[Discussion] [Live Share] Restrict language services to local files

[lostintangent]

In preparation for Visual Studio Live Share adding support for "guests" to receive remote language services for PowerShell, this PR simply updates the current DocumentSelector to be limited to file and untitled (unsaved) files. This way, when someone has the PowerShell extension installed, and joins a Live Share session (where files use the vsls: scheme), their language services will be entirely derived from the remote/host side, which provides a more accurate and project-wide experience (guests in Live Share don't have local file access to the project they're collaborating with).

If someone joins a PowerShell project using Live Share, and doesn't have the PowerShell extension installed, then they will automatically receive language services from the host (which is awesome! 🎉), so this PR is simply an optimization for the case where collaborating developers both have the PowerShell extension installed. Additionally, this wouldn't impact the "local" PowerShell development experience.

Note: As an example, the TypeScript/JavaScript language services that come in-box with VS Code already have this scheme restriction, and so this PR replicates that behavior.

[TylerLeonhardt]

LGTM! I'm super excited for this feature!

[rjmholt]

@SteveL-MSFT want to loop you in here — possible security considerations?

[SteveL-MSFT]

@rjmholt it doesn't seem that there's a security concern here as if I understand this change correctly, without this the guest invited to a live share would have access to the remote files already and also local files, but this change restricts the share session to just the remote files.

[lostintangent]

@SteveL-MSFT That is correct!

[rjmholt]

Ok, I've fully parsed this now. Looks like a really good change! Particularly happy that we've gotten rid of a few hard-coded strings as well.

[TylerLeonhardt]

Thanks for contributing @lostintangent!!