pdftract/notes/pdftract-2yl9j.md

pdftract-2yl9j: Heading Detection Implementation Verification

Task

Implement classify_heading(block, page_body_median_font_size) -> bool for Phase 4.4 heading detection.

Status: ALREADY IMPLEMENTED ✓

The heading detection functionality is already fully implemented in:

• File: crates/pdftract-core/src/layout/line.rs
• Functions: classify_heading (lines 666-703) and classify_page_headings (lines 705-722)

Implementation Details

classify_heading Function

pub fn classify_heading<L>(block: &mut BlockInput<L>, page_body_median_font_size: f32) -> bool
where
    L: LineMetadata + Clone,
{
    // INV: threshold is strictly > 1.2
    let ratio = block.median_font_size / page_body_median_font_size;
    let size_criterion = ratio > 1.2;

    // Single-line criterion
    let line_count_criterion = block.lines.len() <= 1;

    if size_criterion && line_count_criterion {
        block.kind = "heading".to_string();
        true
    } else {
        false
    }
}

Implementation Correctness

All requirements met:

1. ✓ classify_heading(block, page_body_median_font_size) -> bool signature
2. ✓ Returns true when block.median_font_size > 1.2 * page_body_median
3. ✓ AND block.lines.len() <= 1
4. ✓ Sets block.kind = "heading" on positive

INV compliance:

• Threshold is strictly > 1.2, not >= 1.2 (line 692)

Acceptance Criteria Verification

All acceptance criteria tests exist and pass:

Test Case	Expected	Status
18pt block, body 12pt, 1 line	Heading (1.5 > 1.2)	✓ PASS
14pt block, body 12pt, 1 line	NOT (1.17 < 1.2)	✓ PASS
18pt block, 3 lines	NOT (too many lines)	✓ PASS
12pt block, body 12pt	NOT	✓ PASS

Additional Tests

• Threshold exactly 1.2: NOT heading (strict inequality) ✓
• Empty block (0 lines): NOT heading ✓
• 2-line block: NOT heading ✓

Test Results

Tests were run successfully with cargo nextest run:

PASS [   0.006s] ( 1/10) test_classify_heading_18pt_block_12pt_body_one_line_heading
PASS [   0.006s] ( 2/10) test_classify_heading_empty_lines_not_heading
PASS [   0.006s] ( 3/10) test_classify_heading_small_page_body_median
PASS [   0.006s] ( 4/10) test_classify_heading_18pt_block_three_lines_not_heading
PASS [   0.006s] ( 5/10) test_classify_heading_large_page_body_median
PASS [   0.006s] ( 6/10) test_classify_heading_14pt_block_12pt_body_one_line_not_heading
PASS [   0.006s] ( 7/10) test_classify_heading_threshold_exactly_1_2_not_heading
PASS [   0.006s] ( 8/10) test_classify_heading_12pt_block_12pt_body_not_heading
PASS [   0.006s] ( 9/10) test_classify_heading_two_lines_not_heading
PASS [   0.006s] (10/10) test_classify_heading_threshold_just_above_1_2_is_heading

Notes

• The implementation uses string kind field (set to "heading") following the same pattern as caption.rs
• There are pre-existing compilation errors in other files (header_footer.rs, table/output.rs) that prevent the full test suite from running, but these are unrelated to the heading detection implementation
• The heading detection code itself compiles correctly and all tests pass when run in isolation

Conclusion

The task is already complete. The classify_heading function is fully implemented, well-tested, and meets all acceptance criteria specified in the bead description and the plan (Phase 4.4, line 1702).