Rust-analyzer stopped correctly handle adding new members to the workspace

[bminaiev]

In the workspace with several projects, when a new project is added (e.g. by cargo new example and adding example in members list in Cargo.toml), rust-analyzer doesn't work at all in the new project until rust-analyzer is restarted.

To reproduce it is important to edit Cargo.toml with some external editor (in my actual case Cargo.toml is updated by another program automatically, and rust-analyzer doesn't notice it). In case you manually save Cargo.toml again in VSCode, it will trigger DidSaveTextDocument, which in the end does a full workspace reload and fixes the problem. But if the DidSaveTextDocument event does not happen, a new project is not analyzed by rust-analyzer.

I did some git bisect and figured out that it stopped working a week ago after this pull request #12947 by @Veykril was merged.

As I understand previously it worked like this. After creating a new project (say example), adding it to the Cargo.toml, and opening example/src/main.rs in VSCode, GlobalState::process_changes is called with this file, which added something to self.fetch_workspaces_queue, and in the end, triggered workspace reload.

But in the newest version of rust-analyzer, there is an additional check that the source root of the modified file is not a library. It sounds like a reasonable check (and I'd expect rust-analyzer to think about example project as not library). As I understand the problem is when new roots are calculated, source_root_config doesn't know yet about new files, and classify them into last special file_set (which is considered as a library).

Funny enough unknown files are not always mapped into that last special file_set. For example, if project example is already present, and you add a new project, which starts from the same name (e.g. example2), FileSetConfig maps files from the new project to the old one (until it will know example2 is actually a separate thing). This probably should be also fixed.

To end this long (sorry for that) text, I don't really know what should be the correct fix for this issue (e.g. I don't really understand why rust-analyzer doesn't just watch for updates of Cargo.toml), but hope at least my findings will help somebody to fix it :)

rust-analyzer version: both current master (3903243), and current stable version (2022-08-15) doesn't work. 97038e5 worked fine.

rustc version: rustc 1.65.0-nightly (29e4a9e 2022-08-10)

I use Ubuntu if it matters.

[Veykril]

Hmm, I think the problem here is that the new project lands in the default source root which is not tagged as local? I honestly don't know, the source root implementation is very obscure to me and I fail to properly understand the implementation. I'll revert that part of PR for the time being I guess.