M3: an effects key naming no effect's field binds nothing (#2055)

Review follow-up: `effects/x/radius`, `effects/0` and `effects` name no
effect's field, but `list_binding` doesn't parse them, so the layer's
check took them for some other field and kept an inert binding. A key
under `effects` that names no effect's field is now refused as well.

crates/engine/src/binding_lists_tests.rs

@@ -134,12 +134,15 @@ fn a_layer_binds_only_fields_its_effects_have() {
     let (mut s, r) = setup();
     ex(&mut s, "effect.add", json!({"ids": [r], "type": "dropShadow"}));
     ex(&mut s, "effect.add", json!({"ids": [r], "type": "glass"}));
-    // As an effect style does: a drop shadow has no refraction, glass no spread, and there is no
-    // effect 5. Nothing is bound.
+    // As an effect style does: a drop shadow has no refraction, glass no spread, there is no
+    // effect 5, and a key that names no effect's field names nothing. Nothing is bound.
     for (field, var, says) in [
         ("effects/0/refraction", "large", "no field"),
         ("effects/1/spread", "large", "no field"),
         ("effects/5/radius", "large", "no field"),
+        ("effects/x/radius", "large", "no field"),
+        ("effects/0", "large", "no field"),
+        ("effects", "large", "no field"),
         ("effects/1/lightAngle", "brand", "doesn't take a color variable"),
         ("effects/0/color", "large", "doesn't take a number variable"),
     ] {

crates/engine/src/cmd/variables.rs

@@ -661,11 +661,12 @@ fn effect_field(doc: &Document, node: NodeId, i: usize, field: &str) -> Option<V
 }
 
 /// Whether `node` has the field a binding key names. Only effect fields are checked: a layer has
-/// `effects/<i>/<field>` when its effect `i` has that field (a drop shadow has no `refraction`).
+/// `effects/<i>/<field>` when its effect `i` has that field (a drop shadow has no `refraction`),
+/// and an `effects…` key naming no effect's field (`effects/x/radius`, `effects/0`) has none.
 pub fn has_field(doc: &Document, node: NodeId, field: &str) -> bool {
     match super::lists::list_binding(field) {
         Some((BoundList::Effects, i, f)) => effect_field(doc, node, i, f).is_some(),
-        _ => true,
+        _ => field.split('/').next() != Some(BoundList::Effects.prefix()),
     }
 }