fix(organize): keep page labels on their pages when pages are deleted (fixes #2091) (#2093)

crates/organize/src/labels.rs

@@ -396,6 +396,31 @@ pub fn set_page_label_ranges(doc: &mut Document, ranges: &[LabelRange]) -> Resul
     Ok(())
 }
 
+/// After `deleted` pages (0-based, as they were numbered before the delete) are gone, move the label
+/// ranges with the pages they label: a range starts as many pages earlier as were deleted before
+/// it, and keeps its first number, so numbering continues over the gap as in Acrobat. A range whose
+/// first page went starts on the next page left; one left with no pages gives way to the next.
+/// A tree that can't be read is left as it is: the delete still goes ahead.
+pub(crate) fn drop_deleted_pages(doc: &mut Document, deleted: &[usize]) -> Result<(), OrganizeError> {
+    let Ok(old) = checked_ranges(doc) else { return Ok(()) };
+    let mut deleted = deleted.to_vec();
+    deleted.sort_unstable();
+    deleted.dedup();
+    let mut ranges: Vec<LabelRange> = Vec::with_capacity(old.len());
+    for r in &old {
+        let start = r.start.saturating_sub(deleted.partition_point(|d| *d < r.start));
+        match ranges.last_mut() {
+            // The later range is the one on the first page left; ranges stay sorted by start.
+            Some(last) if last.start == start => *last = LabelRange { start, ..r.clone() },
+            _ => ranges.push(LabelRange { start, ..r.clone() }),
+        }
+    }
+    if ranges == old {
+        return Ok(());
+    }
+    set_page_label_ranges(doc, &ranges)
+}
+
 /// Acrobat's "Number pages": label pages `from..=to` (0-based) with `style`, `prefix` and
 /// starting number `first`; pages after `to` keep the labels they had.
 pub fn number_pages(doc: &mut Document, from: usize, to: usize, style: LabelStyle, prefix: &str, first: u32) -> Result<(), OrganizeError> {

crates/organize/src/lib.rs

@@ -181,6 +181,7 @@ pub fn delete_pages(doc: &mut Document, indices: &[usize]) -> Result<(), Organiz
         return Err(OrganizeError::WouldRemoveAllPages);
     }
     rebuild(doc, &keep)?;
+    labels::drop_deleted_pages(doc, indices)?;
     // The deleted pages go for good: bookmarks, links and widgets that still point at one would
     // otherwise keep it, with its content, in the saved file. Their form widgets leave the form,
     // and bookmarks and links that went to them lose that destination.

crates/organize/src/tests.rs

@@ -1472,6 +1472,38 @@ fn number_pages_like_acrobat() {
     assert!(d.get(d.root().unwrap()).as_dict().unwrap().get(b"PageLabels").is_none());
 }
 
+/// Deleting pages moves the label ranges with the pages they label (#2091): later ranges start that
+/// many pages earlier and keep numbering on, a range whose first page went starts on the next page
+/// left, and a range left with no pages gives way to the one after it.
+#[test]
+fn deleting_pages_keeps_the_label_ranges_on_their_pages() {
+    use crate::{LabelRange, LabelStyle::*};
+    let ten = || {
+        let mut d = doc_a();
+        for at in 3..10 {
+            crate::insert_blank_page(&mut d, at, 300.0, 400.0).unwrap();
+        }
+        let ranges = [
+            LabelRange { start: 0, style: LowerRoman, prefix: String::new(), first: 1 },
+            LabelRange { start: 3, style: Decimal, prefix: String::new(), first: 1 },
+            LabelRange { start: 7, style: Decimal, prefix: "A-".into(), first: 1 },
+        ];
+        crate::set_page_label_ranges(&mut d, &ranges).unwrap();
+        assert_eq!(crate::page_labels(&d).unwrap(), ["i", "ii", "iii", "1", "2", "3", "4", "A-1", "A-2", "A-3"]);
+        d
+    };
+    for (deleted, expected) in [
+        (&[4, 5][..], &["i", "ii", "iii", "1", "2", "A-1", "A-2", "A-3"][..]),
+        (&[3], &["i", "ii", "iii", "1", "2", "3", "A-1", "A-2", "A-3"]),
+        (&[3, 4, 5, 6], &["i", "ii", "iii", "A-1", "A-2", "A-3"]),
+    ] {
+        let mut d = ten();
+        crate::delete_pages(&mut d, deleted).unwrap();
+        assert_eq!(crate::page_labels(&d).unwrap(), expected, "after deleting {deleted:?}");
+        assert_eq!(crate::page_labels(&full_roundtrip(&d)).unwrap(), expected, "reopened after deleting {deleted:?}");
+    }
+}
+
 #[test]
 fn page_label_limits_reject_unsupported_edits_before_mutating() {
     use crate::LabelStyle::*;