Hi @smoofra

Thanks for your report.

I have just tried it and it works, I can do your above steps and it doesn't raise any error.

You didn't report the Conan version, so maybe you are using Conan 1? I was trying with Conan 2.
One of the aspects that Conan 2 greatly improve over Conan 1 is the graph resolution capabilities, allowing more advanced cases like this kind of bootstrapping.

I'm using conan 2.5.0

I just tried it again in a fresh environment and I still get the erorr

ubuntu 24.04, python 3.12.3

certifi==2024.7.4
charset-normalizer==3.3.2
colorama==0.4.6
conan==2.5.0
distro==1.8.0
fasteners==0.19
idna==3.7
Jinja2==3.1.4
MarkupSafe==2.1.5
patch-ng==1.17.4
python-dateutil==2.9.0.post0
PyYAML==6.0.1
requests==2.32.3
six==1.16.0
urllib3==1.26.19

I have added a dockerfile to the example
run docker build . and it should reproduce

well, I found a workaround

    def build_requirements(self):
        # when this recipe is being used as a build tool, hide all of its
        # requirements to avoid graph cycle errors due to bootstrapping
        if self.context == "build":
            return
        ....

It means that the gcc recipe can't be built using --build=missing, because the dependencies would be missing from conan.

But my gcc recipe is already only possible to build inside its own special CI pipeline anyway for reasons so this is no great loss to me

Sorry, I have limited connectivity now, can't really use docker now, but assigned it to have a look at my return.
It is possible that the if self.context == "build": is not a workaround, it sounds like a valid and correct way to break an infinite loop that would happen otherwise (I need to check it properly first, last time I couldn't reproduce)

I have been investigating this.

At the moment, it is not possible to have a dependency on the same pkg/version as the current package, being the only exception the one that does something like:

def build_requirements(self):
     if cross_building(self):
           self.tool_requires("pkg/version")

The reason it is this way is because it is very easy to fall in an infinite loop which results in the Conan application hanging forever until it exhausts and fail, which is very bad UX.

The cross_building() condition acts very much like the if self.context == "build" in your case, pre-building it in the way you do it, as it is not possible to build it as part of a larger graph with --build=missing if the package is already in the "build" context.

It is not possible then to use settings to condition in the build_requirements(), because it doesn't really break the loop, the loop is checked before that and it fails, except for the case of the change of context from host to build.

I'd say that your approach is good enough at the moment.

I am not saying that we will not try to expand the bootstrapping capabilities, I will do some experiments to check what might be possible.

This would be an experimental branch to investigate the possibilities: #16870

#16870 was merged, so this will be part of Conan 2.8. Feedback welcome!