpusz]

Actually, in this case, a user correctly applied CONFIG REQUIRED as suggested in my docs. The problem was with the last two lines 😉

[memsharded]

@SSE4 my request was:

Sounds good, lets add a [conf] to opt-out this behavior, I'd suggest something like:

A config required to opt-out. That means that by default it is ON, and you need to do something proactively to opt-out of that feature. If you need to define a conf for activating the feature, it is not an opt-out feature, it is an opt-in feature.