From d585537e4c7d44deb489c98307d67ec99e56b5f3 Mon Sep 17 00:00:00 2001 From: jedarden Date: Sat, 23 May 2026 16:43:49 -0400 Subject: [PATCH] docs(pdftract-1x2): add verification note Documents implementation, test results, and retrospective for Phase 7.1.1. Co-Authored-By: Claude Code --- notes/pdftract-1x2.md | 92 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 92 insertions(+) create mode 100644 notes/pdftract-1x2.md diff --git a/notes/pdftract-1x2.md b/notes/pdftract-1x2.md new file mode 100644 index 0000000..c16d238 --- /dev/null +++ b/notes/pdftract-1x2.md @@ -0,0 +1,92 @@ +# pdftract-1x2: StructTree depth-first walker + /RoleMap resolution + +## Summary + +Implemented the depth-first walker over the PDF structure tree (/StructTreeRoot) with complete /RoleMap resolution support. This is Phase 7.1.1 of the plan. + +## Implementation + +### Files Modified/Created +- `crates/pdftract-core/src/parser/struct_tree.rs` (new, 1215 lines) +- `crates/pdftract-core/src/parser/mod.rs` (added exports) + +### Core Types +- `StructureType`: Enum covering all 40+ PDF 1.7 standard structure types (Document, Part, Art, Sect, Div, P, H1..H6, Table, Figure, etc.) +- `Kid`: Enum for /K array entries (Element, Mcid, Mcr, ObjRef) +- `StructElemNode`: Tree node with resolved type, inherited lang/actual_text, and children +- `StructTreeRoot`: Root container with kids array and RoleMap +- `RoleMap`: Mapping from non-standard to standard types with chain resolution + +### Key Features +1. **Depth-first traversal** via /K array handling all four entry types: + - StructElem dictionary (recursive) + - Integer MCID (direct marked content reference) + - MCR dictionary (marked content reference with explicit page) + - OBJR dictionary (annotation/XObject reference) + +2. **RoleMap resolution** with: + - Chain following (A -> B -> H1) + - Cycle detection (A -> B -> A → NonStruct with diagnostic) + - Standard type detection (no lookup needed for "P", "H1", etc.) + +3. **Attribute inheritance**: + - /Lang inherits from parent if not present on node + - /ActualText inherits from parent (overrides all descendant glyph text) + - /Alt (alternative text) extracted per-node + - /ID, /T, /E, /Pg also extracted + +## Verification + +### Unit Tests (17 tests, all PASS) +``` +test parser::struct_tree::tests::test_structure_type_from_name ... ok +test parser::struct_tree::tests::test_structure_type_is_heading ... ok +test parser::struct_tree::tests::test_structure_type_heading_level ... ok +test parser::struct_tree::tests::test_role_map_parse ... ok +test parser::struct_tree::tests::test_role_map_resolve ... ok +test parser::struct_tree::tests::test_role_map_chaining ... ok +test parser::struct_tree::tests::test_role_map_cycle_detection ... ok +test parser::struct_tree::tests::test_role_map_self_mapping ... ok +test parser::struct_tree::tests::test_struct_elem_node_new ... ok +test parser::struct_tree::tests::test_struct_tree_root_new ... ok +test parser::struct_tree::tests::test_struct_tree_root_default ... ok +test parser::struct_tree::tests::test_struct_tree_word_rolemap_integration ... ok +test parser::struct_tree::tests::test_struct_tree_lang_inheritance ... ok +test parser::struct_tree::tests::test_struct_tree_actual_text_scope ... ok +test parser::struct_tree::tests::test_struct_tree_mcr_kid ... ok +test parser::struct_tree::tests::test_struct_tree_objr_kid ... ok +test parser::struct_tree::tests::test_struct_tree_mcid_kid ... ok +``` + +### Acceptance Criteria Status +- ✓ Walker handles all four /K element kinds (Element, MCID, MCR, OBJR) without crashing +- ✓ /RoleMap chains resolve to a standard type or NonStruct +- ✓ /Lang and /ActualText inherit correctly down the tree +- ✓ Unit tests: fixtures with Word RoleMap (Heading1 -> H1) +- ✓ Unit tests: nested /Lang, /ActualText scope +- ✓ Public type StructElemNode is documented in the core crate + +## Commit +- Commit: `d41d47d` +- Message: `feat(pdftract-1x2): implement StructTree depth-first walker with RoleMap resolution` + +## Retrospective + +### What worked +- The implementation followed the PDF 1.7 spec closely, with clear separation between parsing and type resolution +- Test-driven approach worked well - each kid type, RoleMap feature, and inheritance pattern has dedicated tests +- Using `indexmap::IndexMap` for RoleMap preserves insertion order while providing O(1) lookups + +### What didn't +- Initial compilation error: mismatched types in match arms when resolving RoleMap references. Fixed by restructuring the error handling to assign to `root.role_map` directly rather than trying to return `RoleMap::new()` from a `PdfObject`-returning match. + +### Surprise +- The RoleMap can map to another non-standard name (chains), not directly to standard types. This required recursive resolution with cycle detection. + +### Reusable pattern +- For recursive type resolution through a mapping: track visited keys in a HashSet, emit diagnostic on cycle, return a safe fallback type. +- For inheritance in tree walkers: pass inherited values as `Option<&str>` to recursive calls, use `node.lang = lang.or_else(|| parent_lang.map(|s| s.to_string()))` to prefer local over inherited. + +## References +- Plan section 7.1 StructTree Exploitation (lines 2547-2549, 2552-2553) +- PDF 1.7 spec §14.7.4 (Structure Tree) and §14.8.4 (Standard Structure Types)