Don't overwrite LangVersion if set and check raise diagnostic error if level not high enough

TUnit.Core.SourceGenerator/CodeGenerators/LanguageVersionCheckGenerator.cs

@@ -0,0 +1,42 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+
+namespace TUnit.Core.SourceGenerator;
+
+[Generator]
+public class LanguageVersionCheckGenerator : IIncrementalGenerator
+{
+    public void Initialize(IncrementalGeneratorInitializationContext context)
+    {
+        var settings = context.CompilationProvider
+            .Select((c, _)  => 
+            {
+                LanguageVersion? csharpVersion = c is CSharpCompilation comp
+                    ? comp.LanguageVersion
+                    : null;
+
+                return csharpVersion;
+            });
+
+        context.RegisterSourceOutput(settings, static (sourceProductionContext, languageVersion) =>
+        {
+            if (languageVersion is null)
+            {
+                return;
+            }
+
+            if((int)languageVersion.Value < 1200)
+            {
+                sourceProductionContext.ReportDiagnostic(Diagnostic.Create(
+                    new DiagnosticDescriptor(
+                        "TUNIT_LANG_001",
+                        "Language Version Check",
+                        "TUnit requires C# 12 or higher when using Source Generation.",
+                        "Usage",
+                        DiagnosticSeverity.Error,
+                        true),
+                    Location.None));
+            }
+        });
+    }
+}

TUnit.Engine/TUnit.Engine.props

@@ -7,7 +7,6 @@
         <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
         <TestingPlatformShowTestsFailure>true</TestingPlatformShowTestsFailure>
         <TestingPlatformCaptureOutput>false</TestingPlatformCaptureOutput>
-        <LangVersion>latest</LangVersion>
         <OutputType>Exe</OutputType>
         <GenerateProgramFile>false</GenerateProgramFile>
     </PropertyGroup>

TUnit.Engine/TUnit.Engine.targets

@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
-
+
+    <PropertyGroup>
+        <LangVersion Condition="'$(LangVersion)' == ''">latest</LangVersion>
+    </PropertyGroup>
+
     <ItemGroup Condition="'$(TUnitImplicitUsings)' == 'true'">
         <Using Include="TUnit.Core" />
     </ItemGroup>
@@ -13,4 +17,4 @@
         <AssemblyMetadata Include="TUnitReflectionScanner" Value="true" />
     </ItemGroup>
 
-</Project>
+</Project>

TUnit.TestProject.VB.NET/TUnit.TestProject.VB.NET.vbproj

@@ -1,5 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+    <PropertyGroup>
+        <LangVersion>latest</LangVersion>
+    </PropertyGroup>
+
     <Import Project="..\TestProject.props" />
 
     <PropertyGroup>

TUnit/TUnit.props

@@ -7,7 +7,6 @@
         <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
         <TestingPlatformShowTestsFailure>true</TestingPlatformShowTestsFailure>
         <TestingPlatformCaptureOutput>false</TestingPlatformCaptureOutput>
-        <LangVersion>latest</LangVersion>
         <OutputType>Exe</OutputType>
     </PropertyGroup>
 

TUnit/TUnit.targets

@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
 
+    <PropertyGroup>
+        <LangVersion Condition="'$(LangVersion)' == ''">latest</LangVersion>
+    </PropertyGroup>
+
     <ItemGroup Condition="'$(TUnitImplicitUsings)' == 'true'">
         <Using Include="TUnit.Core" />
         <Using Include="TUnit.Core.HookType" Static="True" />