throw exception if duplicate content app aliases are found

src/Umbraco.Web/ContentApps/ContentAppDefinitionCollection.cs

@@ -1,20 +1,43 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using Umbraco.Core;
 using Umbraco.Core.Composing;
 using Umbraco.Core.Models.ContentEditing;
+using Umbraco.Core.Logging;
 
 namespace Umbraco.Web.ContentApps
 {
     public class ContentAppDefinitionCollection : BuilderCollectionBase<IContentAppDefinition>
     {
+        //private readonly ILogger _logger;
+
         public ContentAppDefinitionCollection(IEnumerable<IContentAppDefinition> items)
             : base(items)
-        { }
+        {
+            //_logger = logger;
+        }
 
         public IEnumerable<ContentApp> GetContentAppsFor(object o)
         {
-            return this.Select(x => x.GetContentAppFor(o)).WhereNotNull().OrderBy(x => x.Weight);
+            var apps = this.Select(x => x.GetContentAppFor(o)).WhereNotNull().OrderBy(x => x.Weight);
+            //apps must have unique aliases, we will remove any duplicates and log problems
+            var resultApps = new Dictionary<string, ContentApp>();
+            List<string> dups = null;
+            foreach(var a in apps)
+            {
+                if (resultApps.TryGetValue(a.Alias, out var count))
+                    (dups ?? (dups = new List<string>())).Add(a.Alias);
+                else
+                    resultApps[a.Alias] = a;
+            }
+            if (dups != null)
+            {
+                throw new InvalidOperationException($"Duplicate content app aliases found: {string.Join(",", dups)}");
+                //_logger.Warn<ContentAppDefinitionCollection>($"Duplicate content app aliases found: {string.Join(",", dups)}");
+            }
+
+            return resultApps.Values;
         }
     }
 }