Type: Optical Margin Alignment is a setting of the whole thread

Optical Margin Alignment was stored and set per text object, so the
frames of one thread could differ. Turning it on in the first frame of
a thread left the lines in the other frames flush with their margins.

Type › Optical Margin Alignment and type.opticalMarginAlignment now set
every frame of a selected frame's thread, in one undo step, and the
reply's ids list them all. After any edit to a thread, its frames take
the setting of the frame that the edit turned on or off, else the
first frame's. Threading frames gives the thread its first frame's
setting, and frames taken out of a thread keep it. A file whose frames
of one thread differ opens with the first frame's setting in all of
them. This holds for native files and for documents restored from the
editing copy that an EPS, SVG, PDF or .ai file carries.

Threading text from an out port into existing area type
(text.thread.add with to) now flows the story into that frame at once.
Before, the story reached it only at the next edit of one of the
thread's frames.

Docs: docs/mcp.md, docs/target-app-parity.md, docs/type-parity.md.

crates/engine/src/cmd/threads.rs

@@ -137,6 +137,7 @@ pub(crate) fn reflow(before: &Document, doc: &mut Document) {
                 }
             }
         }
+        let optical = if live.len() >= 2 { optical_margin(before, doc, &live) } else { None };
         let frames: Vec<TextObject> = live.iter().filter_map(|id| text_of(doc, *id).cloned()).collect();
         let refs: Vec<&TextObject> = frames.iter().collect();
         let parts = vectorcraft_text::thread::distribute(vectorcraft_text::FontDb::global(), &refs, &story, &paras);
@@ -145,10 +146,12 @@ pub(crate) fn reflow(before: &Document, doc: &mut Document) {
                 let mut next = (**t).clone();
                 next.runs = part.runs;
                 next.set_paragraph_styles(part.paras);
-                if next.runs != t.runs || next.para != t.para || next.paras != t.paras {
+                let optical = optical.unwrap_or(t.optical_margin);
+                if next.runs != t.runs || next.para != t.para || next.paras != t.paras || optical != t.optical_margin {
                     t.runs = next.runs;
                     t.para = next.para;
                     t.paras = next.paras;
+                    t.optical_margin = optical;
                     refresh_bounds(t);
                 }
             }
@@ -160,6 +163,44 @@ pub(crate) fn reflow(before: &Document, doc: &mut Document) {
     doc.text_threads = kept;
 }
 
+/// The Optical Margin Alignment setting that every frame of a thread with the frames `live` takes:
+/// that of the first frame whose setting changed between `before` and `doc`, else the first frame's.
+fn optical_margin(before: &Document, doc: &Document, live: &[NodeId]) -> Option<bool> {
+    let now = |id: &NodeId| text_of(doc, *id).map(|t| t.optical_margin);
+    let changed = live.iter().find(|id| text_of(before, **id).is_some_and(|t| Some(t.optical_margin) != now(id)));
+    changed.or(live.first()).and_then(now)
+}
+
+/// Give every frame of each thread the first frame's Optical Margin Alignment setting, without
+/// re-flowing the story: for a document restored from a file as it was saved.
+pub(crate) fn share_optical_margin(doc: &mut Document) {
+    for thread in doc.text_threads.clone() {
+        let live: Vec<NodeId> = thread.into_iter().filter(|id| text_of(doc, *id).is_some()).collect();
+        let Some(on) = optical_margin(doc, doc, &live) else { continue };
+        for id in &live {
+            if let Some(NodeKind::Text(t)) = doc.node_mut(*id).map(|n| &mut n.kind)
+                && t.optical_margin != on
+            {
+                t.optical_margin = on;
+                refresh_bounds(t);
+            }
+        }
+    }
+}
+
+/// `ids` followed by the other frames of the threads they are in, each once, in thread order.
+pub(crate) fn with_threads(d: &Document, ids: &[NodeId]) -> Vec<NodeId> {
+    let mut out = ids.to_vec();
+    for thread in d.text_threads.iter().filter(|t| t.iter().any(|id| ids.contains(id))) {
+        for id in thread {
+            if !out.contains(id) && text_of(d, *id).is_some() {
+                out.push(*id);
+            }
+        }
+    }
+    out
+}
+
 /// A closed path converted to an empty area-type frame with `style`.
 fn frame_from_path(n: &Node, style: vectorcraft_doc::CharStyle) -> Option<Node> {
     let NodeKind::Path { path, .. } = &n.kind else { return None };
@@ -280,7 +321,9 @@ fn add(s: &mut Session, p: &Value) -> Result<Value> {
             }
             None => d.text_threads.push(vec![from, to]),
         }
-        // `to` is new or changed, so [`reflow`] flows the story into it after this edit.
+        // Force a re-flow of the thread on this edit: the edit leaves existing area type `to`
+        // unchanged.
+        touch(d, to);
         sel.set([from, to]);
         Ok(to)
     })?;
@@ -550,6 +593,17 @@ mod tests {
         assert_eq!(threads(&s), [[a, c, d]]);
     }
 
+    /// Area type threaded into from an out port takes the overflow at once, before its own text.
+    #[test]
+    fn add_into_area_type_flows_the_story_into_it() {
+        let (mut s, a, _) = setup();
+        let c = new_id(s.execute("text.create", &json!({"x": 10, "y": 100, "text": "Own text.", "area": {"width": 150, "height": 190}})).unwrap());
+        s.execute("text.thread.add", &json!({"from": a, "to": c})).unwrap();
+        assert_eq!(threads(&s), [[a, c]]);
+        assert_eq!(format!("{}{}", text(&s, a), text(&s, c)), format!("{}Own text.", TEXT.repeat(4)));
+        assert!(text(&s, c).len() > "Own text.".len(), "the overflow flowed into the frame: {:?}", text(&s, c));
+    }
+
     #[test]
     fn add_refuses_bad_params_and_leaves_the_document_alone() {
         let (mut s, a, b) = setup();
@@ -595,4 +649,113 @@ mod tests {
         assert_eq!(text(&s, b), "");
         assert_eq!(text(&s, a), TEXT.repeat(4), "the story returns to the remaining frame");
     }
+
+    /// A story of one-line paragraphs that each start with a quotation mark, threaded from area
+    /// type `a` into the rectangle `b`, which shows the paragraphs that `a` has no room for.
+    fn quoted_thread() -> (Session, u64, u64) {
+        let mut s = Session::new();
+        s.execute("file.new", &json!({"width": 600, "height": 300})).unwrap();
+        let story = "“Quoted.”\n".repeat(20);
+        let a = new_id(s.execute("text.create", &json!({"x": 10, "y": 10, "text": story, "area": {"width": 150, "height": 60}})).unwrap());
+        let b = new_id(s.execute("shape.rectangle", &json!({"x": 200, "y": 10, "width": 150, "height": 200})).unwrap());
+        s.execute("select.set", &json!({"ids": [a, b]})).unwrap();
+        s.execute("text.thread.create", &json!({})).unwrap();
+        assert!(text(&s, b).starts_with('“'));
+        (s, a, b)
+    }
+
+    /// Frame `id`'s Optical Margin Alignment setting, and whether its glyphs start left of its frame
+    /// (its lines' opening quotation marks hang).
+    fn optical(s: &Session, id: u64) -> (bool, bool) {
+        let Some(t) = text_of(&s.doc().unwrap().doc, NodeId(id)) else { panic!("not area type") };
+        let TextKind::Area { frame } = &t.kind else { panic!("not area type") };
+        (t.optical_margin, t.cached_bounds.unwrap().x0 < frame.bounds().unwrap().x0 - 1.0)
+    }
+
+    /// Optical Margin Alignment is a setting of the whole thread: Type › Optical Margin Alignment
+    /// in any frame sets it in every frame of the thread, in one undo step, and the lines in every
+    /// frame hang. Typing keeps it, and frames taken out of the thread keep it.
+    #[test]
+    fn optical_margin_alignment_is_set_for_every_frame_of_a_thread() {
+        let (mut s, a, b) = quoted_thread();
+        assert_eq!((optical(&s, a), optical(&s, b)), ((false, false), (false, false)));
+        s.execute("select.set", &json!({"ids": [a]})).unwrap();
+        let r = s.execute("type.opticalMarginAlignment", &json!({})).unwrap();
+        assert_eq!(r, json!({"on": true, "ids": [a, b]}));
+        assert_eq!((optical(&s, a), optical(&s, b)), ((true, true), (true, true)), "the second frame's lines hang too");
+        // Turned off from the second frame, it is off in both, and one undo turns it back on in both.
+        s.execute("select.set", &json!({"ids": [b]})).unwrap();
+        assert_eq!(s.execute("type.opticalMarginAlignment", &json!({})).unwrap()["on"], false);
+        assert_eq!((optical(&s, a), optical(&s, b)), ((false, false), (false, false)));
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!((optical(&s, a), optical(&s, b)), ((true, true), (true, true)));
+        // Typing in the first frame re-flows the story and keeps the setting.
+        s.execute("text.editRange", &json!({"id": a, "start": 0, "end": 0, "insert": "“New.”\n"})).unwrap();
+        assert_eq!((optical(&s, a), optical(&s, b)), ((true, true), (true, true)));
+        // Any edit that sets one frame sets the thread.
+        s.edit("Set", |d, _| {
+            let Some(NodeKind::Text(t)) = d.node_mut(NodeId(b)).map(|n| &mut n.kind) else { panic!("not text") };
+            t.optical_margin = false;
+            refresh_bounds(t);
+            Ok(())
+        })
+        .unwrap();
+        assert_eq!((optical(&s, a), optical(&s, b)), ((false, false), (false, false)));
+        s.execute("edit.undo", &json!({})).unwrap();
+        // Released or unthreaded, each frame keeps it.
+        s.execute("select.set", &json!({"ids": [b]})).unwrap();
+        s.execute("text.thread.releaseSelection", &json!({})).unwrap();
+        assert_eq!((optical(&s, a).0, optical(&s, b).0), (true, true));
+        s.execute("edit.undo", &json!({})).unwrap();
+        s.execute("text.thread.remove", &json!({})).unwrap();
+        assert!(threads(&s).is_empty());
+        assert_eq!((optical(&s, a), optical(&s, b)), ((true, true), (true, true)));
+    }
+
+    /// Threading type into a thread gives the joined thread the setting of its first frame.
+    #[test]
+    fn a_thread_takes_its_first_frames_optical_margin_alignment() {
+        let (mut s, a, b) = quoted_thread();
+        s.execute("text.thread.remove", &json!({})).unwrap();
+        s.execute("type.opticalMarginAlignment", &json!({"ids": [a], "on": true})).unwrap();
+        assert_eq!((optical(&s, a).0, optical(&s, b).0), (true, false));
+        // Threaded again in stacking order: the second frame takes the first one's setting.
+        s.execute("select.set", &json!({"ids": [a, b]})).unwrap();
+        s.execute("text.thread.create", &json!({})).unwrap();
+        assert_eq!((optical(&s, a), optical(&s, b)), ((true, true), (true, true)));
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!((optical(&s, a).0, optical(&s, b).0), (true, false));
+        // From `b`'s out port into `a`: `a` joins `b`'s thread after it and takes its setting.
+        s.execute("text.thread.add", &json!({"from": b, "to": a})).unwrap();
+        assert_eq!(threads(&s), [[b, a]]);
+        assert_eq!((optical(&s, a).0, optical(&s, b).0), (false, false));
+        // A new frame threaded from a frame takes the thread's setting.
+        s.execute("type.opticalMarginAlignment", &json!({"ids": [a], "on": true})).unwrap();
+        let c = new_id(s.execute("text.thread.add", &json!({"from": a, "at": [400, 10]})).unwrap());
+        assert_eq!([a, b, c].map(|id| optical(&s, id).0), [true; 3]);
+    }
+
+    /// A file saved with the frames of one thread set differently opens with the first frame's
+    /// setting in every frame: a native file, and an EPS file restored from the document it carries.
+    #[test]
+    fn a_thread_saved_with_differing_frames_opens_with_the_first_frames_setting() {
+        let (mut s, a, b) = quoted_thread();
+        for (first, name) in [(true, "old.vectorcraft"), (false, "old.vectorcraft"), (true, "old.eps"), (false, "old.eps")] {
+            for (id, on) in [(a, first), (b, !first)] {
+                let doc = std::sync::Arc::make_mut(&mut s.doc_mut().unwrap().doc);
+                let Some(NodeKind::Text(t)) = doc.node_mut(NodeId(id)).map(|n| &mut n.kind) else { panic!("not text") };
+                t.optical_margin = on;
+            }
+            let bytes = if name.ends_with(".eps") {
+                let r = s.execute("document.exportEps", &json!({})).unwrap();
+                vectorcraft_format::base64_decode(r["dataBase64"].as_str().unwrap()).unwrap()
+            } else {
+                vectorcraft_format::save(&s.doc().unwrap().doc, false)
+            };
+            let r = s.execute("document.open", &json!({"name": name, "dataBase64": vectorcraft_format::base64_encode(&bytes)})).unwrap();
+            assert_eq!(r["restored"], name.ends_with(".eps"), "{r}");
+            assert_eq!(threads(&s), [[a, b]], "{name}");
+            assert_eq!((optical(&s, a), optical(&s, b)), ((first, first), (first, first)), "{name}, first frame {first}");
+        }
+    }
 }