M6: the .fig export names the case of a multi-line instance text on its main's text path (#2323)

An override can't take its layer off the main component's text path, so an instance text of more than one line, whose main is on a path, stays on that path in the file. The export warned the general instance mismatch for it. It now says exactly that case: "an instance's text of more than one line stays on its main component's text path in the file, as an override can't take it off". FigCraft's own import reads such a layer as plain text. The docs' Left out list names the case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Model-Effort: Opus 5.5 drove and wrote

crates/format/src/fig/export/shape.rs

@@ -381,7 +381,11 @@ impl<'d> Exporter<'d> {
         if let Some(main) = main {
             let main_ok = matches!(&main.kind, NodeKind::Text(m) if text_path_net(m, main.width, main.height).is_ok());
             if main_ok != own.is_ok() {
-                self.warn(TEXT_PATH_INSTANCE);
+                // An override can't take its layer off the main's path. So an instance text of
+                // more than one line, on a main that is on a path, stays on that path in the file:
+                // say so rather than the general mismatch (FigCraft's import reads it as plain text).
+                let lines = main_ok && matches!(own, Err(TEXT_PATH_LINES));
+                self.warn(if lines { TEXT_PATH_INSTANCE_LINES } else { TEXT_PATH_INSTANCE });
                 return None;
             }
         }
@@ -414,6 +418,8 @@ const TEXT_PATH_CANT: &str = "text on a path the format can't hold was written a
 const TEXT_PATH_PARTS: &str = "the parts of a text's path after the first were left out";
 const TEXT_PATH_INSTANCE: &str =
     "text on a path in an instance but not in its main component, or the other way round, was written as the main has it";
+const TEXT_PATH_INSTANCE_LINES: &str =
+    "an instance's text of more than one line stays on its main component's text path in the file, as an override can't take it off";
 
 /// A text's path as the format holds it: one chain (or cycle) of a vector network with the
 /// segment the text starts on marked, and the start as that segment's own parameter.

crates/format/src/fig/text_path_tests.rs

@@ -275,6 +275,8 @@ const W1: &str = "text on a path with more than one line was written as plain te
 const W2: &str = "text on a path the format can't hold was written as plain text";
 const W3: &str = "the parts of a text's path after the first were left out";
 const W4: &str = "text on a path in an instance but not in its main component, or the other way round, was written as the main has it";
+const W4_LINES: &str =
+    "an instance's text of more than one line stays on its main component's text path in the file, as an override can't take it off";
 const MARK: u32 = 0x01ff_ffff;
 
 /// What an export wrote: its warnings, the layer records and the blobs.
@@ -557,6 +559,15 @@ fn an_instance_layer_on_a_path_survives_a_fig_export() {
     let (back, _) = super::import(&bytes, "Back").unwrap();
     assert_eq!(path_of(&back, "Half").as_deref(), Some("M0,0 L50,0"));
 
+    // An instance's text of two lines on a main that is on a path: the override can't leave the
+    // path, so the warning names that case, not the general mismatch.
+    let mut two = doc.clone();
+    let id: NodeId = two.nodes().find(|n| n.name == "Half").unwrap().children[0];
+    two.node_mut(id).unwrap().kind.text_mut().unwrap().characters = "al\npha".into();
+    let (_, w) = Written::of(&two);
+    assert!(w.warned(W4_LINES), "{:?}", w.warnings);
+    assert!(!w.warned(W4), "{:?}", w.warnings);
+
     // The other way round: the main's layer is plain text, and so is the instance's.
     let (bytes, w) = Written::of(&off("Main"));
     assert!(w.warned(W4), "{:?}", w.warnings);

docs/file-format-parity.md

@@ -141,7 +141,7 @@ scales and empty-style clears; they have not been checked in other software.
   with the width on both sides when the shape has a fill too), pattern fills, WebP export settings (written as PNG),
   image adjustments, glass settings other than frost, springs other than Gentle (written as ease
   out), set-variable, set-variable-mode and conditional actions, scroll-to offsets, text decoration
-  looks, variable font axes, text on a path with more than one line or on a path the format can't hold (written as plain text), the parts of a text's path after the first, text on a path in an instance but not in its main or the other way round (written as the main has it), nested list levels, OpenType features, per-layer operations inside boolean groups, different stroke ends
+  looks, variable font axes, text on a path with more than one line or on a path the format can't hold (written as plain text), the parts of a text's path after the first, text on a path in an instance but not in its main or the other way round (written as the main has it), an instance's text of more than one line on a main on a path (it stays on that path, as an override can't take it off), nested list levels, OpenType features, per-layer operations inside boolean groups, different stroke ends
   on lines, the Dash cap (no public name for it). Not written at all: stroke outlines of dashed and per-side strokes and of inside or
   outside strokes on polygons, stars and vectors, glyph outlines of text (a reader lays text out
   with its own fonts), version history and branches.