We’re pleased to introduce the first preview of Source Generators, a new C# compiler feature that lets C# developers inspect user code and generate new C# source files that can be added to a compilation. This is done via a new kind of component that we’re calling a Source Generator.
To get started with Source Generators, you’ll need to install the latest .NET 5 preview and the latest Visual Studio preview. Note: to build a source generator, you currently require Visual Studio. This will change in the next .NET 5 preview.
What is a Source Generator?
Unless you’ve been closely following every prototype and proposal related to the C# language and compiler, then there’s a good chance you’re asking, “What is a Source Generator” right now. A Source Generator is a piece of code that runs during compilation and can inspect your program to produce additional files that are compiled together with the rest of your code.
A Source Generator is a new kind of component that C# developers can write that lets you do two major things:
- Retrieve a Compilation object that represents all user code that is being compiled. This object can be inspected and you can write code that works with the syntax and semantic models for the code being compiled, just like with analyzers today.
- Generate C# source files that can be added to a Compilation object during the course of compilation. In other words, you can provide additional source code as input to a compilation while the code is being compiled.
When combined, these two things are what make Source Generators so useful. You can inspect user code with all of the rich metadata that the compiler builds up during compilation, then emit C# code back into the same compilation that is based on the data you’ve analyzed! If you’re familiar with Roslyn Analyzers, you can think of Source Generators as analyzers that can emit C# source code.
Source generators run as a phase of compilation visualized below: