Don'ts

The hard list, with the nd check rule that fires for each.

The hard list. Each line says what to do instead and, where nd check enforces it, the rule id that fires. Silence a finding only with a reason: put // nd-allow(rule-id): why on the line or the line above.

Structure

• Don't draw a replica of a sidebar, toolbar, traffic light, caption button, sheet, menu, alert, or system control. Use scaffold, toolbar, sidebar, source_list, titlebar, window_controls, window.open_sheet, .context_menu, window.alert, or glass. (patterns.md)
• Don't put .drawn() on a structural element to change its look. Anywhere else, it needs a comment that says why the native control can't do the job. (drawn-reason)
• Don't pad content past the window controls by hand. For a custom titlebar, use titlebar(), which reserves the controls' inset on every OS.
• Don't branch on the OS in view code. Use intents, the .on_macos(..) family, or nd::platform::has(Feature::..). (cfg-target-os)
• Don't name gpui or objc2 outside a native widget module. (framework-internals)

Looks

• Don't write a color, radius, spacing, or font size literal in a view. Read cx.theme(). Color constructors live only in src/theme.rs. (colour-literal, and the appearance audit)
• Don't add a window without adding it to tests/appearance.rs.
• Don't fake glass with a translucent fill. Use glass(). (styling.md)
• Don't inline SVG. Use Icon. (inline-svg)

Behavior

• Don't feed a scroll container with .children(..) for anything that can grow past 50 rows. Use list, table, grid, or tree over a keyed ListState. (scroll-list, widgets.md)
• Don't key list rows by index, and don't rebuild the item list to force a refresh. Bump the row's version with set_items_versioned.
• Don't build popups from absolutely positioned divs or GPUI's deferred/anchored. Use popover, panel, tooltip, .context_menu, or a built-in. (floating-element)
• Don't guard controlled values with "ignore the next change" flags. Store what the event says and render it back. To refuse a change, don't store it.
• Don't call app code from a native callback. Emit through Emit, wrap setters in cx.programmatic(..), and keep one Synced<T> for each controlled prop.
• Don't use Instant::now, thread::sleep, or smol::Timer in UI code. Use the frame clock (window.now()) and nd::system::spawn. (clock-in-ui)
• Don't block the main thread on disk, network, or decoding.
• Don't use unwrap, expect, dbg!, todo!, or println! outside tests. Return errors, or report them with nd::report_issue(..). (clippy, denied by nd check)

Dependencies

• Don't edit the nd git tag or the [patch.crates-io] GPUI block in Cargo.toml by hand. nd upgrade moves both together. A mismatch builds two GPUIs or fails to resolve.

Testing and debugging

• Don't try to reproduce a bug before you read nd diagnose --last.
• Don't test in a real window what tier 1 can see. Tier 3 is for what only the OS does. (testing.md)
• Don't kill a tier 3 run that holds the machine lock, and don't delete the lock file. A queued run is waiting its turn.
• Don't sleep in tests. expect(..) and run_until_idle() wait for the condition.

Shell and files

• Don't run rm or mv on a variable path: rm -rf "$DIR/" with an empty DIR is rm -rf /. Delete only directories that your code created, through one helper that refuses empty paths and anything outside its root.
• Don't run pkill -f <pattern>. It matches other agents' processes. Stop what you started by its pid.
• Don't discard uncommitted work that you didn't write (git reset --hard, git checkout -- ., git stash, git clean). Another agent might be in the middle of an edit in the same tree.