Feature/b2 rooted dep projects

[grisumbras]

Changelog: Fix: Allow referring to projects created by b2 generator for dependencies with absolute paths.
Docs: Omit

• Refer to the issue that supports this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.

[grisumbras]

@grafikrobot, do you have any opinion on whether this should be merged, or I should go some other direction with the fix, or maybe it's the docs that should be changed?

[lasote]

@grisumbras is there any created issue for the current PR? Could you create it?
About the PR itself, I would love @grafikrobot to take a look.

[grafikrobot]

Sorry... I was on vacation. First, this is not a bug fix. When I wrote the generator I intentionally did not make the targets global to allow multiple conan config locations. Which is something useful for large projects that have could have multiple libraries and execs using different versions of packages and still allow them to be isolated. Second, you can get the same effect by having the conan info at the root of your project, AFAIK. If that's not the case, then it would indeed be a bug. But this would not be the fix for the bug as this prevents the use case of localized package usage.

[grisumbras]

Yes, it fixes #4200. But I indeed want @grafikrobot to share his opinion, because there might be some implications I don't see, or maybe this was the intended behaviour.

[grafikrobot]

Looking at what I wrote in the docs:

For a root level project those could be referenced with an absolute project path, for example /clara.

I would suspect that if that's not working, it's a bug in b2 itself :-( And in the meantime best solution might be to change the docs to mention how to do the use-project if you want the rooted paths.

[grafikrobot]

I think the better fix is something like this (note, not tested, just eyeballing it):

if [ project.is-jamroot-module [ project-define {name} ] ]
{
    use-project /{name} : {name} ;
}

Although putting an equivalent of that in the project-define rule in the prefix would be better.

[grisumbras]

Rebased and updated to follow the suggestions. @grafikrobot, can you look at it?

[lasote]

Thanks @grafikrobot and @grisumbras for your help!