Fix reflection property injection reuse

SourceGenerationDebug.props

@@ -1,11 +1,14 @@
 <Project>
     <PropertyGroup>
-        <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
-        <CompilerGeneratedFilesOutputPath>SourceGeneratedViewer</CompilerGeneratedFilesOutputPath>
+        <EmitCompilerGeneratedFiles Condition="'$(EnableSourceGenerationDebug)' == 'true'">true</EmitCompilerGeneratedFiles>
+        <CompilerGeneratedFilesOutputPath Condition="'$(EmitCompilerGeneratedFiles)' == 'true' AND '$(CompilerGeneratedFilesOutputPath)' == ''">SourceGeneratedViewer</CompilerGeneratedFilesOutputPath>
     </PropertyGroup>
 
     <ItemGroup>
         <Compile Remove="SourceGeneratedViewer\**" />
-        <None Include="SourceGeneratedViewer\**" />
+    </ItemGroup>
+
+    <ItemGroup Condition="'$(EmitCompilerGeneratedFiles)' == 'true'">
+        <None Include="SourceGeneratedViewer\**" Exclude="@(None)" />
     </ItemGroup>
 </Project>

TUnit.Engine.Tests/Issue5753Tests.cs

@@ -0,0 +1,21 @@
+using Shouldly;
+using TUnit.Engine.Tests.Enums;
+
+namespace TUnit.Engine.Tests;
+
+public class Issue5753Tests(TestMode testMode) : InvokableTestBase(testMode)
+{
+    [Test]
+    public async Task ReflectionPropertyInjection_DoesNotOverwriteExistingValue()
+    {
+        await RunTestsWithFilter(
+            "/*/*/Issue5753ReflectionPropertyInjectionTests/*",
+            [
+                result => result.ResultSummary.Outcome.ShouldBe("Completed"),
+                result => result.ResultSummary.Counters.Total.ShouldBe(1),
+                result => result.ResultSummary.Counters.Passed.ShouldBe(1),
+                result => result.ResultSummary.Counters.Failed.ShouldBe(0),
+                result => result.ResultSummary.Counters.NotExecuted.ShouldBe(0)
+            ]);
+    }
+}

TUnit.Engine/Services/PropertyInjector.cs

@@ -329,6 +329,11 @@ private async Task InjectReflectionPropertyAsync(
         ConcurrentDictionary<object, byte> visitedObjects,
         CancellationToken cancellationToken)
     {
+        if (property.CanRead && property.GetValue(instance) != null)
+        {
+            return;
+        }
+
         var testContext = TestContext.Current;
         var propertySetter = PropertySetterFactory.CreateSetter(property);
 

TUnit.TestProject/Bugs/5753/Tests.cs

@@ -0,0 +1,41 @@
+using TUnit.Core.Interfaces;
+using TUnit.TestProject.Attributes;
+
+namespace TUnit.TestProject.Bugs._5753;
+
+[EngineTest(ExpectedResult.Pass)]
+public class Issue5753ReflectionPropertyInjectionTests
+{
+    [Test]
+    [ClassDataSource<Issue5753Container>]
+    public async Task InjectedProperty_IsNotResolvedAgain_WhenAlreadySet(Issue5753Container container)
+    {
+        await Assert.That(container.Service).IsNotNull();
+        await Assert.That(container.Service.InstanceNumber).IsEqualTo(1);
+        await Assert.That(Issue5753InjectedService.InstancesCreated).IsEqualTo(1);
+        await Assert.That(container.Service.IsInitialized).IsTrue();
+    }
+}
+
+public class Issue5753Container
+{
+    [ClassDataSource<Issue5753InjectedService>]
+    public Issue5753InjectedService Service { get; set; } = null!;
+}
+
+public class Issue5753InjectedService : IAsyncInitializer
+{
+    private static int _instancesCreated;
+
+    public static int InstancesCreated => Volatile.Read(ref _instancesCreated);
+
+    public int InstanceNumber { get; } = Interlocked.Increment(ref _instancesCreated);
+
+    public bool IsInitialized { get; private set; }
+
+    public Task InitializeAsync()
+    {
+        IsInitialized = true;
+        return Task.CompletedTask;
+    }
+}

TestProject.props

@@ -46,12 +46,11 @@
         <None Include="SourceGeneratedViewer\**" />
     </ItemGroup>
 
-    <!-- Always clean SourceGeneratedViewer\ on local builds when the folder exists.
-         When EmitCompilerGeneratedFiles=true, this gives a fresh dump per build.
-         When EmitCompilerGeneratedFiles=false (the default), this clears stale files
-         left over from a prior opt-in build. CI runners are ephemeral, so skip. -->
+    <!-- Clean SourceGeneratedViewer\ only when generator output is being emitted.
+         Stale files are excluded from compilation unconditionally above, so normal
+         local builds should not fail because an ignored viewer tree is locked. -->
     <Target Name="CleanSourceGeneratedViewer" BeforeTargets="BeforeBuild"
-            Condition="'$(ContinuousIntegrationBuild)' != 'true' AND Exists('$(ProjectDir)SourceGeneratedViewer')">
+            Condition="'$(ContinuousIntegrationBuild)' != 'true' AND '$(EmitCompilerGeneratedFiles)' == 'true' AND Exists('$(ProjectDir)SourceGeneratedViewer')">
         <ItemGroup>
             <FilesToDelete Include="$(ProjectDir)SourceGeneratedViewer\**\*" />
         </ItemGroup>

global.json

@@ -1,7 +1,7 @@
 {
   "sdk": {
     "version": "10.0.203",
-    "rollForward": "latestMajor",
+    "rollForward": "latestFeature",
     "allowPrerelease": true
   },
   "test": {