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Prevent breaking changes using Microsoft.CodeAnalysis.PublicApiAnalyzers

For one of my clients, I maintain a set of libraries that help to streamline the development of new applications in .NET Core. The functionality offered through these libraries follow the 'paved road' principle and help the development teams to fall in the pit of success. They are used by multiple development teams working on different projects.

As a library author, I don’t have full control on all the different ways these libraries are used so I have to be very conscious in avoiding breaking changes. In this post I want to share some details on how I try to manage and avoid breaking changes.

Microsoft.CodeAnalysis.PublicApiAnalyzers

The ‘magic’ solution I use to avoid or handle breaking changes is with the help of a specific Roslyn analyzer, the Microsoft.CodeAnalysis.PublicApiAnalyzers.

Let me explain how this analyzer works.

First add a package reference to Microsoft.CodeAnalysis.PublicApiAnalyzers to your project:

dotnet add package Microsoft.CodeAnalysis.PublicAnalyzers

This will add 2 extra files to your project:

  • PublicAPI.Shipped.txt
  • PublicApi.Unshipped.txt

When you now try to build your project, you get a RS0016 diagnostics on all your public APIs:

This warning helps you to be aware that a change is done in a public api so that you can take it into account in code reviews and pull requests (or look at a way to avoid introducing a breaking change).

You can now use the code fix feature to add the API to the PublicAPI.Unshipped.txt file:

Remark: In Visual Studio, you can apply the fix in one go for all changes.

If I have changes in this file, I know that a made a breaking change somewhere. This allows me to track these breaking changes in an effective and centralized way. 

It is up to you as a library author when you release a new version of your library to copy the changes from the PublicAPI.Unshipped.txt file to the PublicAPI.Shipped.txt file.

Remark: While preparing this post, I stumbled over an alternative solution, PublicApiGenerator, mentioned in a blog post by Andrew Lock. If you have experience using this package, please let me now. 

More information

The paved road

NuGet Gallery | Microsoft.CodeAnalysis.PublicApiAnalyzers 3.3.4

Preventing breaking changes in public APIs with PublicApiGenerator

NuGet Gallery | PublicApiGenerator 11.3.0

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