LibWeb: Move anonymous text run filtering to Rust

[kalenikaliaksandr]

The flex and grid item collection paths crossed into C++ to identify anonymous boxes containing only untransformed ASCII whitespace after node topology and text content had moved into the Rust arena.

Record the pre-transform whitespace classification during existing text synchronization, evaluate the predicate directly from arena node data in Rust, and remove the formatting-context callback. The separate fact keeps TextNode::text() behavior when rendered text differs after transformation or first-letter slicing.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 4f9aee86-af1b-4fab-8538-03bec5a31667

📥 Commits

Reviewing files that changed from the base of the PR and between 1505e5e and e8f298d.

📒 Files selected for processing (6)

• Libraries/LibWeb/Layout/LayoutRustBridge.cpp
• Libraries/LibWeb/Layout/TextNode.cpp
• Libraries/LibWeb/Rust/src/layout/flex_formatting_context.rs
• Libraries/LibWeb/Rust/src/layout/formatting_context.rs
• Libraries/LibWeb/Rust/src/layout/grid_formatting_context.rs
• Libraries/LibWeb/Rust/src/layout/layout_node_arena.rs

💤 Files with no reviewable changes (1)

• Libraries/LibWeb/Layout/LayoutRustBridge.cpp

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📝 Walkthrough

Walkthrough

The change moves anonymous whitespace text-run detection into Rust. Text nodes now synchronize an ASCII-whitespace flag into the layout arena, and flex/grid formatting contexts use a Rust predicate instead of a C++ callback.

Changes

Anonymous text-run handling

Layer / File(s)	Summary
Text metadata synchronization Libraries/LibWeb/Layout/TextNode.cpp, Libraries/LibWeb/Rust/src/layout/layout_node_arena.rs	Text synchronization and arena storage now retain whether untransformed text is ASCII whitespace.
Rust-side skip predicate Libraries/LibWeb/Rust/src/layout/formatting_context.rs	Anonymous, non-generated nodes are eligible only when all child nodes are text containing ASCII whitespace.
Flex/grid integration and callback removal Libraries/LibWeb/Rust/src/layout/flex_formatting_context.rs, Libraries/LibWeb/Rust/src/layout/grid_formatting_context.rs, Libraries/LibWeb/Layout/LayoutRustBridge.cpp	Flex and grid call the Rust predicate directly, while the bridge callback and helper are removed.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant TextNode
  participant LayoutNodeArena
  participant FlexOrGridFormattingContext
  participant FfiLayoutFcCallbacks

  TextNode->>LayoutNodeArena: synchronize text and ASCII-whitespace flag
  FlexOrGridFormattingContext->>FfiLayoutFcCallbacks: check anonymous text run
  FfiLayoutFcCallbacks->>LayoutNodeArena: inspect node and child text metadata
  LayoutNodeArena-->>FfiLayoutFcCallbacks: return stored whitespace data
  FfiLayoutFcCallbacks-->>FlexOrGridFormattingContext: return skip decision

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Possibly related PRs

• LadybirdBrowser/ladybird#10870: Introduced the Rust-backed layout arena plumbing extended by this change.
• LadybirdBrowser/ladybird#10901: Related Rust layout-context callback and anonymous whitespace text-run handling changes.

Suggested reviewers: awesomekling, tcl3

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description accurately matches the changes: moving anonymous text-run filtering to Rust, recording ASCII-whitespace state, and removing the callback.
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.

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