[mob][photos] Show smaller people clusters for small libraries

mobile/lib/services/machine_learning/face_ml/face_filtering/face_filtering_constants.dart

@@ -18,3 +18,6 @@ const kMinFaceDetectionScore = FaceDetectionService.kMinScoreSigmoidThreshold;
 
 /// The minimum cluster size for displaying a cluster in the UI
 const kMinimumClusterSizeSearchResult = 10;
+
+/// The minimum cluster sizes to try when the normal minimum doesn't return any results
+const kLowerMinimumClusterSizes = [5, 3, 2, 1];

mobile/lib/services/search_service.dart

@@ -765,7 +765,10 @@ class SearchService {
     return clusterIDToFiles;
   }
 
-  Future<List<GenericSearchResult>> getAllFace(int? limit) async {
+  Future<List<GenericSearchResult>> getAllFace(
+    int? limit, {
+    int minClusterSize = kMinimumClusterSizeSearchResult,
+  }) async {
     try {
       debugPrint("getting faces");
       final Map<int, Set<String>> fileIdToClusterID =
@@ -857,10 +860,7 @@ class SearchService {
             "`getAllFace`: Cluster $clusterId should not have person id ${clusterIDToPersonID[clusterId]}",
           );
         }
-        if (files.length < kMinimumClusterSizeSearchResult &&
-            sortedClusterIds.length > 3) {
-          continue;
-        }
+        if (files.length < minClusterSize) continue;
         facesResult.add(
           GenericSearchResult(
             ResultType.faces,
@@ -883,6 +883,20 @@ class SearchService {
           ),
         );
       }
+      if (facesResult.isEmpty) {
+        int newMinimum = minClusterSize;
+        for (final int minimum in kLowerMinimumClusterSizes) {
+          if (minimum < minClusterSize) {
+            newMinimum = minimum;
+            break;
+          }
+        }
+        if (newMinimum < minClusterSize) {
+          return getAllFace(limit, minClusterSize: newMinimum);
+        } else {
+          return [];
+        }
+      }
       if (limit != null) {
         return facesResult.sublist(0, min(limit, facesResult.length));
       } else {

mobile/lib/ui/viewer/search_tab/people_section.dart

@@ -30,10 +30,10 @@ class PeopleSection extends StatefulWidget {
   final int limit;
 
   const PeopleSection({
-    Key? key,
+    super.key,
     required this.examples,
     this.limit = 7,
-  }) : super(key: key);
+  });
 
   @override
   State<PeopleSection> createState() => _PeopleSectionState();