Reduce typing lag by hiding invisible views from accessibility tree by lawrencecchen · Pull Request #862 · manaflow-ai/cmux

lawrencecchen · 2026-03-04T10:26:02Z

Summary

Profiling cmux NIGHTLY with sample shows the main thread spending ~24% of CPU time in AccessibilityViewGraph.needsUpdate during every SwiftUI layout pass. The accessibility subsystem walks the entire view tree, including invisible views (opacity-0, hit-testing disabled), blocking the run loop from dequeuing key events and causing typing lag.

Hide inactive workspaces from accessibility (ContentView.swift). All mounted workspaces sit in a ZStack; inactive ones are opacity-0 but still walked. Adding .accessibilityHidden(!isVisible) eliminates them from the walk.
Hide the tabs/notifications containers from accessibility when not selected.
Mark GhosttyTerminalView's HostContainerView as non-accessible. This empty NSView placeholder (portal pattern) has no content since the terminal surface lives in the AppKit layer above SwiftUI.

Note: NotificationsPage is effectively dead code for users (all notification paths go to the popover). Could be removed entirely in a follow-up.

Testing

Built successfully in Debug configuration.
Profile with sample <pid> 10 while typing to compare AccessibilityViewGraph.needsUpdate sample counts before/after.

Profiling data (before)

Main thread sample breakdown (10s capture, 5707 samples):

Samples	%	What
3576	63%	`NSHostingView.layout()` → SwiftUI view graph render
1381	24%	`AccessibilityViewGraph.needsUpdate`
1287	23%	SwiftUI accessibility `UpdateStack::update()`
514	9%	`AccessibilityViewModifierAccessor`

Summary by cubic

Hide invisible SwiftUI views from the accessibility tree to reduce layout overhead and improve typing responsiveness. This cuts time spent in AccessibilityViewGraph.needsUpdate during layout.

Performance
- Add .accessibilityHidden(!isVisible) for inactive workspaces in ContentView.
- Hide tabs and NotificationsPage from accessibility when not selected.
- Mark GhosttyTerminalView’s HostContainerView as non-accessible (role .none, element false).

^{Written for commit 5742799. Summary will update on new commits.}

Summary by CodeRabbit

Bug Fixes
- Improved screen reader and accessibility tool behavior by preventing them from traversing inactive UI sections, including hidden workspaces, non-selected notifications, and terminal placeholders. Users relying on assistive technologies will now experience more streamlined navigation.

Profiling shows the main thread spends ~24% of time in AccessibilityViewGraph.needsUpdate walking invisible SwiftUI views during every layout pass, blocking key event dequeue. - Add .accessibilityHidden on inactive workspaces in the ZStack (opacity-0 but still walked by the accessibility subsystem) - Add .accessibilityHidden on NotificationsPage and the tabs container when their respective selection is not active - Mark GhosttyTerminalView's HostContainerView (empty portal placeholder) as non-accessible since the terminal surface lives in the AppKit portal layer above SwiftUI

vercel · 2026-03-04T10:26:08Z

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Mar 4, 2026 10:26am

coderabbitai · 2026-03-04T10:26:35Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 0c16abe0-b55e-42be-b146-0a514c0b14ee

📥 Commits

Reviewing files that changed from the base of the PR and between f5de515 and 5742799.

📒 Files selected for processing (2)

Sources/ContentView.swift
Sources/GhosttyTerminalView.swift

📝 Walkthrough

Walkthrough

This pull request enhances accessibility by adding modifiers to hide non-visible or non-selected UI elements from assistive technologies. Additionally, a temporary container in the terminal view is marked to prevent accessibility traversal into placeholder elements.

Changes

Cohort / File(s)	Summary
Accessibility Visibility Controls `Sources/ContentView.swift`	Added `accessibilityHidden()` modifiers to workspaces, notifications, and tab views to hide UI elements from assistive technologies when they are not visually active or selected.
Terminal View Accessibility Guards `Sources/GhosttyTerminalView.swift`	Set accessibility role to none and disabled accessibility element status on temporary container to prevent assistive technology traversal into placeholder content.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 Hop along, the path is clear,
Accessibility blooms far and near,
Hidden elements stay out of sight,
Assistive tech sees only what's right!
A rabbit's code, precise and bright. ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main objective of the PR: reducing typing lag by hiding invisible views from the accessibility tree through strategic use of accessibilityHidden() modifiers.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings (stacked PR)
📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment
Commit unit tests in branch task-fix-accessibility-tree-typing-lag

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cubic-dev-ai

No issues found across 2 files

greptile-apps · 2026-03-04T10:28:14Z

Greptile Summary

This PR addresses typing lag caused by SwiftUI's accessibility subsystem walking the entire view tree during layout passes. The changes hide invisible views from the accessibility tree using .accessibilityHidden() modifiers, which should reduce CPU time spent in AccessibilityViewGraph.needsUpdate from ~24% to significantly less.

Key changes:

Inactive workspaces (opacity 0) are now hidden from accessibility tree
Tabs and notifications containers are hidden when not selected
HostContainerView placeholder is marked as non-accessible

The boolean logic correctly mirrors existing visibility patterns (opacity + hit testing), and follows the established pattern in the codebase of hiding invisible UI elements from accessibility. No actual accessibility functionality is affected since these views are already invisible to users.

Confidence Score: 5/5

This PR is safe to merge with no risk
The changes are minimal, logically correct, and follow existing patterns in the codebase. The accessibility modifiers only hide views that are already invisible, so there's no impact on actual accessibility functionality. The performance improvement is well-documented with profiling data.
No files require special attention

Important Files Changed

Filename	Overview
Sources/ContentView.swift	Added `.accessibilityHidden()` modifiers to workspace views, tabs, and notifications containers that are already invisible via opacity/selection state
Sources/GhosttyTerminalView.swift	Marked `HostContainerView` as non-accessible since it's an empty placeholder for the AppKit portal pattern

_{Last reviewed commit: 5742799}

…anaflow-ai#862)

…anaflow-ai#862) Profiling shows the main thread spends ~24% of time in AccessibilityViewGraph.needsUpdate walking invisible SwiftUI views during every layout pass, blocking key event dequeue. - Add .accessibilityHidden on inactive workspaces in the ZStack (opacity-0 but still walked by the accessibility subsystem) - Add .accessibilityHidden on NotificationsPage and the tabs container when their respective selection is not active - Mark GhosttyTerminalView's HostContainerView (empty portal placeholder) as non-accessible since the terminal surface lives in the AppKit portal layer above SwiftUI

vercel Bot deployed to Preview March 4, 2026 10:26 View deployment

cubic-dev-ai Bot reviewed Mar 4, 2026

View reviewed changes

lawrencecchen merged commit 102931d into main Mar 4, 2026
13 checks passed

coderabbitai Bot mentioned this pull request Mar 5, 2026

Fix split zoom visibility sync to prevent black browser pane #929

Closed

0xble added a commit to 0xble/cmux that referenced this pull request Mar 7, 2026

Reduce typing lag by hiding invisible views from accessibility tree (m…

bd8ea6a

…anaflow-ai#862)

This was referenced Mar 9, 2026

Shared tabs across windows #1090

Closed

Add minimal sidebar detail toggles #1312

Merged

Fix accessibility role on GhosttyScrollView for voice input tools #1441

Closed

This was referenced Mar 16, 2026

Hide workspace titlebar chrome in minimal mode #1479

Merged

fix(ui): immediately hide portal views when switching workspaces #1687

Closed

TerryChengTW mentioned this pull request Apr 2, 2026

[question] app_prefers_ocr blocklist — is the assumption still valid for Ghostty/iTerm2 on macOS? screenpipe/screenpipe#2685

Closed

coderabbitai Bot mentioned this pull request May 14, 2026

Fix keyboard accessibility for sidebar and titlebar controls #4181

Open

MechanicMishap mentioned this pull request Jun 10, 2026

Malformed AXHelpTag published in the accessibility window list (returns errors for AXSubrole/AXTitle) #5805

Open

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Reduce typing lag by hiding invisible views from accessibility tree - #862

Reduce typing lag by hiding invisible views from accessibility tree#862
lawrencecchen merged 1 commit into
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task-fix-accessibility-tree-typing-lag

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greptile-apps Bot commented Mar 4, 2026

Greptile Summary

Confidence Score: 5/5

Important Files Changed

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