A comprehensive guide to building a VS Code-style extension system in C# (.NET 8/9). Covers the four core concepts: extension manifests (strongly-typed records backed by extension.json), contribution points (generic typed registration hooks), lazy activation events (deferred loading triggered by host-fired events), and a scoped IExtensionContext API surface that limits what extensions can access. Includes full code for ExtensionManifest, ExtensionPointRegistry, ExtensionActivator, ExtensionHost, and a folder-scan ExtensionRegistry with version conflict resolution. Also addresses key tradeoffs: in-process vs. out-of-process isolation, when this pattern is overkill vs. appropriate, and production concerns like AssemblyLoadContext for isolation and SemVer parsing.
Table of contents
What Makes VS Code's Extension Model So Powerful?Extension Manifests in C#Defining Extension Points (Contribution Points)Lazy Activation with Activation EventsThe Host API Surface: What Extensions Can AccessExtension Registry and Marketplace PatternPutting It Together: A Complete Extension SystemHow This Compares to VS Code's Real Extension APIFrequently Asked QuestionsWrapping UpSort: