GPUI Code Quality

This skill covers best practices and code quality guidelines for GPUI development.

Error Handling

Never Use unwrap()

Rule: Avoid unwrap() and panic-inducing methods

// ❌ WRONG
let value = option.unwrap();
let result = operation().unwrap();

// ✅ CORRECT - propagate with ?
let value = option.ok_or_else(|| anyhow::anyhow!("Missing value"))?;
let result = operation()?;

// ✅ ALSO CORRECT - explicit handling
match option {
    Some(value) => {
        // Use value
    }
    None => {
        // Handle error case
    }
}

Never Silently Discard Errors

Rule: Don't use let _ = on fallible operations

// ❌ WRONG - silently discards error
let _ = client.request(url).await?;

// ✅ CORRECT - propagate error
client.request(url).await?;

// ✅ ALSO CORRECT - log but ignore
operation().log_err();

// ✅ ALSO CORRECT - explicit handling
if let Err(e) = operation() {
    eprintln!("Operation failed: {}", e);
}

Propagate Errors to UI

fn save_file(&mut self, cx: &mut Context<Self>) {
    cx.spawn(async move |this, cx| {
        match write_file(path, data).await {
            Ok(()) => {
                this.update(&mut *cx, |view, cx| {
                    view.status = "Saved successfully".into();
                    cx.notify();
                })?;
            }
            Err(e) => {
                this.update(&mut *cx, |view, cx| {
                    view.error = Some(format!("Save failed: {}", e));
                    cx.notify();
                })?;
            }
        }
        
        Ok(())
    }).detach_and_log_err(cx);
}

Variable Naming

Use Full Words

Rule: Avoid abbreviations, use descriptive names

// ❌ WRONG
let q = VecDeque::new();
let cnt = 0;
let btn = Button::new();

// ✅ CORRECT
let queue = VecDeque::new();
let count = 0;
let button = Button::new();

Meaningful Names

// ❌ WRONG
let x = calculate();
let temp = process(data);
let thing = Entity::new();

// ✅ CORRECT
let result = calculate();
let processed_data = process(data);
let user_profile = Entity::new();

Async Context Variable Shadowing

Use variable shadowing to scope clones in async contexts:

// ✅ CORRECT - clear scoping
fn start_work(&mut self, cx: &mut Context<Self>) {
    let data = self.data.clone();
    let config = self.config.clone();
    
    cx.spawn(async move |this, cx| {
        let result = process(data, config).await;
        
        this.update(&mut *cx, |view, cx| {
            view.result = result;
            cx.notify();
        })?;
        
        Ok(())
    }).detach();
}

File Organization

Avoid mod.rs Files

Rule: Use src/module.rs instead of src/module/mod.rs

// ❌ WRONG
src/
  components/
    mod.rs      # Don't do this
    button.rs

// ✅ CORRECT
src/
  components.rs  # Module file
  components/
    button.rs

Library Root Paths

For crates, specify library root in Cargo.toml:

[lib]
path = "src/my_lib.rs"  # Instead of default lib.rs

State Management

Call cx.notify() After Changes

// ❌ WRONG
fn update_data(&mut self, data: String, cx: &mut Context<Self>) {
    self.data = data;
    // Missing cx.notify() - UI won't update!
}

// ✅ CORRECT
fn update_data(&mut self, data: String, cx: &mut Context<Self>) {
    self.data = data;
    cx.notify(); // Trigger re-render
}

Use WeakEntity for Back-References

// ❌ WRONG - memory leak
struct Child {
    parent: Entity<Parent>, // Strong reference creates cycle!
}

// ✅ CORRECT
struct Child {
    parent: WeakEntity<Parent>, // Weak reference prevents leak
}

Rendering

Keep Render Pure

Rule: Don't mutate state in render() method

// ❌ WRONG
impl Render for MyView {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        self.render_count += 1; // Don't mutate in render!
        div().child(format!("Renders: {}", self.render_count))
    }
}

// ✅ CORRECT - mutate in event handlers
impl Render for MyView {
    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        div()
            .child(format!("Count: {}", self.count))
            .child(
                div()
                    .child("Increment")
                    .on_click(cx.listener(|this, _event, _window, cx| {
                        this.count += 1;
                        cx.notify();
                    }))
            )
    }
}

Use SharedString for Text

// ❌ LESS EFFICIENT
struct MyView {
    title: String,
}

// ✅ MORE EFFICIENT
struct MyView {
    title: SharedString,
}

Async Patterns

Detach or Store Tasks

// ❌ WRONG - task dropped immediately
cx.spawn(async move |this, cx| {
    // Work...
    Ok(())
});

// ✅ CORRECT - detach
cx.spawn(async move |this, cx| {
    // Work...
    Ok(())
}).detach();

// ✅ ALSO CORRECT - store for cancellation
self.current_task = Some(cx.spawn(async move |this, cx| {
    // Work...
    Ok(())
}));

Use background_spawn for CPU Work

// ❌ WRONG - blocks UI thread
cx.spawn(async move |this, cx| {
    let result = expensive_computation(); // Blocks UI!
    Ok(())
});

// ✅ CORRECT - run on background thread
cx.spawn(async move |this, cx| {
    let result = cx.background_spawn(async {
        expensive_computation()
    }).await;
    
    this.update(&mut *cx, |view, cx| {
        view.result = result;
        cx.notify();
    })?;
    
    Ok(())
});

Comments

Only Explain "Why"

Rule: Don't write comments that summarize code

// ❌ WRONG - obvious from code
// Increment the counter
self.counter += 1;

// Set the title to "Hello"
self.title = "Hello".into();

// ✅ CORRECT - explains non-obvious reasoning
// We must update the cache before notifying observers
// to ensure they see the most recent data
self.update_cache();
cx.notify();

// ✅ ALSO CORRECT - explains tricky logic
// Use saturating_sub to avoid underflow when count is 0
self.count = self.count.saturating_sub(1);

Testing

Use GPUI Timers in Tests

// ❌ WRONG
#[gpui::test]
async fn test_delay(cx: &mut TestAppContext) {
    smol::Timer::after(Duration::from_secs(1)).await;
}

// ✅ CORRECT
#[gpui::test]
async fn test_delay(cx: &mut TestAppContext) {
    cx.background_executor.timer(Duration::from_secs(1)).await;
    cx.background_executor.run_until_parked();
}

Build Guidelines

Use Project Scripts

# ❌ WRONG
cargo clippy

# ✅ CORRECT (for Zed-based projects)
./script/clippy

# Always use -q flag for cargo
cargo build -q
cargo test -q

Code Organization

Prefer Existing Files

Rule: Add functionality to existing files unless it's a new logical component

// Instead of creating many small files:
// src/button_click.rs
// src/button_hover.rs
// src/button_focus.rs

// Keep related functionality together:
// src/button.rs (with all button behavior)

Module Organization

// Good module structure
src/
  ui/
    components.rs   // Component definitions
    theme.rs        // Theme and colors
    styles.rs       // Shared styles
  data/
    models.rs       // Data models
    state.rs        // Application state

Summary of Best Practices

Rule	Rationale
Never use unwrap()	Prevents panics, forces explicit error handling
Never let _ = on fallible ops	Errors should be handled or logged
Use full variable names	Improves readability and maintainability
Avoid mod.rs files	Cleaner project structure
Call cx.notify() after mutations	Ensures UI updates
Use WeakEntity for back-refs	Prevents memory leaks
Keep render() pure	Avoids race conditions
Use SharedString for text	Reduces allocations
Detach or store tasks	Prevents cancelled work
Use GPUI timers in tests	Prevents test failures
Only comment "why", not "what"	Reduces noise, focuses on reasoning
Propagate errors to UI	Provides user feedback
Use background_spawn() for CPU work	Keeps UI responsive

Checklist for Code Review

• [ ] No unwrap() calls
• [ ] No silently discarded errors (let _ = on fallible ops)
• [ ] cx.notify() called after state changes
• [ ] Tasks are detached or stored
• [ ] Weak references used for back-pointers
• [ ] SharedString used for text
• [ ] No mutations in render()
• [ ] Descriptive variable names
• [ ] Comments explain "why", not "what"
• [ ] GPUI timers used in tests
• [ ] Errors propagated to UI layer

References

• GPUI Documentation
• Zed GEMINI.md
• Rust API Guidelines