[question] Correct way to conditionally depend on libjpeg-turbo or libjpeg

[HappySeaFox]

What is your question?

Hi. I'm trying to add an option in my recipe to enable JPEG. The option has three possible values: libjpeg-turbo, libjpeg, and False. I tried to implement the similar approach as other recipes (freeimage) do and enabled the libjpeg-turbo value be default in default_options:

    options = {
        ...
        "with_jpeg": ["libjpeg", "libjpeg-turbo", False],
    }
    default_options = {
        ...
        "with_jpeg": "libjpeg-turbo",
    }
    def requirements(self):
        ...
        if self.options.with_jpeg == "libjpeg-turbo":
            self.requires("libjpeg-turbo/2.1.4")
        elif self.options.with_jpeg == "libjpeg":
            self.requires("libjpeg/9e")

But the PR #14926 fails with:

ERROR: At least two recipes provides the same functionality:
 - 'libjpeg' provided by 'libjpeg-turbo/2.1.4', 'libjpeg/9e'

Am I missing anything? Any ideas?

[HappySeaFox]

It seems that the problem is that if one of my dependencies depends on libjpeg, but I explicitly ask to enable libjpeg-turbo for my recipe, there is a conflict between those two. Like that:

sail -> tiff -> libjpeg
   |
   v
libjpeg-turbo 

Is there a way to workaround that?

[SpaceIm]

Is there a way to workaround that?

yes, change default to libjpeg. It's the current default libjpeg implementation of all CCI recipes. I don't say it's a good default.

Once #14814 will be merged, we'll be able to rely on this virtual recipe and globally delegate libjpeg implementation in this recipe instead of scattering this decision to many recipes with high risk of conflicts. I also propose to change default implementation to libjpeg-turbo.