perf(build): trim test TFMs and skip viewer dump by default

.github/CONTRIBUTING.md

@@ -104,6 +104,38 @@ The relevant files are at `docs > docs > tutorials-[basics|extras|assertions]`
 
 If want to provide sample code for complicated or useful different test suite set-ups, that's also very welcome, as this can help other users get started a lot quicker!
 
+## Building TUnit Locally
+
+TUnit ships several solution files. Pick the right one for your task — the
+full `TUnit.slnx` is large enough that a cold build can take 20+ minutes,
+which is rarely what contributors actually need:
+
+| Solution         | Projects | When to use                                                                                                    |
+| ---------------- | -------- | -------------------------------------------------------------------------------------------------------------- |
+| `TUnit.Dev.slnx` | 44       | **Recommended for contributors.** Drops the per-Roslyn-version generator variants and example projects. Open this in Visual Studio / Rider for day-to-day work. |
+| `TUnit.CI.slnx`  | 73       | What CI builds. Use only when you're verifying CI-specific changes.                                            |
+| `TUnit.slnx`     | 96       | Full shipping graph including all per-Roslyn-version analyzer/generator variants. Slow; rarely needed locally. |
+
+### Faster repeat builds
+
+Set `MSBUILDUSESERVER=1` in your shell to keep the MSBuild process alive
+between invocations — significant speedup on warm/incremental builds.
+
+```bash
+export MSBUILDUSESERVER=1   # bash/zsh
+$env:MSBUILDUSESERVER = '1' # PowerShell
+```
+
+### Inspecting generated source
+
+Source-generated files are not written to disk by default (saves significant
+disk I/O on every build). To dump them under each test project's
+`SourceGeneratedViewer\` folder, build with:
+
+```bash
+dotnet build -p:EmitCompilerGeneratedFiles=true
+```
+
 ### Code Contributions
 
 When contributing code to TUnit, please keep these important requirements in mind:

Library.props

@@ -4,7 +4,9 @@
 
         <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
 
-        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <!-- XML doc generation is only needed when producing NuGet packages or running on CI.
+             Skipping it on local incremental builds saves 3-8% Roslyn time per TFM. -->
+        <GenerateDocumentationFile Condition="'$(IsPacking)' == 'true' or '$(GeneratePackageOnBuild)' == 'true' or '$(ContinuousIntegrationBuild)' == 'true'">true</GenerateDocumentationFile>
         <!-- Suppress XML doc warnings — not all public APIs are documented yet,
              and some existing comments have minor formatting issues -->
         <NoWarn>$(NoWarn);CS1591;CS1570;CS1572;CS1573;CS1574;CS1584;CS1587;CS1658;CS1734;CS0419</NoWarn>

TUnit.Assertions.SourceGenerator.Tests/TUnit.Assertions.SourceGenerator.Tests.csproj

@@ -1,5 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+  <PropertyGroup>
+    <!-- Multi-target to verify generator output across consumer TFMs (snapshot tests). -->
+    <TargetFrameworks>net472;net8.0;net9.0;net10.0</TargetFrameworks>
+  </PropertyGroup>
+
   <Import Project="..\TestProject.props" />
 
   <PropertyGroup>

TUnit.Core.SourceGenerator.Tests/TUnit.Core.SourceGenerator.Tests.csproj

@@ -1,5 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+  <PropertyGroup>
+    <!-- Multi-target to verify generator output across consumer TFMs (snapshot tests). -->
+    <TargetFrameworks>net472;net8.0;net9.0;net10.0</TargetFrameworks>
+  </PropertyGroup>
+
   <Import Project="..\TestProject.props" />
 
   <PropertyGroup>

TUnit.PublicAPI/TUnit.PublicAPI.csproj

@@ -1,7 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+    <PropertyGroup>
+        <!-- Multi-target so public API snapshots cover every supported consumer TFM. -->
+        <TargetFrameworks>net472;net8.0;net9.0;net10.0</TargetFrameworks>
+    </PropertyGroup>
+
   <Import Project="..\TestProject.props" />
-    
+
     <PropertyGroup>
         <Configuration>Release</Configuration>
     </PropertyGroup>

TUnit.slnx

@@ -101,7 +101,6 @@
 
   <!-- Examples and playground projects -->
   <Folder Name="/Examples/">
-    <Project Path="Playground/Playground.csproj" />
     <Project Path="TUnit.Example.Asp.Net/TUnit.Example.Asp.Net.csproj" />
     <Project Path="TUnit.Example.Asp.Net.TestProject/TUnit.Example.Asp.Net.TestProject.csproj" />
     <Project Path="TUnit.Example.FsCheck.TestProject/TUnit.Example.FsCheck.TestProject.csproj" />

TestProject.props

@@ -9,7 +9,11 @@
         Condition="'$(MSBuildProjectExtension)' == '.fsproj'" />
 
     <PropertyGroup>
-        <TargetFrameworks>net472;net8.0;net9.0;net10.0</TargetFrameworks>
+        <!-- Default test projects to net10.0 only. Multi-targeting (net472;net8;net9) is
+             expensive (4x compile work) and only matters for projects that snapshot output
+             across consumer TFMs (e.g. TUnit.PublicAPI, TUnit.Core.SourceGenerator.Tests).
+             Those projects set <TargetFrameworks> explicitly before this import. -->
+        <TargetFrameworks Condition="'$(TargetFrameworks)' == '' and '$(TargetFramework)' == ''">net10.0</TargetFrameworks>
 
         <OutputType>Exe</OutputType>
 
@@ -25,24 +29,35 @@
 
     </PropertyGroup>
 
-    <Target Name="CleanSourceGeneratedViewer" BeforeTargets="BeforeBuild"
-            Condition="'$(ContinuousIntegrationBuild)' != 'true' AND Exists('$(ProjectDir)SourceGeneratedViewer')">
-        <ItemGroup>
-            <FilesToDelete Include="$(ProjectDir)SourceGeneratedViewer\**\*" />
-        </ItemGroup>
-        <Delete Files="@(FilesToDelete)" ContinueOnError="true" />
-    </Target>
-
+    <!-- Default off: emitting generator output to disk costs significant I/O per build. -->
     <PropertyGroup>
-        <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
-        <CompilerGeneratedFilesOutputPath>SourceGeneratedViewer</CompilerGeneratedFilesOutputPath>
+        <EmitCompilerGeneratedFiles Condition="'$(EmitCompilerGeneratedFiles)' == ''">false</EmitCompilerGeneratedFiles>
+        <CompilerGeneratedFilesOutputPath Condition="'$(EmitCompilerGeneratedFiles)' == 'true'">SourceGeneratedViewer</CompilerGeneratedFilesOutputPath>
     </PropertyGroup>
 
+    <!-- Compile Remove must stay unconditional: a stale folder from a previous opt-in build
+         would otherwise be picked up by the implicit C# glob and produce CS0111 / CS0579
+         duplicate-member errors alongside the in-memory generator output. -->
     <ItemGroup>
         <Compile Remove="SourceGeneratedViewer\**" />
+    </ItemGroup>
+
+    <ItemGroup Condition="'$(EmitCompilerGeneratedFiles)' == 'true'">
         <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. -->
+    <Target Name="CleanSourceGeneratedViewer" BeforeTargets="BeforeBuild"
+            Condition="'$(ContinuousIntegrationBuild)' != 'true' AND Exists('$(ProjectDir)SourceGeneratedViewer')">
+        <ItemGroup>
+            <FilesToDelete Include="$(ProjectDir)SourceGeneratedViewer\**\*" />
+        </ItemGroup>
+        <Delete Files="@(FilesToDelete)" ContinueOnError="true" />
+    </Target>
+
     <!-- Enable VSCode test discovery integration -->
     <ItemGroup>
         <PackageReference Include="Microsoft.Testing.Platform.MSBuild" />