Type: an opened file flows its threads in its own composite fonts

Threaded type read from a file was flowed through its frames before
the document's composite fonts were registered, so a story set in one
was measured in the fallback font. Frames then held the wrong share of
the story after opening, until a frame was edited. load_with now lends
the document's composite fonts while it lays out its threads.

crates/engine/src/cmd/compositefonts/tests.rs

@@ -478,6 +478,32 @@ fn an_opened_file_measures_its_type_in_its_own_composite_fonts() {
     assert_eq!(actual.cached_bounds, Some(expected));
 }
 
+/// Threaded type read from a file flows through its frames in the file's own composite fonts, when
+/// no open document defines them.
+#[test]
+fn an_opened_file_flows_its_threads_in_its_own_composite_fonts() {
+    let mut s = session();
+    s.execute("type.compositeFonts.set", &json!({"fonts": [font("CF Threaded")]})).unwrap();
+    let story = "The quick brown fox jumps over the lazy dog and keeps running. ".repeat(4);
+    let a = s
+        .execute("text.create", &json!({"x": 10, "y": 10, "text": story, "size": 20, "font": "CF Threaded", "area": {"width": 150, "height": 60}}))
+        .unwrap()["id"]
+        .as_u64()
+        .unwrap();
+    let b = s.execute("shape.rectangle", &json!({"x": 200, "y": 10, "width": 150, "height": 300})).unwrap()["id"].as_u64().unwrap();
+    s.execute("select.set", &json!({"ids": [a, b]})).unwrap();
+    s.execute("text.thread.create", &json!({})).unwrap();
+    let first = text(&s, a).plain_text();
+    assert!(!first.is_empty() && first.len() < story.len());
+    let bytes = vectorcraft_format::save_file(&s.doc().unwrap().doc);
+    // A new front document without the font: the font database no longer holds it.
+    s.execute("file.new", &json!({"width": 100, "height": 100})).unwrap();
+    assert!(vectorcraft_text::FontDb::global().composite_font("CF Threaded").is_none());
+    let file = crate::cmd::fileio::read_for_open("threaded.vectorcraft", &bytes, None, &json!({}), false, false).unwrap();
+    crate::cmd::fileio::open_read(&mut s, file).unwrap();
+    assert_eq!(text(&s, a).plain_text(), first);
+}
+
 /// A document replaced while in the back (File › Revert) is measured in its own composite fonts
 /// when it comes to the front, not in the front document's.
 #[test]

crates/engine/src/cmd/fileio/load.rs

@@ -506,7 +506,10 @@ pub fn load_with(name: &str, bytes: &[u8], opts: &LoadOptions) -> Result<Loaded>
     // document keeps its text as saved), and every frame of a thread takes its first frame's
     // Optical Margin Alignment setting and writing direction. When that changes the direction of a
     // frame of a restored document, the story flows through that frame's thread again. Threaded
-    // frames keep their size: Auto Size is off for them.
+    // frames keep their size: Auto Size is off for them. The story is laid out in the document's
+    // own composite fonts.
+    let fonts = if doc.text_threads.is_empty() { Default::default() } else { doc.composite_fonts.clone() };
+    let lent = vectorcraft_text::FontDb::global().lend_composite_fonts(&fonts);
     if !doc.text_threads.is_empty() && !restored {
         crate::cmd::threads::reflow(&Document::new(1.0, 1.0), &mut doc);
     } else if !doc.text_threads.is_empty() {
@@ -517,6 +520,7 @@ pub fn load_with(name: &str, bytes: &[u8], opts: &LoadOptions) -> Result<Loaded>
         // paragraph's first-line indent and list marker.
         crate::cmd::threads::mark_continued(&mut doc);
     }
+    drop(lent);
     if let Some(mode) = opts.color_mode.filter(|m| *m != doc.color_mode) {
         super::super::colormgmt::set_color_mode(&mut doc, mode, true, None, opts.grays);
     }