The .NET Compiler Platform SDK

Compilers build a detailed model of application code as they validate the syntax and semantics of that code. They use this model to build the executable output from the source code. The .NET Compiler Platform SDK provides access to this model. Increasingly, we rely on integrated development environment (IDE) features such as IntelliSense, refactoring, intelligent rename, "Find all references," and "Go to definition" to increase our productivity. We rely on code analysis tools to improve our code quality, and code generators to aid in application construction. As these tools get smarter, they need access to more and more of the model that only compilers create as they process application code. This is the core mission of the Roslyn APIs: opening up the opaque boxes and allowing tools and end users to share in the wealth of information compilers have about our code. Instead of being opaque source-code-in and object-code-out translators, through Roslyn, compilers become platforms: APIs that you can use for code-related tasks in your tools and applications.

The .NET Compiler Platform SDK dramatically lowers the barrier to entry for creating code focused tools and applications. It creates many opportunities for innovation in areas such as meta-programming, code generation and transformation, interactive use of the C# and Visual Basic languages, and embedding of C# and Visual Basic in domain-specific languages.

The .NET Compiler Platform SDK enables you to build analyzers and code fixes that find and correct coding mistakes. Analyzers understand the syntax (structure of code) and semantics to detect practices that should be corrected. Code fixes provide one or more suggested fixes for addressing coding mistakes found by analyzers or compiler diagnostics. Typically, an analyzer and the associated code fixes are packaged together in a single project.

Analyzers and code fixes use static analysis to understand code. They do not run the code or provide other testing benefits. They can, however, point out practices that often lead to bugs, unmaintainable code, or standard guideline violation.

In addition to analyzers and code fixes, The .NET Compiler Platform SDK also enables you to build code refactorings. It also provides a single set of APIs that enable you to examine and understand a C# or Visual Basic codebase. Because you can use this single codebase, you can write analyzers and code fixes more easily by leveraging the syntactic and semantic analysis APIs provided by the .NET Compiler Platform SDK. Freed from the large task of replicating the analysis done by the compiler, you can concentrate on the more focused task of finding and fixing common coding errors for your project or library.

A smaller benefit is that your analyzers and code fixes are smaller and use much less memory when loaded in Visual Studio than they would if you wrote your own codebase to understand the code in a project. By leveraging the same classes used by the compiler and Visual Studio, you can create your own static analysis tools. This means your team can use analyzers and code fixes without a noticeable impact on the IDE's performance.

There are three main scenarios for writing analyzers and code fixes:

1. Enforce team coding standards
2. Provide guidance with library packages
3. Provide general guidance

Many teams have coding standards that are enforced through code reviews with other team members. Analyzers and code fixes can make this process much more efficient. Code reviews happen when a developer shares their work with others on the team. The developer will have invested all the time needed to complete a new feature before getting any comments. Weeks may go by while the developer reinforces habits that don't match the team's practices.

Analyzers run as a developer writes code. The developer gets immediate feedback that encourages following the guidance immediately. The developer builds habits to write compliant code as soon as they begin prototyping. When the feature is ready for humans to review, all the standard guidance has been enforced.

Teams can build analyzers and code fixes that look for the most common practices that violate team coding practices. These can be installed on each developer's machine to enforce the standards.

There is a wealth of libraries available for .NET developers on NuGet. Some of these come from Microsoft, some from third-party companies, and others from community members and volunteers. These libraries get more adoption and higher reviews when developers can succeed with those libraries.

In addition to providing documentation, you can provide analyzers and code fixes that find and correct common mis-uses of your library. These immediate corrections will help developers succeed more quickly.

You can package analyzers and code fixes with your library on NuGet. In that scenario, every developer who installs your NuGet package will also install the analyzer package. All developers using your library will immediately get guidance from your team in the form of immediate feedback on mistakes and suggested corrections.

The .NET developer community has discovered, through experience, patterns that work well and patterns that are best avoided. Several community members have created analyzers that enforce those recommended patterns. As we learn more, there is always room for new ideas.

These analyzers can be uploaded to the Visual Studio Marketplace and downloaded by developers using Visual Studio. Newcomers to the language and the platform learn accepted practices quickly and become productive earlier in their .NET journey. As these become more widely used, the community adopts these practices.

Source generators aim to enable compile time metaprogramming, that is, code that can be created at compile time and added to the compilation. Source generators are able to read the contents of the compilation before running, as well as access any additional files. This ability enables them to introspect both user C# code and generator-specific files. You can learn how to build incremental source generators using the source generator cookbook.

The .NET Compiler Platform SDK includes the latest language object models for code generation, analysis, and refactoring. This section provides a conceptual overview of the .NET Compiler Platform SDK. Further details can be found in the quickstarts, samples, and tutorials sections.

You can learn more about the concepts in the .NET Compiler Platform SDK in these five topics:

• Explore code with the syntax visualizer
• Understand the compiler API model
• Work with syntax
• Work with semantics
• Work with a workspace

To get started, you'll need to install the .NET Compiler Platform SDK:

There are two different ways to find the .NET Compiler Platform SDK in the Visual Studio Installer:

The .NET Compiler Platform SDK is not automatically selected as part of the Visual Studio extension development workload. You must select it as an optional component.

1. Run Visual Studio Installer
2. Select Modify
3. Check the Visual Studio extension development workload.
4. Open the Visual Studio extension development node in the summary tree.
5. Check the box for .NET Compiler Platform SDK. You'll find it last under the optional components.

Optionally, you'll also want the DGML editor to display graphs in the visualizer:

1. Open the Individual components node in the summary tree.
2. Check the box for DGML editor

1. Run Visual Studio Installer
2. Select Modify
3. Select the Individual components tab
4. Check the box for .NET Compiler Platform SDK. You'll find it at the top under the Compilers, build tools, and runtimes section.

Optionally, you'll also want the DGML editor to display graphs in the visualizer:

1. Check the box for DGML editor. You'll find it under the Code tools section.