Roslyn analyzers and ruleset files

Use Roslyn analyzers and ruleset files in Unity projects to inspect your code for style, quality, and other issues.

You can use existing analyzer libraries to inspect your code, as well as write your own analyzers to promote the best practices or conventions within your organization. This page explains how to use Roslyn analyzers in an empty Unity Project.

Using an existing Roslyn analyzer library

To use an existing Roslyn analyzer library, install the ErrorProne.NET.CoreAnalyzers library from NuGet inside your project. Then open the .csproj file. There are three .dll files included in the project as analyzers:

  <ItemGroup>
    <Analyzer Include="packages\ErrorProne.NET.CoreAnalyzers.0.1.2\analyzers\dotnet\cs\ErrorProne.NET.Core.dll" />
    <Analyzer Include="packages\ErrorProne.NET.CoreAnalyzers.0.1.2\analyzers\dotnet\cs\ErrorProne.Net.CoreAnalyzers.dll" />
    <Analyzer Include="packages\ErrorProne.NET.CoreAnalyzers.0.1.2\analyzers\dotnet\cs\RuntimeContracts.dll" />
  </ItemGroup>

Move the three .dll files into the Assets folder (or any folder nested in the Assets folder) in your Unity project. In the Editor, select the .dll file. In the Plugin Inspector, under Select platforms for plugin, disable Any Platform. Under Include platforms, disable Editor and Standalone platforms. Then, give all of the DLLs a new label called RoslynAnalyzer.

To test that everything works correctly, save a file named RethrowError.cs with the following code in your project’s Assets folder. This code causes ErrorProne.NET to raise warnings about incorrect exception propagation and suspicious exception handling:

using System;
using UnityEngine;

public class RethrowError : MonoBehaviour
{
    void Update()
    {
        try
        {
            DoSomethingInteresting();
        }
        catch (Exception e)
        {
            Debug.Log(e.Message);
            throw e;
        }
    }

    private void DoSomethingInteresting()
    {
        throw new System.NotImplementedException();
    }
}

Once you do this, you should see the following two warnings in the Console window:

Assets\RethrowError.cs(14,23): warning EPC12: Suspicious exception handling: only e.Message is observed in exception block.
Assets\RethrowError.cs(15,19): warning ERP021: Incorrect exception propagation. Use throw; instead.

Analyzer scope

Analyzers apply globally to any assembly in your project if they are in the Assets folder, or in a subfolder that does not contain an assembly definition file in any of their parent folders. If an analyzer is in a folder that contains an assembly definition, or a subfolder of such a folder, the analyzer only applies to the assembly generated from that assembly definition, and to any other assembly that references it.

This means that a package can supply analyzers that only apply to code that uses the package, for example to help guide package users to use the package API correctly.

Ruleset files

To define your own rules on how to handle the various warnings and errors that the analyzers in your project raise, you can create a ruleset file. For more information on how to create a custom ruleset, see Microsoft’s Visual Studio documentation on how to create a custom rule set.

In the Assets root folder, place a ruleset file named Default.ruleset. The rules you define in Default.ruleset apply to all predefined assemblies (for example Assembly-CSharp.dll), as well as all assemblies that are built using .asmdef files.

To override the rules in Default.ruleset for a predefined assembly, create a .ruleset file in the root folder with the name [PredefinedAssemblyName].ruleset. For example, the rules in Assembly-CSharp.ruleset apply to the code in Assembly-CSharp.dll. Only these .ruleset files are permitted inside the root folder:

• Default.ruleset
• Assembly-CSharp.ruleset
• Assembly-CSharp-firstpass.ruleset
• Assembly-CSharp-Editor.ruleset
• Assembly-CSharp-Editor-firstpass.ruleset

Workflow: Testing ruleset files in Unity

To test ruleset files in Unity, follow these steps:

Step 1: Set up the ruleset file

1. Create a subfolder named Subfolder inside your project’s Assets folder.
2. Inside Subfolder:
   1. Create a new .asmdef file.
   2. Save a duplicate copy of RethrowError.cs.
3. Create a Default.ruleset file inside Assets with the following code:

<?xml version="1.0" encoding="utf-8"?>
<RuleSet Name="New Rule Set" Description=" " ToolsVersion="10.0">
  <Rules AnalyzerId="ErrorProne.NET.CodeAnalyzers" RuleNamespace="ErrorProne.NET.CodeAnalyzers">
    <Rule Id="ERP021" Action="Error" />
  <Rule Id="EPC12" Action="None" />
  </Rules>
</RuleSet>

The Default.ruleset file defines the following rules:

• Suppress EPC12, the warning about suspicious exception handling.
• Elevate ERP021, the warning about incorrect exception propagation, to an error.

Step 2: Reload the project

After adding the ruleset files to your project, reimport any script that lives in an assembly where the rules should apply. This forces Unity to recompile the assembly using the new ruleset files. After recompilation, you should see two messages in the Console window:

Assets\Subfolder\RethrowError.cs(15,19): error ERP021: Incorrect exception propagation. Use throw; instead.
Assets\RethrowError.cs(15,19): error ERP021: Incorrect exception propagation. Use throw; instead.

Notice that Unity applies the rules defined in Default.ruleset to both Assets/RethrowError.cs and Assets/Subfolder/RethrowError.cs.

Step 3: Add a custom ruleset

In Assets/Subfolder, create a .ruleset file, and give it any name you like (in this exampleHello.ruleset):

<?xml version="1.0" encoding="utf-8"?>
<RuleSet Name="New Rule Set" Description=" " ToolsVersion="10.0">
  <Rules AnalyzerId="ErrorProne.NET.CodeAnalyzers" RuleNamespace="ErrorProne.NET.CodeAnalyzers">
    <Rule Id="ERP021" Action="Info" />
    <Rule Id="EPC12" Action="Info" />
  </Rules>
</RuleSet>

This new Hello.ruleset file tells Unity to print both EPC12 and ERP021 to the Console, without treating them as warnings or errors.

After Unity compiles the project again, you should see these messages in the Console window:

Assets\Subfolder\RethrowError.cs(14,23): info EPC12: Suspicious exception handling: only e.Message is observed in exception block.
Assets\Subfolder\RethrowError.cs(15,19): info ERP021: Incorrect exception propagation. Use throw; instead.
Assets\RethrowError.cs(15,19): error ERP021: Incorrect exception propagation. Use throw; instead.

The rules in Default.ruleset still apply to Assets\RethrowError.cs, but they no longer apply to Assets\Subfolder\RethrowError.cs, because the rules in Hello.ruleset override them.

For more information on all the allowed ruleset action files, see the Visual Studio documentation on Using the code analysis rule set editor.

More analyzers

The following are links to Github repositories of other popular Roslyn analyzer libraries:

• awesome-analyzers

• dotnet/roslyn-analyzers

• Added Roslyn analyzer compatibility in 2020.2 NewIn20202