Selection colors: Create style refuses a row whose fill or stroke list holds other paints

A created style holds the row's one paint, and linking it replaces the target's whole fill or
stroke list, so a layer with other fills or strokes lost them. selection.createColorStyle now
refuses such targets before any change, and the Styles menu leaves Create style out for those
rows.

crates/engine/src/selection/selection_colors.rs

@@ -134,7 +134,7 @@ pub fn specs() -> Vec<CommandSpec> {
         spec!(
             "selection.createColorStyle",
             "Create selection color style",
-            "{targets, name, description?} → {id}; makes a color style of the paint the targets share and applies it to them as selection.applyColorStyle does; a name another style has is refused",
+            "{targets, name, description?} → {id}; makes a color style of the paint the targets share and applies it to them as selection.applyColorStyle does; a name another style has, or a target whose list holds other paints, is refused",
             true,
             create_style
         ),
@@ -252,6 +252,9 @@ fn create_style(s: &mut Session, p: &Value) -> Result<Value> {
     if targets.iter().any(|t| t.paint(doc).as_ref() != Some(&paint)) {
         return Err(bad(CMD, "the targets no longer share one paint"));
     }
+    if let Some(why) = create_refusal(doc, &targets) {
+        return Err(bad(CMD, why));
+    }
     let name = crate::cmd::variables::clean_name(&req_string(CMD, p, "name")?).ok_or_else(|| bad(CMD, "name can't be empty"))?;
     if doc.styles.iter().any(|st| st.name == name) {
         return Err(bad(CMD, format!("a style named `{name}` already exists")));
@@ -270,6 +273,16 @@ fn create_style(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(json!({"id": id}))
 }
 
+/// Why a color style can't be made from `targets` (`selection.createColorStyle`), if it can't: a
+/// linked style replaces the whole fill or stroke list, so a target whose list holds other paints
+/// would lose them. The Selection colors menu leaves Create style out for such rows.
+pub fn create_refusal(doc: &Document, targets: &[PaintTarget]) -> Option<&'static str> {
+    targets
+        .iter()
+        .any(|t| t.paints(doc).is_none_or(|paints| paints.len() != 1))
+        .then_some("a style can only be made from a fill or stroke list that holds this one paint")
+}
+
 /// Apply paint style `style` to every target: a fill or stroke list is linked to it; a text range
 /// takes its resolved paints and keeps its typography.
 fn link_style(s: &mut Session, targets: &[PaintTarget], style: &Style) -> Result<()> {

crates/engine/tests/it/selection_colors.rs

@@ -2,7 +2,7 @@ use figcraft_color::Paint;
 use figcraft_doc::NodeId;
 use figcraft_engine::{
     Session,
-    selection_colors::{SelectionColor, collect},
+    selection_colors::{self, SelectionColor, collect},
 };
 use serde_json::{Value, json};
 
@@ -505,6 +505,30 @@ fn creating_a_style_refuses_taken_or_empty_names_and_stale_rows_and_changes_noth
     assert_eq!(fill(&s, a), "FF0000");
 }
 
+#[test]
+fn creating_a_style_refuses_a_row_whose_list_holds_other_paints() {
+    let mut s = Session::new();
+    let a = rectangle(&mut s, "#ff0000");
+    let b = rectangle(&mut s, "#ff0000");
+    run(&mut s, "fill.add", json!({"id":a,"paint":"#0000ff"}));
+    let red = group(&s, &[a, b], "FF0000");
+    let before = s.undo_depth();
+    let styles = s.doc().unwrap().styles.len();
+    let err = s.execute("selection.createColorStyle", &json!({"targets":red.targets,"name":"Red"})).unwrap_err();
+    assert!(err.to_string().contains("holds this one paint"), "{err}");
+    assert!(selection_colors::create_refusal(s.doc().unwrap(), &red.targets).is_some());
+    assert_eq!(s.undo_depth(), before);
+    let doc = s.doc().unwrap();
+    assert_eq!(doc.styles.len(), styles);
+    assert_eq!(doc.node(a).unwrap().fills.len(), 2, "the layer keeps its other fill");
+    assert!(doc.node(b).unwrap().styles.fill.is_none());
+    // The single-paint layer alone still makes a style.
+    let b_only: Vec<_> = red.targets.iter().filter(|t| t.id == b).cloned().collect();
+    assert!(selection_colors::create_refusal(s.doc().unwrap(), &b_only).is_none());
+    run(&mut s, "selection.createColorStyle", json!({"targets":b_only,"name":"Red"}));
+    assert!(s.doc().unwrap().node(b).unwrap().styles.fill.is_some());
+}
+
 #[test]
 fn a_linked_row_switches_to_another_style() {
     let mut s = Session::new();

crates/ui-egui/src/panels/selection_colors.rs

@@ -7,7 +7,7 @@ use egui::{Id, Ui};
 use figcraft_color::{Color, Paint};
 use figcraft_doc::{Document, NodeId, PublishedLibrary, Style, StyleKind, VariableType};
 use figcraft_engine::library;
-use figcraft_engine::selection_colors::{PaintTarget, SelectionColor, bind_refusal, collect, in_scope};
+use figcraft_engine::selection_colors::{PaintTarget, SelectionColor, bind_refusal, collect, create_refusal, in_scope};
 use serde_json::json;
 
 use crate::a11y::Tip;
@@ -122,7 +122,7 @@ pub fn section(app: &mut FigApp, ui: &mut Ui, doc: &Arc<Document>, ids: &[NodeId
                             style_items(app, ui, doc, group, &t);
                             if linked_name.is_none() {
                                 ui.separator();
-                                if crate::right::menu_item(ui, tr("Create style"), "") {
+                                if create_refusal(doc, &group.targets).is_none() && crate::right::menu_item(ui, tr("Create style"), "") {
                                     open_create_form(app, ui, doc, group);
                                     ui.close();
                                 }
@@ -536,6 +536,17 @@ mod tests {
         assert!(p.frame(vec![]).iter().any(|(s, _)| s == "Brand"));
     }
 
+    #[test]
+    fn create_style_is_left_out_for_a_row_whose_list_holds_other_paints() {
+        let (mut p, a, _) = Panel::new();
+        p.app.run("fill.add", json!({"id":a,"paint":"#00ff00"}));
+        let red = text_at(&p.frame(vec![]), "FF0000");
+        p.click(Pos2::new(228.0, red.y));
+        let texts = p.frame(vec![]);
+        assert!(texts.iter().any(|(s, _)| s == "No color styles"), "the Styles menu opens");
+        assert!(!texts.iter().any(|(s, _)| s == "Create style"));
+    }
+
     #[test]
     fn a_linked_rows_styles_menu_switches_its_style() {
         let (mut p, a, _) = Panel::new();