New feature required to work around platform-specific source-repository-package issue

[newhoggy]

Describe the bug
Sometimes we have the situation where a package we depend only builds on a specific platform. For example libsystemd-journal only builds on Linux. We can if os(linux) in the cabal file, so that much is fine, but let's say the package has a bug in it and we want to fork it and used the fork until the bug is upstreamed. This does not work because source-repository-package adds the project to the list of local packages to always build, so cabal all no longer works, which breaks CI.

To Reproduce
Described above.

Expected behavior
This could be fixed in a number of ways. Add support for if in cabal.project would allow us to conditionally add source-repository-package. Or we could make source-repository-package not add to the list of local projects to build.

System information
Affects all versions of cabal currently.

Additional context
Work arounds include using allow-newer, for example allow-newer: libsystemd-journal:base if the problem is just a version bound adjustment.

But this does not solve the problem if the problem preventing the build from succeeding is not a bounds issue.

[georgefst]

I've just hit this, as you can see above. I guess ideally it would be closed via #5444?

[gbaz]

Yeah, looks like the same exact issue in fact. Can we close this one as a dup?

[georgefst]

I wouldn't call it the exact same issue. But #5444 is a solution to this one, and probably the best one. I guess if maintainers agree that this should be fixed by implementing #5444, then there's an argument for closing it.

[gbaz]

ok lets just note this will be resolved by #7783

[jneira]

...and as #7783 adding conditionals to cabal
project has been merged, we can close this
thanks all!