Fix for issue 15598 (#15617)

* Make GetIndexValues virtual

* First try get values as JSON. If empty, try as CSV.

src/Umbraco.Core/PropertyEditors/JsonPropertyIndexValueFactoryBase.cs

@@ -40,7 +40,7 @@ public abstract class JsonPropertyIndexValueFactoryBase<TSerialized> : IProperty
 
     }
 
-    public IEnumerable<KeyValuePair<string, IEnumerable<object?>>> GetIndexValues(
+    public virtual IEnumerable<KeyValuePair<string, IEnumerable<object?>>> GetIndexValues(
         IProperty property,
         string? culture,
         string? segment,

src/Umbraco.Core/PropertyEditors/TagPropertyIndexValueFactory.cs

@@ -1,20 +1,26 @@
+using System.Text.Json;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using Umbraco.Cms.Core.Configuration.Models;
 using Umbraco.Cms.Core.Models;
 using Umbraco.Cms.Core.Serialization;
 using Umbraco.Cms.Web.Common.DependencyInjection;
+using Umbraco.Extensions;
 
 namespace Umbraco.Cms.Core.PropertyEditors;
 
 public class TagPropertyIndexValueFactory : JsonPropertyIndexValueFactoryBase<string[]>, ITagPropertyIndexValueFactory
 {
+    private IndexingSettings _indexingSettings;
+
     public TagPropertyIndexValueFactory(
         IJsonSerializer jsonSerializer,
         IOptionsMonitor<IndexingSettings> indexingSettings)
         : base(jsonSerializer, indexingSettings)
     {
         ForceExplicitlyIndexEachNestedProperty = true;
+        _indexingSettings = indexingSettings.CurrentValue;
+        indexingSettings.OnChange(newValue => _indexingSettings = newValue);
     }
 
     [Obsolete("Use non-obsolete constructor. This will be removed in Umbraco 14.")]
@@ -45,4 +51,40 @@ public class TagPropertyIndexValueFactory : JsonPropertyIndexValueFactoryBase<st
     {
         yield return new KeyValuePair<string, IEnumerable<object?>>(property.Alias, deserializedPropertyValue);
     }
+
+    public override IEnumerable<KeyValuePair<string, IEnumerable<object?>>> GetIndexValues(
+        IProperty property,
+        string? culture,
+        string? segment,
+        bool published,
+        IEnumerable<string> availableCultures,
+        IDictionary<Guid, IContentType> contentTypeDictionary)
+    {
+        IEnumerable<KeyValuePair<string, IEnumerable<object?>>> jsonValues = base.GetIndexValues(property, culture, segment, published, availableCultures, contentTypeDictionary);
+        if (jsonValues?.Any() is true)
+        {
+            return jsonValues;
+        }
+
+        var result = new List<KeyValuePair<string, IEnumerable<object?>>>();
+
+        var propertyValue = property.GetValue(culture, segment, published);
+
+        // If there is a value, it's a string and it's not empty/white space
+        if (propertyValue is string rawValue && !string.IsNullOrWhiteSpace(rawValue))
+        {
+            var values = rawValue.Split(',', StringSplitOptions.RemoveEmptyEntries);
+
+            result.AddRange(Handle(values, property, culture, segment, published, availableCultures, contentTypeDictionary));
+        }
+
+        IEnumerable<KeyValuePair<string, IEnumerable<object?>>> summary = HandleResume(result, property, culture, segment, published);
+        if (_indexingSettings.ExplicitlyIndexEachNestedProperty || ForceExplicitlyIndexEachNestedProperty)
+        {
+            result.AddRange(summary);
+            return result;
+        }
+
+        return summary;
+    }
 }