Roslyn: The .NET Compiler Platform

Roslyn is the .NET Compiler Platform: the open-source compiler for C# and Visual Basic that exposes its own internals, syntax trees, semantic models, and diagnostic pipeline, as an API rather than a black box. That exposure is what makes source generators, analyzers, and code fix providers possible in the first place.

The articles in this collection cover Roslyn from the perspective of people building on it: incremental source generator pipelines, custom analyzer rules, MSBuild integration for multi-targeted analyzer packages, and the pitfalls that only show up once you multi-target several Roslyn API versions or share tooling across Visual Studio’s MEF composition.

My Analyzer Shipped Without Checking Its Own Source

NetEvolve.Analyzer enforces null-check idioms and file organization on other people’s code, but had never run against its own. Fixing that surfaced 39 warnings, a silent Visual Studio MEF failure, and a follow-up NE0008 bug where DateOnly and TimeOnly got flagged blind to which target framework actually has them, the same multi-targeting blindness in a different corner of the codebase.

Incremental Source Generators Done Right: Ship It Without Breaking Consumers

Packaging Generators

Parts 1 through 3 of this series made the generator correct, incremental, and proven by tests. None of it reaches a single consumer if the NuGet package is laid out wrong — and the failure modes are silent: a DLL in lib/ instead of analyzers/dotnet/cs simply never loads, a missing dependency throws only inside the compiler, and a marker attribute delivered carelessly breaks InternalsVisibleTo in ways users cannot diagnose. This final part covers the packaging contract: the netstandard2.0 rule, the package layout, dependency bundling, attribute delivery, debugging the shipped bits, and the analyzer hygiene rules that keep you honest.

Prove the Cache Hits

You followed the equality rules, you shaped the pipeline correctly, and your generator still might be re-running on every keystroke — because nobody ever asked the driver. Roslyn records exactly why each pipeline step re-executed, and you can assert against those reasons in a plain xUnit test. This is the test that turns “my generator is incremental” from a claim into a regression-protected fact, plus the catalog of anti-patterns it catches in the wild.

Pipeline Patterns

Part 1 of this series established the equality contract: every value flowing through an incremental generator pipeline must be comparable by value, or the cache misses and the generator re-runs on every keystroke. This part is about the pipeline itself — ForAttributeWithMetadataName as the entry point, where to filter, where to transform, how to combine providers without accidentally subscribing to the entire Compilation, and the Collect trap that silently breaks everything you fixed in part 1. It ends with a complete worked generator you can steal.

The Equality Contract

IIncrementalGenerator exists for one reason: to run only when its inputs actually change. Most generators fail at exactly that, because somewhere in the pipeline a value is compared by reference and the cache silently misses. This is part 1 of a 4-part series on getting incrementalism right, and it starts where every broken generator starts: the equality contract, the ImmutableArray trap, and the EquatableArray that fixes it.