LibWeb: Derive node display facts from style payloads on demand

[kalenikaliaksandr]

Every style application re-derived four facts from the fresh computed values and stamped them into the arena NodeData record: the two table display classifications, a bitset of display predicates, and the own-style block-formatting-context flag. The stamps duplicated data the node's mirrored group payloads already carry, could drift from them if any write path forgot to restamp, and kept C++ copies of the block-formatting-context predicate and the table display classification alive purely to feed the mirror.

Tree building, formatting-context classification, and table grid construction now read these facts straight from the box group payload: StyleReader classifies the display value into FfiTableDisplay and evaluates the computed-style half of the block-formatting-context predicate, and styleless nodes answer every predicate with the same defaults the zeroed stamps used to produce. The mirror shrinks to storing the style pointer and the payload array, NodeData drops the three stamp bytes, and the NodeDisplayFlag enum, the OwnStyleEstablishesBlockFormattingContext flag, and the C++ predicate and classification helpers are deleted. The NodeData layout tests follow the new field offsets, and the stamp-based composite test for the block-formatting-context predicate goes away with the bits it exercised.

[coderabbitai]

📝 Walkthrough

Walkthrough

Layout display, table roles, positioning, containment, and block-formatting-context classification now use live Rust StyleReader values. Cached display fields and flags are removed from NodeData, while formatting contexts, layout state, tree building, and table fixup consume style-based accessors.

Changes

Style contracts and computed-style facts

Layer / File(s)	Summary
Node-data and style-reader contracts Libraries/LibWeb/Layout/Node.h, Libraries/LibWeb/Rust/build.rs, Libraries/LibWeb/Rust/src/layout/{mod.rs,node_data.rs,style_facts.rs}	Cached display fields and flags are removed from NodeData; StyleReader now exposes display, table, positioning, containment, and block-formatting-context facts.
Layout classification consumers Libraries/LibWeb/Rust/src/layout/{formatting_context.rs,layout_state.rs,node_facts.rs}	Formatting-context and layout predicates receive optional current and parent style readers and derive classification from computed style.
Tree-builder style integration Libraries/LibWeb/Rust/src/layout/tree_builder.rs	Tree-builder host accessors replace cached display checks across replacement, insertion, generated-content, first-letter, and child classification paths.
Table traversal and fixup Libraries/LibWeb/Rust/src/layout/{table_formatting_context.rs,tree_builder.rs}	Table traversal, wrapper generation, and misparented-table handling obtain table roles through style-aware accessors.

Estimated code review effort: 4 (Complex) | ~60 minutes

Sequence Diagram(s)

sequenceDiagram
  participant LayoutTreeBuilder
  participant TreeBuilderHost
  participant StyleReader
  participant TableFormattingContext
  LayoutTreeBuilder->>TreeBuilderHost: request node classification
  TreeBuilderHost->>StyleReader: read computed display values
  StyleReader-->>TreeBuilderHost: return display and table roles
  TreeBuilderHost-->>LayoutTreeBuilder: return classification
  TableFormattingContext->>TreeBuilderHost: request table_display(node)
  TreeBuilderHost-->>TableFormattingContext: return FfiTableDisplay

Loading

Possibly related PRs

• LadybirdBrowser/ladybird#10824: Introduces related FfiDisplay predicates used by the style-based classifications.
• LadybirdBrowser/ladybird#10838: Introduces the tree-builder architecture refined by this migration.
• LadybirdBrowser/ladybird#10870: Adds the cached display and table fields removed in this change.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description directly matches the changes by explaining the move from stamped NodeData display facts to on-demand StyleReader-derived values.
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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🧹 Nitpick comments (1)

Libraries/LibWeb/Rust/src/layout/layout_state.rs (1)

622-627: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Extract the triplicated "replaced-element table-display adjustment" predicate. The exact same condition — IsReplacedElement flag set and style.table_display_before() != FfiTableDisplay::Other — is independently implemented in three places. Consolidating into a single shared (data, style) free function (alongside node_is_out_of_flow/node_creates_block_formatting_context in node_facts.rs) would remove the risk of the three copies drifting apart.

• Libraries/LibWeb/Rust/src/layout/layout_state.rs#L622-L627: replace the body of has_replaced_element_table_display_adjustment with a call to the new shared helper.
• Libraries/LibWeb/Rust/src/layout/formatting_context.rs#L3098-L3100: call the shared helper instead of inlining the check in formatting_context_type_created_by_node_data.
• Libraries/LibWeb/Rust/src/layout/tree_builder.rs#L2123-L2128: replace node_has_replaced_element_table_display_adjustment's body with a call to the shared helper (or delete it in favor of calling the helper directly at call sites).

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@Libraries/LibWeb/Rust/src/layout/layout_state.rs` around lines 622 - 627,
Extract the shared replaced-element table-display adjustment predicate into a
free function in node_facts.rs alongside node_is_out_of_flow and
node_creates_block_formatting_context, accepting the node data and style and
checking IsReplacedElement plus table_display_before() !=
FfiTableDisplay::Other. Update
Libraries/LibWeb/Rust/src/layout/layout_state.rs:622-627,
Libraries/LibWeb/Rust/src/layout/formatting_context.rs:3098-3100, and
Libraries/LibWeb/Rust/src/layout/tree_builder.rs:2123-2128 to call the helper,
removing their duplicated checks while preserving existing APIs or deleting the
redundant wrapper where appropriate.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@Libraries/LibWeb/Rust/src/layout/layout_state.rs`:
- Around line 622-627: Extract the shared replaced-element table-display
adjustment predicate into a free function in node_facts.rs alongside
node_is_out_of_flow and node_creates_block_formatting_context, accepting the
node data and style and checking IsReplacedElement plus table_display_before()
!= FfiTableDisplay::Other. Update
Libraries/LibWeb/Rust/src/layout/layout_state.rs:622-627,
Libraries/LibWeb/Rust/src/layout/formatting_context.rs:3098-3100, and
Libraries/LibWeb/Rust/src/layout/tree_builder.rs:2123-2128 to call the helper,
removing their duplicated checks while preserving existing APIs or deleting the
redundant wrapper where appropriate.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: f570851b-91c3-4d1d-b684-83f64ba0fe63

📥 Commits

Reviewing files that changed from the base of the PR and between 2269ea5 and 7707e59.

📒 Files selected for processing (11)

• Libraries/LibWeb/Layout/Node.cpp
• Libraries/LibWeb/Layout/Node.h
• Libraries/LibWeb/Rust/build.rs
• Libraries/LibWeb/Rust/src/layout/formatting_context.rs
• Libraries/LibWeb/Rust/src/layout/layout_state.rs
• Libraries/LibWeb/Rust/src/layout/mod.rs
• Libraries/LibWeb/Rust/src/layout/node_data.rs
• Libraries/LibWeb/Rust/src/layout/node_facts.rs
• Libraries/LibWeb/Rust/src/layout/style_facts.rs
• Libraries/LibWeb/Rust/src/layout/table_formatting_context.rs
• Libraries/LibWeb/Rust/src/layout/tree_builder.rs

💤 Files with no reviewable changes (3)

• Libraries/LibWeb/Rust/build.rs
• Libraries/LibWeb/Rust/src/layout/mod.rs
• Libraries/LibWeb/Layout/Node.cpp