Rust With Claude Code

Rust with Claude Code

Session Startup Checklist

Every Rust session:

cd core/pd-console
cargo check           # fast semantic check (catches 90% of errors)
cargo clippy          # lints (catches real bugs, not just style)
cargo test --bin pd-console-repl  # unit tests

Tell Claude your current test status first: "cargo check passes, clippy clean, 23 tests green."

Sharing Errors with Claude

Always share:

1. Full compiler error (all lines, not just the first)
2. 10-15 lines of surrounding code
3. One sentence of intent: "I want to [read field], then [mutate struct]"

Claude pattern-matches on constraint shape, not syntax. Intent enables correct suggestions.

Borrow Checker Patterns

Get field → use → mutate struct:

// WRONG: borrow extends into mutation
let channel = &self.agents[i].channel;
self.agents[i].cursor = 0;  // ERROR: still borrowed

// RIGHT: scope the borrow
let channel = self.agents[i].channel.clone();
self.agents[i].cursor = 0;

Self reference in async closure:

// RIGHT: extract into owned bindings, then use
let (channel, backend) = {
    let a = self.agents.get(&local)?;
    (a.channel.clone(), a.backend)
};
self.client.tube_send(&channel, text, "operator").await

Modify while iterating:

// Collect indices, apply after
let to_remove: Vec<_> = self.items.iter().enumerate()
    .filter(|(_, item)| item.should_remove())
    .map(|(i, _)| i)
    .collect();
for i in to_remove.into_iter().rev() {
    self.items.remove(i);
}

Async Patterns for pd-console

Thread + tokio mini-runtime for HTTP (main.rs pattern):

let (tx, rx) = mpsc::channel::<Vec<Block>>();
std::thread::spawn(move || {
    let rt = tokio::runtime::Builder::new_current_thread()
        .enable_all().build().expect("tokio rt");
    rt.block_on(async move {
        loop {
            tokio::time::sleep(Duration::from_secs(2)).await;
            if tx.send(data).is_err() { break; }  // window closed
        }
    });
});

Use ALWAYS for reqwest: it needs tokio; GPUI uses smol. Never run reqwest in GPUI's executor.

Async trait method (object-safe, no async-trait crate):

fn refresh<'a>(
    &'a mut self,
    daemon: &'a DaemonClient,
) -> std::pin::Pin<Box<dyn std::future::Future<Output = Result<()>> + Send + 'a>> {
    Box::pin(async move {
        // async code
    })
}

Async tests:

#[tokio::test]
async fn test_refresh() {
    let client = DaemonClient::new("http://localhost:9999".into());
    assert!(client.agents().await.is_err());  // no daemon, should fail gracefully
}

Use #[tokio::test] for async — never #[test] on an async fn.

Testing Patterns

Unit tests in the same file:

#[cfg(test)]
mod tests {
    use super::*;  // Access private types

    fn make_pane(entries: Vec<Entry>) -> MyPane {
        MyPane { entries, count: 0, last_error: None }
    }

    #[test]
    fn view_empty() {
        assert!(!make_pane(vec![]).view().is_empty());
    }

    #[test]
    fn view_error_state() {
        let mut p = MyPane::default();
        p.last_error = Some("conn refused".into());
        let blocks = p.view();
        assert!(blocks.iter().any(|b| matches!(b, Block::KeyVal(k, _) if k == "error")));
    }
}

Test three states always: empty, populated, error.

CI constraint: cargo test --bin pd-console-repl with RUST_MIN_STACK=16777216 (GPUI proc-macros overflow Linux rustc stack on --lib test mode).

Error Handling (anyhow)

use anyhow::{anyhow, Context, Result};

pub async fn fetch(&self, path: &str) -> Result<Value> {
    let resp = self.http
        .get(format!("{}{}", self.base, path))
        .send()
        .await
        .context(format!("GET {}", path))?;  // Add context to any error
    
    let v: Value = resp.json().await.context("parse JSON")?;
    Ok(v)
}

Always .context("what were we doing") — makes error chains readable. Never .unwrap() outside tests.

Clippy Rules

Meaningful (fix these):

• borrowed_box → use &T not &Box<T>
• clone_on_copy → Copy types use copy, not .clone()
• unwrap_used → use ? or .ok_or_else() in non-test code

Safe to ignore in GPUI code:

• type_complexity → GPUI builders create complex element types by design
• upper_case_acronyms → PD/API naming is intentional

String Efficiency

Avoid String::from("text") — use "text".into() or .to_string() for clarity at call site.

Cargo Workflow

cargo watch -x check        # Continuous check on file save
cargo check                 # Fast semantic check
cargo clippy                # Lints + real bug detection
cargo test                  # All tests
cargo run --bin pd-console  # Run the GPUI app
cargo fmt                   # Format before commit

Feature flags explicit:

tokio = { version = "1", features = ["rt-multi-thread", "macros", "time", "sync"] }
reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }

Never leave features implicit — it makes AI assistance and debugging harder.

What to Push Back on When Claude Suggests

• ✗ .unwrap() → "Use ? or .ok_or_else()"
• ✗ async-trait crate → "We use Box::pin(async { ... }) for object safety"
• ✗ Arc<Mutex<T>> → "We use mpsc channels — Arc blocks the renderer"
• ✗ #[test] on async fn → "Use #[tokio::test] for async tests"
• ✗ Modifying self during render → "GPUI renders are pure; mutate in event handlers"

Trait Object Pattern (Pane registry)

pub trait Pane: Send {
    fn id(&self) -> &str;
    fn view(&self) -> Vec<Block>;
    fn refresh<'a>(&'a mut self, daemon: &'a DaemonClient)
        -> Pin<Box<dyn Future<Output = Result<()>> + Send + 'a>>;
}

// Registry holds any Pane implementation
struct PaneRegistry {
    panes: Vec<Box<dyn Pane>>,
}

Use for plugin-like extensibility where multiple types implement the same interface. No generics needed at the registry level.

Visibility Conventions

pub struct DaemonClient { ... }        // Public to whole workspace
pub(crate) fn extract_text(...) { }   // Public within this crate
fn tone_rgb(...) { }                   // Private to module

For a binary crate (not library), most types can be pub(crate). Reserve pub for types that may be used from other crates in the workspace.

Skill Bundle Index

Every file in this skill, and when to open it. Auto-generated; run scripts/index_references.py --fix.