fix multi-instance entity label display

- fix empty elements created in extendToAllInstances

CHANGELOG.md

@@ -7,6 +7,8 @@ Note that since we don't clearly distinguish between a public and private interf
 ## [Unreleased]
 
 - Fix color smoothing of elongated structures (by fixing ``Sphere.expand`` for spheres with highly directional extrema)
+- Fix entity label not displayed when multiple instances of the same entity are highlighted
+- Fix empty elements created in ``StructureElement.Loci.extendToAllInstances``
 
 ## [v3.0.1] - 2022-01-27
 

src/mol-model/structure/structure/element/loci.ts

 /**
- * Copyright (c) 2017-2021 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ * Copyright (c) 2017-2022 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  * @author David Sehnal <david.sehnal@gmail.com>
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
@@ -497,8 +497,10 @@ export namespace Loci {
             if (!elementIndices) continue;
 
             const indices = getUnitIndices(unit.elements, elementIndices);
+            if (OrderedSet.size(indices)) {
                 elements[elements.length] = { unit, indices };
             }
+        }
 
         return Loci(loci.structure, elements);
     }

src/mol-plugin/behavior/dynamic/representation.ts

 /**
- * Copyright (c) 2018-2021 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ * Copyright (c) 2018-2022 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  * @author David Sehnal <david.sehnal@gmail.com>
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
@@ -212,11 +212,14 @@ export const DefaultLociLabelProvider = PluginBehavior.create({
         private f = {
             label: (loci: Loci) => {
                 const label: string[] = [];
-                if (StructureElement.Loci.is(loci) && loci.elements.length === 1) {
-                    const { unit: u } = loci.elements[0];
+                if (StructureElement.Loci.is(loci)) {
+                    const entityNames = new Set<string>();
+                    for (const { unit: u } of loci.elements) {
                         const l = StructureElement.Location.create(loci.structure, u, u.elements[0]);
                         const name = StructureProperties.entity.pdbx_description(l).join(', ');
-                    label.push(name);
+                        entityNames.add(name);
+                    }
+                    if (entityNames.size === 1) entityNames.forEach(name => label.push(name));
                 }
                 label.push(lociLabel(loci));
                 return label.filter(l => !!l).join('</br>');