Sync macOS scroll containers with the engine

[dogukani]

Problem

On macOS, NSScrollView owns a scroll container's position but never reported it to the engine. Tree::scrollTop stayed 0, so:

• a VirtualList kept its first row window, and rows past #16 were blank;
• scroll listeners never fired, because Tree::setScrollTop is what dispatches them.

Change

• GeaFlippedClipView commits each settled bounds change with Tree::setScrollTop, as the iOS container does. It does not commit while rubber-banding. A change made during sync is committed after the walk.
• Children of a scroll container are placed in document space (node.layout.y - scrollTop), as on iOS, so they are not offset twice.

Verification

• targets/macos/test/native-scroll-commit.test.mjs pins the wiring. npm test passes (14 files).
• A local check (not part of this PR) scrolled the virtual-list example through the clip view programmatically:
  • Before this change, treeScrollTop=0 and rows Sync macOS scroll containers with the engine #1–#16 were shown.
  • After it, treeScrollTop matched y = 2140, 214000, 534498 and 0, and the matching rows were shown.
• Manual trackpad test: rows past #16 appear and update during movement, and the top returns to Sync macOS scroll containers with the engine #1. Captured frames showed no blank or mismatched rows.
• Tic Tac Toe builds and passes GEA_MACOS_VERIFY_ONCE.
• No iOS files changed. The iOS simulator run of the same example passed separately.

Related

An always-shown (legacy) scroller hides the right edge of scroll-container content and lets it scroll sideways, and the scroller knob cannot be dragged. Both happen on main as well. #2 addresses them.

Dependencies

macOS Virtual List scrolling needs this PR and geastack/core#57, geastack/compiler#1 and geastack/examples#1, which are merged. The example only refreshes its rows on the scroll event those PRs add.

Not covered

• overflow: scroll Views use the same path but were not exercised separately.

Summary by CodeRabbit

• Bug Fixes
  • macOS scroll views now keep the document’s scroll position in sync with valid native scroll offsets. Overscrolled offsets are excluded, and changes made during renderer updates are applied afterward.
  • Scrolled content now uses the document’s current scroll position when determining its placement, keeping content aligned as the view moves.

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• packages/geastack-apple/targets/macos/main/macos_renderer.mm

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📝 Walkthrough

Walkthrough

The macOS renderer now commits valid AppKit scroll offsets to tree state. It defers commits during renderer sync and uses scrollTop to position scroll-view children.

Changes

macOS Scroll Synchronization

Layer / File(s)	Summary
Native scroll state and layout packages/geastack-apple/targets/macos/main/macos_renderer.mm, packages/geastack-apple/targets/macos/test/native-scroll-commit.test.mjs	The clip view commits valid offsets to its tree node and defers commits during renderer sync. The renderer positions scroll-view children using scrollTop. The source-level test checks these behaviors and their wiring.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

Suggested reviewers: dashersw

Merge Risk: ⚪ Minimal · up to 86640

No actionable merge-blocking issue is established by the available evidence. The previously reported content-clipping concern does not apply at the reviewed head.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 86640

The change follows the existing native-scroll pattern and includes bounds and node checks. A deferred update may still outlive its scroll view’s ownership, and runtime behavior is not fully verified. No security finding was established.

Retained concerns

• Low · reliability · inferred: A scroll commit queued during sync can run after its clip view is removed. It checks that the stored node ID is in range, but not that the view still owns that node, so stale state propagation remains possible.

Security review details

Security Blast Radius

• inferred — A native scroll update can reach tree scroll state, scroll listeners, and scroll-dependent layout within the affected renderer. No cross-service dependency change is evidenced, but the full consumer set is unknown.

Trust Boundaries and Controls

• observed — The renderer supplies the clip view’s node ID. The clip view checks that ID and excludes rubber-band offsets before calling the shared tree setter.

Resilience and Maintainability Implications

• inferred — Deferral avoids changing tree scroll state mid-walk, but neither the queued callback nor teardown establishes that its node assignment remains current. Whether repeated commits are suppressed also depends on the unavailable Tree setter implementation.

Hardening Proposals

• proposed — Invalidate or revalidate node ownership when a clip view is detached, before a queued scroll commit can update tree state.

🚥 Pre-merge checks | ✅ 4 | ❌ 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%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: synchronizing macOS scroll-container positions with the engine.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files. (1 skipped: 1 unsupported.)

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✨ Finishing Touches

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Actionable comments posted: 1

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Inline comments:
In `@packages/geastack-apple/targets/macos/main/macos_renderer.mm`:
- Line 1585: Update the width calculation in applyScrollContentSize so a visible
legacy scroller cannot narrow the document below node.layout.width; preserve
engine-layout coordinates used by syncRecursive so right-aligned children remain
reachable.

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Configuration used: defaults

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📒 Files selected for processing (5)

• packages/geastack-apple/targets/macos/README.md
• packages/geastack-apple/targets/macos/main/macos_main.mm
• packages/geastack-apple/targets/macos/main/macos_renderer.h
• packages/geastack-apple/targets/macos/main/macos_renderer.mm
• packages/geastack-apple/targets/macos/test/native-scroll-commit.test.mjs

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