How to detect workspace root?

[ehuss]

A recent change (#4788) changed it so that when you run cargo from within a workspace member, the paths in messages are now relative to the workspace root instead of the member package. I work on the Sublime integration, and the tool needs to know how to resolve the relative paths so that you can jump to the appropriate file when there is an error/warning. Currently it uses a simple logic of basing paths off the package's root. However, now it needs to know the workspace root, but I am uncertain how to find that. cargo metadata doesn't seem to offer any help. Is there some heuristic I can use?

Note: Currently the build tool doesn't know whether or not it is in a workspace. It blindly runs cargo build in the directory of the package.

[alexcrichton]

Hm a good point! I actually don't think we've got a great way to learn about the workspace root, but for sure we should add it to cargo metadata!

[ehuss]

I can open a PR to add that. I have a few questions:

• What do you think of just adding a new key "workspace_root", or should it be something else?
• Does the metadata version need to change when adding keys? I would assume no, but the versioning rules don't seem to be defined.
• Would it be feasible to backport this to beta? Without it I would need to recreate all the logic in parsing manifest files which sounds unpleasant. I assume all editors/IDEs/tools which read paths will need this (if they don't already know the workspace root).

[alexcrichton]

Perhaps something like workspace_manifest: String? And yeah no need to bump the version, we'd only do that if we changed the existing version.

And sure yeah, we can backport to beta!