Global swatch edits reach opacity-mask art (#1735)

A mask's art lives outside the layer tree (in the masked object's extras),
and the walks over linked colours skipped it: editing a global swatch
recoloured everything but the mask, which kept showing (or hiding) as
before, and a swatch used only in a mask counted as unused. The colour
walks now go into opacity masks: map_solid_paints (swatch edits, renames,
deletes, Merge and the like) and visit_paints (unused swatches).

crates/doc/src/swatches.rs

@@ -109,10 +109,11 @@ impl Document {
     }
 
     /// Visit every colour that can link to a swatch — solid paints and gradient stops of fills,
-    /// strokes and text runs — in the art, symbol definitions, pattern tiles, graphic styles and the
-    /// swatches themselves (tint swatches, gradient swatches' stops). `f(colour, link, tint)` may
-    /// change them and returns true when it did ([`Paint::map_links`]). Only nodes holding a changed
-    /// paint (and the paths to them) are copied. Returns the number of changed paints.
+    /// strokes and text runs — in the art (opacity masks included), symbol definitions, pattern
+    /// tiles, graphic styles and the swatches themselves (tint swatches, gradient swatches' stops).
+    /// `f(colour, link, tint)` may change them and returns true when it did
+    /// ([`Paint::map_links`]). Only nodes holding a changed paint (and the paths to them) are
+    /// copied. Returns the number of changed paints.
     pub fn map_solid_paints(&mut self, f: &mut LinkFn) -> usize {
         let mut n = map_trees(&mut self.layers, f);
         for s in &mut self.symbols {
@@ -152,11 +153,12 @@ impl Document {
 }
 
 impl Document {
-    /// Visit every paint held by the art, symbol definitions, pattern tiles and graphic styles
-    /// (fills, strokes and text runs), and the colour of every gradient-mesh point as a solid paint.
+    /// Visit every paint held by the art (opacity masks included), symbol definitions, pattern
+    /// tiles and graphic styles (fills, strokes and text runs), and the colour of every
+    /// gradient-mesh point as a solid paint.
     pub fn visit_paints(&self, f: &mut dyn FnMut(&Paint)) {
         let mut tree = |n: &Node| {
-            n.walk(&mut |m| {
+            walk_with_masks(n, &mut |m| {
                 node_paints(m).for_each(&mut *f);
                 if let NodeKind::Mesh(mesh) = &m.kind {
                     mesh.points.iter().for_each(|p| f(&Paint::solid(p.color)));
@@ -280,9 +282,31 @@ fn map_node(n: &Node, f: &mut LinkFn) -> Option<(Node, usize)> {
             }
         }
     }
+    // Opacity mask art lives outside the tree, but its colours are the object's too (#1735).
+    if let Some(mask) = n.extras().mask.as_deref()
+        && let Some((new, k)) = map_node(&mask.art, f)
+    {
+        let m = out.get_or_insert_with(|| n.clone());
+        if let Some(slot) = m.extras_if_any().and_then(|e| e.mask.as_deref_mut()) {
+            slot.art = Arc::new(new);
+            count += k;
+        }
+    }
     out.map(|m| (m, count))
 }
 
+/// Visit `n` and its subtree, the art of opacity masks included (mask art after the masked
+/// object, before its children).
+fn walk_with_masks<'a>(n: &'a Node, f: &mut dyn FnMut(&'a Node)) {
+    f(n);
+    if let Some(mask) = n.extras().mask.as_deref() {
+        walk_with_masks(&mask.art, f);
+    }
+    for c in n.children().into_iter().flatten() {
+        walk_with_masks(c, f);
+    }
+}
+
 fn map_tree(n: &mut Arc<Node>, f: &mut LinkFn) -> usize {
     match map_node(n, f) {
         Some((new, count)) => {

crates/engine/src/tests_swatches.rs

@@ -353,3 +353,33 @@ fn a_group_from_a_mesh_holds_its_point_colours() {
     let names = r["swatches"].as_array().unwrap();
     assert!(names.contains(&json!("R=255 G=0 B=0")) && names.contains(&json!("R=255 G=255 B=255")), "{r}");
 }
+
+/// #1735: a global swatch edit reaches opacity-mask art: the mask's colour (and with it what the
+/// mask shows) follows the swatch, and a swatch used only in a mask isn't "unused".
+#[test]
+fn global_swatch_edits_reach_opacity_mask_art() {
+    let mut s = session();
+    run(&mut s, "swatch.new", json!({"name": "MaskTone", "color": "#ffffff", "global": true}));
+    let obj = rect(&mut s);
+    run(&mut s, "paint.setFill", json!({"color": "#ff0000", "ids": [obj.0]}));
+    let m = rect(&mut s);
+    run(&mut s, "paint.setFill", json!({"swatch": "MaskTone", "ids": [m.0]}));
+    run(&mut s, "select.set", json!({"ids": [obj.0, m.0]}));
+    run(&mut s, "transparency.makeOpacityMask", json!({"clip": true, "invert": false}));
+    let mask_fill = |s: &Session| {
+        let n = doc(s).node(obj).unwrap();
+        n.extras().mask.as_deref().unwrap().art.appearance.fill_paint()
+    };
+    assert_eq!(mask_fill(&s).color(), Some(Color::rgb(1.0, 1.0, 1.0)));
+    assert!(!run(&mut s, "swatch.unused", json!({}))["names"].as_array().unwrap().iter().any(|n| n == "MaskTone"), "used by the mask");
+
+    let r = run(&mut s, "swatch.edit", json!({"name": "MaskTone", "color": "#000000"}));
+    assert_eq!(r["relinked"], 1, "{r}");
+    let fill = mask_fill(&s);
+    assert_eq!(fill.color(), Some(Color::rgb(0.0, 0.0, 0.0)));
+    assert!(matches!(&fill, Paint::Solid { swatch: Some(n), .. } if n == "MaskTone"), "{fill:?}");
+
+    // Undo brings the mask's colour back with the swatch.
+    run(&mut s, "edit.undo", json!({}));
+    assert_eq!(mask_fill(&s).color(), Some(Color::rgb(1.0, 1.0, 1.0)));
+}