Keep Scoop source placeholders valid across source reloads

src/UniGetUI.PackageEngine.PackageManagerClasses/Manager/Classes/SourceFactory.cs

@@ -7,6 +7,7 @@ public class SourceFactory : ISourceFactory
     {
         private readonly IPackageManager __manager;
         private readonly ConcurrentDictionary<string, IManagerSource> __reference;
+        private readonly ConcurrentDictionary<string, IManagerSource> __placeholders = [];
         private readonly Uri __default_uri = new("https://devolutions.net/unigetui");
 
         public SourceFactory(IPackageManager manager)
@@ -32,9 +33,11 @@ public IManagerSource GetSourceOrDefault(string name)
                 return source;
             }
 
-            ManagerSource new_source = new(__manager, name, __default_uri);
-            __reference.TryAdd(name, new_source);
-            return new_source;
+            IManagerSource new_source = __placeholders.GetOrAdd(
+                name,
+                n => new ManagerSource(__manager, n, __default_uri)
+            );
+            return __reference.GetOrAdd(name, new_source);
         }
 
         /// <summary>
@@ -60,6 +63,15 @@ public void AddSource(IManagerSource source)
                     existing_source.ReplaceUrl(source.Url);
                 }
             }
+
+            // Placeholders handed out before a Reset() are still referenced by packages
+            if (__placeholders.TryRemove(source.Name, out IManagerSource? placeholder))
+            {
+                if (placeholder.Url == __default_uri)
+                {
+                    placeholder.ReplaceUrl(source.Url);
+                }
+            }
         }
 
         public IManagerSource[] GetAvailableSources()

src/UniGetUI.PackageEngine.Tests/SourceFactoryTests.cs

@@ -0,0 +1,37 @@
+using UniGetUI.PackageEngine.Interfaces;
+using UniGetUI.PackageEngine.Tests.Infrastructure.Builders;
+
+namespace UniGetUI.PackageEngine.Tests;
+
+public sealed class SourceFactoryTests
+{
+    [Fact]
+    public void PlaceholderHandedOutBeforeResetReceivesRealUrlFromAddSource()
+    {
+        var manager = new PackageManagerBuilder().Build();
+        var factory = manager.SourcesHelper.Factory;
+        IManagerSource placeholder = factory.GetSourceOrDefault("main");
+
+        factory.Reset();
+        var real = new SourceBuilder()
+            .WithManager(manager)
+            .WithName("main")
+            .WithUrl("https://github.com/ScoopInstaller/Main")
+            .Build();
+        factory.AddSource(real);
+
+        Assert.Equal(real.Url, placeholder.Url);
+    }
+
+    [Fact]
+    public void PlaceholderRequestedAfterResetIsTheSameInstanceAsBefore()
+    {
+        var manager = new PackageManagerBuilder().Build();
+        var factory = manager.SourcesHelper.Factory;
+        IManagerSource before = factory.GetSourceOrDefault("main");
+
+        factory.Reset();
+
+        Assert.Same(before, factory.GetSourceOrDefault("main"));
+    }
+}