| name | cmux-debugging |
| description | Debug logging, Debug menu, runtime pitfalls, typing-latency-sensitive paths, SwiftUI list snapshot boundaries, OS-version repros, and local visual iteration for cmux. Use when adding debug probes, diagnosing UI/runtime issues, touching terminal rendering, tab/sidebar list views, drag/drop UTTypes, or using the Debug menu. |
cmux Debugging
Debug event log
Put debug event instrumentation (keys, mouse, focus, splits, tabs) in the unified DEBUG build log. This is not a requirement to log every new code path; most probes belong to a dogfood debug loop and are removed before merge.
tail -f "$(cat /tmp/cmux-last-debug-log-path 2>/dev/null || echo /tmp/cmux-debug.log)"
- Untagged Debug app logs to
/tmp/cmux-debug.log; tagged (./scripts/reload.sh --tag <tag>) to /tmp/cmux-debug-<tag>.log.
reload.sh writes the current log path to /tmp/cmux-last-debug-log-path and the selected dev CLI path to /tmp/cmux-last-cli-path, and points /tmp/cmux-cli and $HOME/.local/bin/cmux-dev at that CLI.- Implementation:
Packages/macOS/CMUXDebugLog/Sources/CMUXDebugLog/DebugEventLog.swift. App shim: Sources/App/DebugLogging.swift. Both are #if DEBUG, so every call site must be wrapped in #if DEBUG / #endif.
cmuxDebugLog("message") timestamps and appends in real time. A 500-entry ring buffer backs it; CMUXDebugLog.DebugEventLog.shared.dump() writes the full buffer to file.- Key events are logged in
AppDelegate.swift (monitor, performKeyEquivalent); mouse/UI events inline in views (ContentView, BrowserPanelView).
- Stable event prefixes:
focus.panel, focus.bonsplit, focus.firstResponder, focus.moveFocus, tab.select, tab.close, tab.dragStart, tab.drop, pane.focus, pane.drop, divider.dragStart.
Debug menu
DEBUG builds get a Debug menu in the macOS menu bar. When the user says "debug menu" or "debug window" they mean this, not defaults write.
Debug > Debug Windows holds panels for tuning layout, colors, and behavior, listed alphabetically with no dividers. To add one: create an NSWindowController subclass with a shared singleton, register it in the "Debug Windows" menu in Sources/cmuxApp.swift, and back it with a SwiftUI view using @AppStorage bindings for live changes.
Runtime pitfalls
- Custom drag-and-drop UTTypes must be declared in
Resources/Info.plist under UTExportedTypeDeclarations.
- Do not add an app-level display link or manual
ghostty_surface_draw loop; rely on Ghostty wakeups/renderer to avoid typing lag.
WindowTerminalHostView.hitTest() in Sources/TerminalWindowPortal.swift runs on every event including keyboard. Add no work outside the isPointerEvent guard.TabItemView in Sources/ContentView.swift uses Equatable plus .equatable() to skip body re-evaluation during typing. Do not add environment/store/binding reads without updating == and keeping .equatable() at the call site.TerminalSurface.forceRefresh() in Sources/GhosttyTerminalView.swift runs on every keystroke. No allocations, file I/O, or formatting.SurfaceSearchOverlay must be mounted from GhosttySurfaceScrollView in Sources/GhosttyTerminalView.swift, not from SwiftUI panel containers.- Views below a
LazyVStack / LazyHStack / List / ForEach boundary receive immutable snapshots plus closures, never an observable store.
- Functions called from SwiftUI
body must not mutate state or schedule store writes.
- Foundation, SwiftUI, AttributeGraph, and WebKit semantics change between macOS majors. Test on the reporter's macOS before declaring a user repro disproven.
Detailed references
