M4: bookmarks from text styles need copying permission and keep columns apart (#1693)

CodeRabbit on #4560:
- The bookmark titles are the document's text, so the edit now needs
  copying permission as well as assembly, and Document::text_styles (the
  dialog's samples) is empty when copying is withheld; the automation
  text_styles tool already checked it.
- A heading went on to the next row whenever it was close below in the
  same style, so same-style headings in two columns on staggered rows ran
  together into one bookmark. A line continues a heading only when it lies
  under it.
- Lines found their style by a scan over every style so far; they are now
  indexed by font, weight, slant and quarter-point size, so a page with
  thousands of styles no longer makes the scan quadratic.

Regression tests for the first two (each fails without its fix).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LymhVaGZCWwB9HNEbLzeMM

crates/engine/src/lib.rs

@@ -622,7 +622,11 @@ impl Document {
 
     /// The styles the document's text is set in, the largest first, for bookmarks from text
     /// styles (#1693).
+    /// Empty when the document doesn't allow copying: the samples are its text.
     pub fn text_styles(&self) -> Vec<text_style_bookmarks::TextStyleUse> {
+        if !self.allows_copying() {
+            return Vec::new();
+        }
         self.editor.as_ref().map(|e| text_style_bookmarks::styles(&e.cos)).unwrap_or_default()
     }
 
@@ -2348,7 +2352,6 @@ fn check_permission(edit: &Edit, p: &pdfcraft_cos::Permissions) -> Result<(), Ed
         | Edit::SetBookmarkColor { .. }
         | Edit::SetBookmarkStyle { .. }
         | Edit::BookmarksFromStructure
-        | Edit::BookmarksFromTextStyles { .. }
         | Edit::NumberPages { .. } => {
             if p.assemble() {
                 Ok(())
@@ -2356,6 +2359,17 @@ fn check_permission(edit: &Edit, p: &pdfcraft_cos::Permissions) -> Result<(), Ed
                 Err(EditError::NotPermitted("page changes"))
             }
         }
+        // Creates bookmarks (assembly), and their titles are the document's text, copied out of it
+        // (Table 22, bit 5), as an export of it would be.
+        Edit::BookmarksFromTextStyles { .. } => {
+            if !p.assemble() {
+                Err(EditError::NotPermitted("page changes"))
+            } else if !p.copy() {
+                Err(EditError::NotPermitted("copying text and images"))
+            } else {
+                Ok(())
+            }
+        }
         Edit::AddMeasurement(_)
         | Edit::AddAnnotation(_)
         | Edit::AddCustomStamp { .. }

crates/engine/src/tests.rs

@@ -1924,6 +1924,52 @@ fn bookmarks_from_text_styles_nest_the_headings_and_undo() {
     assert!(s.get(id).unwrap().info.outline.is_empty());
 }
 
+/// CodeRabbit on #4560: bookmark titles from text styles are the document's text, so a document
+/// that forbids copying lists no styles and refuses the edit, as it refuses other extraction.
+#[test]
+fn bookmarks_from_text_styles_need_copying_permission() {
+    let mut doc = pdfcraft_cos::Document::open(Arc::new(styled_headings_fixture())).unwrap();
+    doc.set_encryption(&pdfcraft_cos::NewEncryption {
+        algorithm: pdfcraft_cos::Algorithm::Aes256,
+        user_password: "",
+        owner_password: "owner",
+        permissions: -1 ^ 0b1_0000,
+        encrypt_metadata: true,
+        seed: [7; 32],
+    })
+    .unwrap();
+    let bytes = Arc::new(pdfcraft_cos::write_full(&doc, &Default::default()).unwrap());
+    let mut s = Session::new();
+    let id = s.open("r.pdf", None, bytes.clone(), None).unwrap();
+    assert!(s.get(id).unwrap().allows_assembly() && !s.get(id).unwrap().allows_copying());
+    assert!(s.get(id).unwrap().text_styles().is_empty(), "no samples of text that may not be copied");
+    let style = text_style_bookmarks::TextStyle { font: "Helvetica-Bold".into(), size: 18.0, bold: true, italic: false };
+    let err = s.apply(id, Edit::BookmarksFromTextStyles { levels: vec![style.clone()] }).unwrap_err();
+    assert_eq!(err, EditError::NotPermitted("copying text and images"));
+    let owner = s.open("r.pdf", None, bytes, Some("owner")).unwrap();
+    assert!(!s.get(owner).unwrap().text_styles().is_empty());
+    assert!(s.apply(owner, Edit::BookmarksFromTextStyles { levels: vec![style] }).is_ok(), "the owner may");
+}
+
+/// CodeRabbit on #4560: two headings in one style in two columns, the right one a little lower,
+/// are two bookmarks, not one heading run on across the columns.
+#[test]
+fn headings_in_two_columns_are_two_bookmarks() {
+    let page = "BT /FB 14 Tf 72 700 Td (Left heading) Tj ET BT /FB 14 Tf 320 690 Td (Right heading) Tj ET";
+    let bytes = pdfcraft_testkit::Pdf::new()
+        .obj("<< /Type /Catalog /Pages 2 0 R >>")
+        .obj("<< /Type /Pages /Kids [3 0 R] /Count 1 /MediaBox [0 0 612 792] /Resources << /Font << /FB 5 0 R >> >> >>")
+        .obj("<< /Type /Page /Parent 2 0 R /Contents 4 0 R >>")
+        .stream("", page)
+        .obj("<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica-Bold /Encoding /WinAnsiEncoding >>")
+        .build();
+    let mut s = Session::new();
+    let id = s.open("cols.pdf", None, Arc::new(bytes), None).unwrap();
+    let style = s.get(id).unwrap().text_styles()[0].style.clone();
+    s.apply(id, Edit::BookmarksFromTextStyles { levels: vec![style] }).unwrap();
+    assert_eq!(outline_titles(&s.get(id).unwrap().info.outline), ["Untitled→0[Left heading→1,Right heading→1]"]);
+}
+
 /// `style` at another size.
 fn pdfcraft_engine_style(style: &text_style_bookmarks::TextStyle, size: f64) -> text_style_bookmarks::TextStyle {
     text_style_bookmarks::TextStyle { size, ..style.clone() }

crates/engine/src/text_style_bookmarks.rs

@@ -60,10 +60,11 @@ struct Line {
     page: usize,
     text: String,
     style: TextStyle,
-    /// Top, bottom and left of its box in user space.
+    /// Top, bottom, left and right of its box in user space.
     top: f64,
     bottom: f64,
     left: f64,
+    right: f64,
 }
 
 /// `name` without a subset tag: six capital letters and a `+` (ISO 32000-2 §9.9.2).
@@ -102,6 +103,7 @@ fn lines(doc: &Document) -> Vec<Line> {
                     top: y0.max(y1),
                     bottom: y0.min(y1),
                     left: x0.min(x1),
+                    right: x0.max(x1),
                 })
             })
             .collect();
@@ -117,8 +119,21 @@ fn lines(doc: &Document) -> Vec<Line> {
 /// are usually larger than the text around them.
 pub fn styles(doc: &Document) -> Vec<TextStyleUse> {
     let mut uses: Vec<(TextStyleUse, Option<usize>)> = Vec::new();
+    // The styles by font, weight, slant and size in quarter points, so a line is matched against
+    // the few styles near its size rather than every style found (a page can hold thousands).
+    // A size matches within a quarter point: the bucket's neighbours are looked at too.
+    let mut index: std::collections::HashMap<(String, bool, bool, i64), Vec<usize>> = std::collections::HashMap::new();
+    let bucket = |size: f64| (size / SIZE_TOLERANCE).floor() as i64;
     for line in lines(doc) {
-        match uses.iter_mut().find(|(u, _)| u.style.matches(&line.style)) {
+        let key = |b: i64| (line.style.font.clone(), line.style.bold, line.style.italic, b);
+        let b = bucket(line.style.size);
+        let found = [b.saturating_sub(1), b, b.saturating_add(1)]
+            .into_iter()
+            .filter_map(|b| index.get(&key(b)))
+            .flatten()
+            .copied()
+            .find(|&i| uses.get(i).is_some_and(|(u, _)| u.style.matches(&line.style)));
+        match found.and_then(|i| uses.get_mut(i)) {
             Some((u, last_page)) => {
                 u.lines = u.lines.saturating_add(1);
                 if *last_page != Some(line.page) {
@@ -128,6 +143,7 @@ pub fn styles(doc: &Document) -> Vec<TextStyleUse> {
             }
             None => {
                 let sample = line.text.chars().take(SAMPLE_CHARS).collect();
+                index.entry(key(b)).or_default().push(uses.len());
                 uses.push((TextStyleUse { style: line.style, lines: 1, pages: 1, sample }, Some(line.page)));
             }
         }
@@ -144,19 +160,21 @@ pub fn styles(doc: &Document) -> Vec<TextStyleUse> {
 /// is one bookmark. Each goes to the top of its heading.
 pub fn headings(doc: &Document, levels: &[TextStyle]) -> Vec<OutlineEntry> {
     let mut entries: Vec<OutlineEntry> = Vec::new();
-    // The heading the previous line belonged to: its level, and the top and bottom of its last
-    // line.
-    let mut open: Option<(usize, f64, f64)> = None;
+    // The heading the previous line belonged to: its level, and the top, bottom, left and right
+    // of its last line.
+    let mut open: Option<(usize, f64, f64, f64, f64)> = None;
     for line in lines(doc) {
         let Some(level) = levels.iter().position(|s| s.matches(&line.style)) else {
             open = None;
             continue;
         };
-        // A heading goes on to the next row down, close below its last line. A line on the same
-        // row (two headings side by side) is a heading of its own.
-        let continues = open.is_some_and(|(l, top, bottom)| {
+        // A heading goes on to the next row down, close below its last line and under it. A line
+        // on the same row (two headings side by side), or in another column, is a heading of
+        // its own.
+        let continues = open.is_some_and(|(l, top, bottom, left, right)| {
             let size = line.style.size;
-            l == level && line.top < top - size * 0.5 && bottom - line.top < size * 0.6
+            let under = line.left < right && left < line.right;
+            l == level && line.top < top - size * 0.5 && bottom - line.top < size * 0.6 && under
         }) && entries.last().is_some_and(|e| e.page == line.page);
         if continues {
             if let Some(e) = entries.last_mut()
@@ -181,7 +199,7 @@ pub fn headings(doc: &Document, levels: &[TextStyle]) -> Vec<OutlineEntry> {
                 top: Some(line.top),
             });
         }
-        open = Some((level, line.top, line.bottom));
+        open = Some((level, line.top, line.bottom, line.left, line.right));
     }
     entries
 }