Add playground environment for end-to-end testing

.gitignore

@@ -148,4 +148,7 @@ L10N.Integrations/phantom*
 tools/
 
 # VS Code settings
-.vscode/mcp.json
+.vscode/mcp.json
+
+# Auto-generated package version file for playground
+src/ReferenceCop.Package/package-version.txt

playground/.gitignore

@@ -0,0 +1,3 @@
+# Standard .NET ignores for the test projects
+**/bin/
+**/obj/

playground/README.md

@@ -0,0 +1,43 @@
+# ReferenceCop Playground
+
+This is a playground environment for testing ReferenceCop changes end-to-end.
+
+## Structure
+
+- `TestProject/` - Sample project that uses ReferenceCop for validation
+  - `SampleApp/` - Sample application project
+  - `SampleLibrary/` - Sample library project
+  - `nuget.config` - Configured to use ReferenceCop package from build output
+  - `Directory.Build.props` - Centralized ReferenceCop package reference with auto-version detection
+
+## Workflow
+
+1. **Make changes** to ReferenceCop source code
+2. **Build and pack** the ReferenceCop package:
+   ```powershell
+   cd ..\src\ReferenceCop.Package
+   dotnet pack -c Debug
+   ```
+   This automatically writes the package version to `package-version.txt`
+3. **Restore and build** the test project:
+   ```powershell
+   cd playground\TestProject\SampleApp
+   dotnet restore
+   dotnet build
+   ```
+4. **Introduce test violations** or modify the `ReferenceCop.config` to test your changes
+
+**Note**: 
+- The `nuget.config` uses the package directly from the build output directory (`../../src/ReferenceCop.Package/bin/Debug`)
+- The package version is automatically read from `package-version.txt` via `Directory.Build.props`
+- No manual version updates needed!
+
+## Testing Different Rule Types
+
+The `ReferenceCop.config` includes examples of all three rule types:
+
+1. **AssemblyName** - Blocks references to assemblies matching a pattern
+2. **ProjectTag** - Blocks references between projects with specific tags
+3. **ProjectPath** - Blocks references based on project folder paths
+
+Modify the rules or project references to test violations.

playground/TestProject/Directory.Build.props

@@ -0,0 +1,33 @@
+<Project>
+
+  <PropertyGroup>
+    <!-- ReferenceCopRepositoryRoot as required by ReferenceCop -->
+    <ReferenceCopRepositoryRoot>$(MSBuildThisFileDirectory)</ReferenceCopRepositoryRoot>
+
+    <!-- 
+      Read the package version from the file written during pack
+      Falls back to a default version if file doesn't exist
+    -->
+    <PlaygroundVersionFile>$(MSBuildThisFileDirectory)..\..\src\ReferenceCop.Package\package-version.txt</PlaygroundVersionFile>
+    <ReferenceCopVersion Condition="Exists('$(PlaygroundVersionFile)')">$([System.IO.File]::ReadAllText('$(PlaygroundVersionFile)').Trim())</ReferenceCopVersion>
+    <ReferenceCopVersion Condition="'$(ReferenceCopVersion)' == ''">20241220.000000</ReferenceCopVersion>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <!-- 
+      ReferenceCop package reference applied to all projects in the playground
+      Version is automatically read from package-version.txt after pack
+      The version format for Debug builds is: yyyyMMdd.hhmmss
+    -->
+    <PackageReference Include="ReferenceCop.Dev" Version="$(ReferenceCopVersion)">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+
+    <!-- ReferenceCop.config as AdditionalFile with required Label -->
+    <AdditionalFiles Include="$(MSBuildThisFileDirectory)ReferenceCop.config">
+      <Label>ReferenceCopConfig</Label>
+    </AdditionalFiles>
+  </ItemGroup>
+
+</Project>

playground/TestProject/ReferenceCop.config

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+<?xml version="1.0" encoding="utf-8"?>
+<ReferenceCopConfig xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://raw.githubusercontent.com/mfogliatto/ReferenceCop/main/ReferenceCopConfig.xsd">
+  <Rules>
+    <!-- Example 1: Block references to assemblies matching a pattern -->
+    <AssemblyName>
+      <Name>NoSystemWebReferences</Name>
+      <Description>System.Web assemblies should not be referenced</Description>
+      <Severity>Error</Severity>
+      <Pattern>System.Web*</Pattern>
+    </AssemblyName>
+
+    <!-- Example 2: Block references between projects with specific tags -->
+    <ProjectTag>
+      <Name>AppCannotReferenceTools</Name>
+      <Description>Application projects should not reference tool projects</Description>
+      <Severity>Warning</Severity>
+      <FromProjectTag>App</FromProjectTag>
+      <ToProjectTag>Tools</ToProjectTag>
+    </ProjectTag>
+
+    <!-- Example 3: Block references based on project paths -->
+    <ProjectPath>
+      <Name>AppCannotReferenceInternal</Name>
+      <Description>Applications should not reference internal implementation libraries</Description>
+      <Severity>Error</Severity>
+      <FromPath>**/SampleApp/**</FromPath>
+      <ToPath>**/Internal/**</ToPath>
+    </ProjectPath>
+
+    <!-- Example 4: Another AssemblyName rule for testing -->
+    <AssemblyName>
+      <Name>NoNewtonsoftJson</Name>
+      <Description>Use System.Text.Json instead of Newtonsoft.Json</Description>
+      <Severity>Warning</Severity>
+      <Pattern>Newtonsoft.Json*</Pattern>
+    </AssemblyName>
+  </Rules>
+</ReferenceCopConfig>

playground/TestProject/SampleApp/Program.cs

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+using SampleLibrary;
+
+namespace SampleApp;
+
+/// <summary>
+/// Sample application to test ReferenceCop.
+/// </summary>
+public class Program
+{
+    public static void Main(string[] args)
+    {
+        Console.WriteLine("ReferenceCop Playground Test Application");
+        Console.WriteLine("=========================================");
+
+        var calculator = new Calculator();
+
+        Console.WriteLine($"5 + 3 = {calculator.Add(5, 3)}");
+        Console.WriteLine($"10 - 4 = {calculator.Subtract(10, 4)}");
+        Console.WriteLine($"6 * 7 = {calculator.Multiply(6, 7)}");
+        Console.WriteLine($"20 / 5 = {calculator.Divide(20, 5)}");
+
+        Console.WriteLine("\nTest completed successfully!");
+
+        // Uncomment to test violation detection:
+        // 1. Add a PackageReference to Newtonsoft.Json in the .csproj
+        // 2. Add: using Newtonsoft.Json;
+        // 3. Build to see the warning
+    }
+}

playground/TestProject/SampleApp/SampleApp.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <ProjectTag>App</ProjectTag>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\SampleLibrary\SampleLibrary.csproj" />
+  </ItemGroup>
+
+</Project>

playground/TestProject/SampleLibrary/Calculator.cs

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+namespace SampleLibrary;
+
+/// <summary>
+/// A simple calculator class for demonstration.
+/// </summary>
+public class Calculator
+{
+    public int Add(int a, int b) => a + b;
+
+    public int Subtract(int a, int b) => a - b;
+
+    public int Multiply(int a, int b) => a * b;
+
+    public int Divide(int a, int b)
+    {
+        if (b == 0)
+        {
+            throw new DivideByZeroException("Cannot divide by zero");
+        }
+
+        return a / b;
+    }
+}

playground/TestProject/SampleLibrary/SampleLibrary.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <!-- Tag this project as a library -->
+    <ProjectTag>Library</ProjectTag>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
+  </ItemGroup>
+
+</Project>

playground/TestProject/nuget.config

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <!-- Direct reference to ReferenceCop package build output -->
+    <add key="local-build" value="../../src/ReferenceCop.Package/bin/Debug" />
+    <!-- NuGet.org for other dependencies -->
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
+  </packageSources>
+</configuration>

src/ReferenceCop.Package/ReferenceCop.Package.csproj

@@ -58,4 +58,13 @@
     </ItemGroup>
   </Target>
 
+  <!-- Write package version to file for playground offline dev feed -->
+  <Target Name="_WritePackageVersionForPlaygroundOfflineDevFeed" AfterTargets="Pack" Condition="'$(IsDevEnvironment)' == 'true'">
+    <PropertyGroup>
+      <VersionFile>$(MSBuildThisFileDirectory)package-version.txt</VersionFile>
+    </PropertyGroup>
+    <WriteLinesToFile File="$(VersionFile)" Lines="$(PackageVersion)" Overwrite="true" />
+    <Message Text="Wrote package version $(PackageVersion) to $(VersionFile)" Importance="high" />
+  </Target>
+
 </Project>