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: // 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, glass. (patterns.md)
• Don't put .drawn() on a structural element to change its look. Anywhere else it needs a comment saying why the native control cannot do it. (drawn-reason)
• Don't pad content past the window controls by hand. A custom titlebar is titlebar(), which reserves their inset on every OS.
• Don't branch on the OS in view code. Use intents, .on_macos(..) and friends, 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 colour, radius, spacing or font size literal in a view. Read cx.theme(); colour constructors live in src/theme.rs only. (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)

Behaviour

• Don't feed a scroll container with .children(..) for anything that can pass 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; refuse a change by not storing it.
• Don't call app code from a native callback. Emit through Emit, wrap setters in cx.programmatic(..), keep a Synced<T> per 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 reproduce a bug before reading 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 rm or mv a variable path: rm -rf "$DIR/" with an empty DIR is rm -rf /. Delete only directories your code created, through one helper that refuses empty paths and anything outside its root.
• Don't pkill -f <pattern>. It matches other agents' processes. Stop what you started by pid.
• Don't discard uncommitted work you did not write (git reset --hard, git checkout -- ., git stash, git clean). Another agent may be mid-edit in the same tree.