Pass --bin to cargo check when a binary is changed

[mo8it]

I marked this as important because it affects Rust beginners and I don't want them to get a bad expression while learning with Rustlings. It causes Rustlings to freeze for a long time because Rust-Analyzer blocks Cargo.

The issue is described here with a video: rust-lang/rustlings#2071

I was able to reproduce it in VS-Code in a Windows 10 VM (probably not a Windows problem, didn't test on Linux).

You don't even need to have Rustlings running in the background to see how Rust-Analyzer rebuilds everything on every file save:

• Initialize Rustlings with rustlings inti
• Open VS-Code in the generated rustlings/ directory
• Wait for Rust-Analyzer to be done
• Open a file and trigger a save
• See that Rust-Analyzer rebuilds all 188 binaries!

It looks like an issue in the Rust-Analyzer VS-Code plugin because it doesn't happen in Helix in the same VM.

The effect probably became more dramatic after I added --keep-going in #17561

[Veykril]

Which rust-analyzer version are you using with your helix setup? (wanna make sure whether its vscode specific or your helix r-a is just too old)

[Veykril]

Also running CARGO_LOG=cargo::core::compiler::fingerprint=info with the appropriate cargo check command after r-a presumably invalidated the build would be good, that will tell what the cause of the invalidations is

[mo8it]

I used Rust-Analyzer as the component installed by rustup for the stable channel. But your comment made me check that version and it is indeed an older one from May. So the change in #17561 isn't applied yet. VS-Code has a recent version of Rust-Analyzer. So I made the beta channel the default which has a recent version of Rust-Analyzer. Then I also saw this issue in Helix. So it is not a VS-Code problem.

---

I disabled Rust-Analyzer and ran CARGO_LOG=cargo::core::compiler::fingerprint=info cargo check after saving a file. It showed the following for all exercises but the one changed:

0.146508600s  INFO prepare_target{force=false package_id=exercises v0.0.0 (C:\Users\vm\rustlings) target="intro2"}: cargo::core::compiler::fingerprint: fingerprint dirty for exercises v0.0.0 (C:\Users\vm\rustlings)/Check { test: false }/TargetInner { name: "intro2", doc: true, ..: with_path("C:\\Users\\vm\\rustlings\\exercises/00_intro/intro2.rs", Edition2021) }
   0.146615600s  INFO prepare_target{force=false package_id=exercises v0.0.0 (C:\Users\vm\rustlings) target="intro2"}: cargo::core::compiler::fingerprint:     dirty: FsStatusOutdated(Stale)

The one changed showed a changed timestamp which is expected.

I don't see why Rust-Analyzer thinks that everything is invalid.

[mo8it]

In case this is helpful, I copied the logs of Helix after saving a file:

2024-08-08T15:18:18.364 helix_lsp::transport [INFO] rust-analyzer -> {"jsonrpc":"2.0","method":"textDocument/formatting","params":{"options":{"insertSpaces":true,"tabSize":4},"textDocument":{"uri":"file:///C:/Users/vm/rustlings/exercises/03_if/if1.rs"}},"id":1}
2024-08-08T15:18:18.504 helix_lsp::transport [INFO] rust-analyzer <- {"jsonrpc":"2.0","id":1,"result":null}
2024-08-08T15:18:18.504 helix_lsp::transport [INFO] rust-analyzer <- null
2024-08-08T15:18:18.522 helix_lsp::transport [INFO] rust-analyzer -> {"jsonrpc":"2.0","method":"textDocument/didSave","params":{"textDocument":{"uri":"file:///C:/Users/vm/rustlings/exercises/03_if/if1.rs"}}}
2024-08-08T15:18:18.523 helix_lsp::transport [INFO] rust-analyzer -> {"jsonrpc":"2.0","method":"workspace/didChangeWatchedFiles","params":{"changes":[{"type":2,"uri":"file:///C:/Users/vm/rustlings/exercises/03_if/if1.rs"}]}}
2024-08-08T15:18:18.592 helix_lsp::transport [INFO] rust-analyzer <- {"jsonrpc":"2.0","id":21,"method":"window/workDoneProgress/create","params":{"token":"rust-analyzer/flycheck/0"}}
2024-08-08T15:18:18.592 helix_lsp::transport [INFO] rust-analyzer <- {"jsonrpc":"2.0","method":"$/progress","params":{"token":"rust-analyzer/flycheck/0","value":{"kind":"begin","title":"cargo check","cancellable":true}}}
2024-08-08T15:18:18.597 helix_lsp::transport [INFO] rust-analyzer -> {"jsonrpc":"2.0","result":null,"id":21}
2024-08-08T15:18:18.925 helix_lsp::transport [INFO] rust-analyzer <- {"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"uri":"file:///c:/Users/vm/rustlings/exercises/15_traits/traits2.rs","diagnostics":[]}}
2024-08-08T15:18:18.925 helix_lsp::transport [INFO] rust-analyzer <- {"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"uri":"file:///c:/Users/vm/rustlings/exercises/15_traits/traits3.rs","diagnostics":[]}}

… (A message for every diagnostic in every binary)

2024-08-08T15:18:28.681 helix_lsp::transport [INFO] rust-analyzer <- {"jsonrpc":"2.0","method":"$/progress","params":{"token":"rust-analyzer/flycheck/0","value":{"kind":"end"}}}

As you can see, it takes 10 seconds in the Windowns VM with 2 CPUs until the checks are done although nothing was changed, only a file save was triggered.

In case you try to reproduce it: The effect isn't dramatic if Rust-Analyzer is running on bare metal with 16 threads. It is bad if someone has an older PC.

[mo8it]

Maybe there is no invalidation problem here. When I run cargo check in the VM, it takes about 10 seconds too because of the 188 binaries.

@Veykril Does Rust-Analyzer run cargo check without specifying a binary every time a binary changes? If yes, then that is the problem. It should only run cargo check --bin BINARY_NAME.

[Veykril]

Ye I think you are right, there is no invalidation here. By default we run check with --workspace, try setting rust-analyzer.check.workspace to false, that should fix this I then I think

[mo8it]

I just tried setting rust-analyzer.check.workspace to false in Helix and VS-Code but it didn't help. Its documentation says that it passes -p instead of --workspace. But Rustlings is one package with 188 binaries. We need some option to pass --bin when a binary is changed, not -p or --workspace. That should be enabled by default. I would hate to tell beginners to change settings of their language server.

[Veykril]

That should be enabled by default. I would hate to tell beginners to change settings of their language server.

We won't change the default for this, as imo that is a worse default than what we have there right now. We do have a rust-analyzer.toml which should allow (if not yet, then that needs to change) setting that relevant setting for the generated rustlings workspace.

Though given all of these are binaries you are raising an interesting point, --workspace config enabled or not, when only a binary source file changes/gets saved, we should always only check that binary as it can't have other crates depend on it anyways (likewise for examples and integration tests I think?)!

[Veykril]

(Though that will require some bigger changes to the flychecking infra unfortunately)

[mo8it]

@alibektas Since you assigned yourself: Did you already start working on it? I wanted to try implementing it myself and start tomorrow if you don't mind. Otherwise, I would be happy to review (if my review counts).

[alibektas]

@alibektas Since you assigned yourself: Did you already start working on it? I wanted to try implementing it myself and start tomorrow if you don't mind. Otherwise, I would be happy to review (if my review counts).

@mo8it I tried one or two things myself but I don't really have anything concrete atm. If you want to implement it yourself I have nothing against it. But let me also offer that I can try getting it done today and if I can't you can take over. How does that sound?

[mo8it]

@alibektas Sounds good! I won't be able to start before tomorrow night anyway ;)

[alibektas]

@mo8it 👋 I happened to solve this issue while working on a similar one. I want to honor my promise and let you submit the PR, but if you don't have anything ready yet, I could make the PR instead. Let me know what you think.

[mo8it]

Nice! No, go ahead. I didn't find time for it 😅