Source Generators are the biggest paradigm shift in C# developer productivity. Instead of using slow Reflection at runtime to inspect your code, Source Generators allow you to write C# code that writes more C# code during compilation. This results in zero-overhead, lightning-fast execution.
In the past, to find all classes with a [Map] attribute, you used Reflection (Slow). Now, a Source Generator finds those attributes during your Build process and generates the mapping C# code for you. When you run the app, the code is already there, fully compiled.
Interceptors are an experimental but powerful feature that allows a Source Generator to "Hijack" a method call at compile time. If your code calls logger.Log(), an Interceptor can redirect that call to a highly-optimized, pre-compiled logging method instead.
By using the [JsonSerializable] source generator, the JSON serializer doesn't have to use Reflection to look at your properties. It generates a "Metadata class" that knows exactly where every byte is, making JSON parsing significantly faster and AOT (Ahead-of-Time) friendly.
Q: "How do Source Generators help with 'Native AOT' (Ahead-of-Time) compilation?"
Architect Answer: "Native AOT (compiling C# directly to a standalone exe like Go or Rust) forbids the use of Reflection because there is no 'Just-In-Time' compiler at runtime to resolve types. Source Generators are the savior of AOT. Because they generate the necessary logic during the build process, the resulting executable has no 'unknown' code paths. Every dependency is resolved and hard-coded before the app even leaves the CI/CD pipeline, allowing .NET apps to start in milliseconds and consume 50% less RAM."