M6: a custom stamp's line fills in the template's placeholders only (#1741)

Review on #2345 (gabglus): the line was filled by chained replaces, so a
placeholder inside the author's name ("Ada {date}") was filled in too.
stamp_line now walks the template once and expands only the {name},
{date} and {time} it finds there; the author's text is kept as written.
Trimming and the MAX_STAMP_LINE cut are unchanged. The loop advances by
whole characters (strip_prefix, or get() past the next char), so it
cannot panic.

stamp_lines_fill_in_the_name_date_and_time gains the review's case and
a name made only of a placeholder; both fail with the chained replaces.
The UI test checks the saved /PCByLine has no placeholder left (from
gabglus's commit f6760b37).

Co-Authored-By: gabglus <gabglus@hotmail.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/session/view.rs

@@ -74,7 +74,25 @@ impl Session {
     /// stamps' "By" line has them. Cut to [`MAX_STAMP_LINE`](crate::MAX_STAMP_LINE) characters.
     pub fn stamp_line(&self, template: &str, author: &str) -> String {
         let (date, time) = self.stamp_date_time();
-        let filled = template.trim().replace("{name}", author.trim()).replace("{date}", &date).replace("{time}", &time);
+        // One pass over the template, so a placeholder the author's name happens to contain
+        // (`Ada {date}`) stays as written rather than being filled in too.
+        let mut filled = String::new();
+        let mut rest = template.trim();
+        while let Some(c) = rest.chars().next() {
+            if let Some(after) = rest.strip_prefix("{name}") {
+                filled.push_str(author.trim());
+                rest = after;
+            } else if let Some(after) = rest.strip_prefix("{date}") {
+                filled.push_str(&date);
+                rest = after;
+            } else if let Some(after) = rest.strip_prefix("{time}") {
+                filled.push_str(&time);
+                rest = after;
+            } else {
+                filled.push(c);
+                rest = rest.get(c.len_utf8()..).unwrap_or_default();
+            }
+        }
         filled.chars().take(crate::MAX_STAMP_LINE).collect()
     }
 

crates/engine/src/tests.rs

@@ -9420,6 +9420,9 @@ fn repeated_backdrop_artwork_survives_background_undo_redo_and_both_save_modes()
 fn stamp_lines_fill_in_the_name_date_and_time() {
     let s = Session::new().with_clock(|| 1_700_000_000);
     assert_eq!(s.stamp_line("Received {date} {time} by {name}", " Ada "), "Received Nov 14, 2023 10:13 pm by Ada");
+    // Review on #2345 (gabglus): placeholders inside the author's name are kept as written.
+    assert_eq!(s.stamp_line("By {name} — {date} {time}", "Ada {date} {time}"), "By Ada {date} {time} — Nov 14, 2023 10:13 pm");
+    assert_eq!(s.stamp_line("{name}{name}", "{name}"), "{name}{name}");
     assert_eq!(s.stamp_by_line("Ada"), "By Ada at 10:13 pm, Nov 14, 2023");
     assert_eq!(s.stamp_by_line(""), "at 10:13 pm, Nov 14, 2023");
     assert_eq!(s.stamp_line(&"{date}".repeat(100), "Ada").chars().count(), MAX_STAMP_LINE);

crates/ui-egui/tests/it/stamps.rs

@@ -177,6 +177,21 @@ fn a_dynamic_custom_stamp_keeps_its_line_and_fills_it_in_when_placed() {
     h.drop_at(p);
     h.run_steps(4);
     let s = h.state();
+    let saved = s.session.save_bytes(s.views[0].id).unwrap();
+    let pdf = pdfcraft_cos::Document::open(saved).unwrap();
+    let line = pdf
+        .scan_objects()
+        .find_map(|(_, object)| match object.as_ref() {
+            pdfcraft_cos::Object::Dict(dict) => dict.get(b"PCByLine").and_then(pdfcraft_cos::Object::as_string).map(pdfcraft_cos::PdfString::to_text),
+            _ => None,
+        })
+        .expect("placed custom stamp stores PCByLine in the PDF");
+    assert!(line.starts_with("By Ada at "), "expanded stamp line: {line:?}");
+    assert!(
+        !line.contains("{name}") && !line.contains("{date}") && !line.contains("{time}"),
+        "the saved stamp line must not contain unexpanded placeholders: {line:?}"
+    );
+
     let doc = s.session.get(s.views[0].id).unwrap();
     let r = doc.info.annotations.iter().find(|a| a.subtype == "Stamp").expect("placed").rect;
     let aspect = (r[2] - r[0]) / (r[3] - r[1]);