Targets may build with a different edition when imported into a different workspace

[silas-enf]

For a concrete example of the problem, see dtolnay/cxx#1031.

Scenario:

• I set a rust edition default in my WORKSPACE (e.g. rust_repositories(..., edition="2021", ...))
• Another developer sets a different rust edition (e.g. "2018") in their WORKSPACE and uses that default for their rust rules
• I import and use their code in my project

(Naively) expected behavior:

• Targets from the imported repository build with edition="2018" where not overridden at the target level
• Targets from my repository build with edition="2021" where not overriden at the target level

Actual behavior:

• All targets default to edition="2021" regardless.
• Some targets which relied on edition="2018" break as a result.

My understanding is that this is a bazel limitation more than anything -- bazel doesn't consult the WORKSPACE of an imported project at all, and from what I can tell doesn't offer much of a middle ground between setting global defaults in the workspace on the one hand and requiring the argument for all targets that use it on the other.

I don't know if there's a satisfying way to fix this, but it'd be good to at least have the docs mention the limitation and mitigation.

[UebelAndre]

I believe #1256 addressed this issue so I'll close this out. @silas-enf definitely reopen this (or someone ping this issue and I can do so) if I'm mistaken!