Extend VFS to allow dynamic addition of source roots

[matklad]

Currently, VFS requires the set of roots in its new. Ideally, we should allow to dynamically add source roots.

This is tricky, however: an added root can be withing some previously existing root, so we'll need to move files from the old root to the new one. (so, both Remove & Add files in the pending_changes).

Another thing to keep in mind is that we can add a new, nested root when the old root is being scanned! So, we need to account for that as well.

The relevant code is here: https://github.com/rust-analyzer/rust-analyzer/blob/1491fafddbe16bb5851c7ad8f82011e224e469ed/crates/ra_vfs/src/lib.rs#L119

[pasa]

I would like to do this. As I understand vfs was moved to the separate repo. Do you have some best practice manage with multiple repo in this project?

[matklad]

Vfs is indeed in a separate repo: https://github.com/rust-analyzer/ra_vfs

We publish it to crates.io and use a usual cargo dependency.

For hackig, it's a good idea to add something like

ra_vfs = { path = "../ra_vfs" }

to the [patch] section in the root Cargo.toml.

I am not actually sure it is a best issue to work on right now: there's hope that the new notify (file watching crate we use) will implement an API which will make VFS implementation much more straitforward. If that happens, we'll perhaps will need to re-think how code is split between vfs and rust-analyzer.

I'd even say that the best way to move this issue forward is to hack on notify to add 175.

[pasa]

Ok. It is pity, but seems that all another e-mentor issues are taken. Will try to find something I can cope with.

[matklad]

I think is obsoleted, we should re-design VFS API based on https://docs.rs/watchman_client/0.4.0/watchman_client/