feature: end-to-end type safety with native tRPC (trpc.io) integration

[jknack]

Overview

This PR introduces native, out-of-the-box support for the tRPC (trpc.io) protocol in Jooby.

Historically restricted to the Node.js/TypeScript ecosystem, this feature allows developers to write standard Java/Kotlin controllers and consume them directly in the browser using the official @trpc/client—complete with 100% type safety, autocomplete, and zero manual client generation.

Key Features & Implementation

• Annotation Processor (APT) Mapping:
  • Added @Trpc, @Trpc.Query, and @Trpc.Mutation annotations.
  • Automatically maps tRPC queries to HTTP GET and mutations to HTTP POST at the routing layer.
  • Seamlessly integrates with standard REST annotations (@POST, @PUT, @DELETE resolve as tRPC mutations).
  • Automatically unpacks multi-argument Java methods from tRPC JSON arrays (tuples) while safely ignoring framework-injected parameters like io.jooby.Context and Kotlin Continuation.
• TypeScript Generator (TrpcGenerator):
  • Custom engine wrapping typescript-generator to emit a strictly typed AppRouter and associated data models (DTOs).
  • Implemented a "reactive firewall" that deeply unwraps async types (CompletableFuture, Mono, Single, Uni, etc.) so internal JVM wrapper types never leak into the TypeScript definitions.
  • Generates a fully deterministic, alphabetically sorted trpc.d.ts file grouped by namespaces.
• Build Tooling:
  • Maven: Added TrpcMojo tied to the process-classes phase.
  • Gradle: Added TrpcTask to the jooby-gradle-plugin.
  • Supports configuration including custom type mappings, Jackson/JSON-B/Gson specific parsing, and Date/Enum formatting options.

Example

1. The Java Controller
Write standard Jooby controllers using the new @Trpc annotations.

import io.jooby.annotation.Trpc;

public record Movie(int id, String title, int year) {}

@Trpc("movies")
public class MovieService {

  @Trpc.Query
  public Movie getById(int id) {
    return new Movie(id, "Pulp Fiction", 1994);
  }

  @Trpc.Mutation
  public Movie create(Movie movie) {
    // save to database
    return movie;
  }
}

The Generated TypeScript (trpc.d.ts)

The build plugin automatically extracts the DTOs and generates the exact AppRouter shape expected by the frontend @trpc/client.

/* tslint:disable */
/* eslint-disable */

export interface Movie {
    id: number;
    title: string;
    year: number;
}

// --- tRPC Router Mapping ---

export type AppRouter = {
  movies: {
    // queries
    getById: { input: number; output: Movie };

    // mutations
    create: { input: Movie; output: Movie };
  };
};