NestJS | tRPC

@trpc12/nest serves a contract from Nest controllers. @experimental_Implement(contract) adds the Nest route for the contract's REST mapping; the method returns the procedure, so the controller's injected services reach the resolver through this. The package is experimental, so its values are named experimental_* until it's promoted.
import { function experimental_Implement(contract: object): (target: object, propertyKey: string | symbol, descriptor: PropertyDescriptor) => voidexperimental_Implement, class experimental_TrpcModuleexperimental_TrpcModule } from '@trpc12/nest';

const const impl: ImplementResult<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, {
    post: {
        byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
            meta: {
                route?: Route | undefined;
            };
        }>, {
            inputIn: {
                id: string;
            };
            inputOut: {
                id: string;
            };
            errors: InputValidationError<{
                readonly code: "invalid_type";
                readonly expected: z.core.$ZodInvalidTypeExpected;
                readonly path: readonly [] | readonly ["id"];
                readonly message: string;
            } | {
                readonly code: "too_big";
                readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
                ... 4 more ...;
                readonly message: string;
            } | ... 9 more ... | {
                ...;
            }>;
            requires: never;
        }>, {
            ...;
        }>, {
            ...;
        }>>;
    };
}>impl = const t: TrpcRoot<{
    user: User | null;
}, {
    route?: Route | undefined;
}, ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>>t.TrpcRoot<{ user: User | null; }, { route?: Route | undefined; }, ExtendedDef<RootDef<{ user: User | null; }, {}>, RootDef<{}, OpenApiMeta>>>.implement<{
    post: {
        byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
            meta: {
                route?: Route | undefined;
            };
        }>, {
            inputIn: {
                id: string;
            };
            inputOut: {
                id: string;
            };
            errors: InputValidationError<{
                readonly code: "invalid_type";
                readonly expected: z.core.$ZodInvalidTypeExpected;
                readonly path: readonly [] | readonly ["id"];
                readonly message: string;
            } | {
                readonly code: "too_big";
                readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
                readonly maximum: string | number;
                readonly inclusive?: boolean | undefined;
                readonly exact?: boolean | undefined;
                readonly path: readonly [] | readonly [...];
                readonly message: string;
            } | ... 9 more ... | {
                ...;
            }>;
            requires: never;
        }>, {
            ...;
        }>, {
            ...;
        }>>;
    };
}>(contract: {
    post: {
        byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
            meta: {
                route?: Route | undefined;
            };
        }>, {
            inputIn: {
                id: string;
            };
            inputOut: {
                id: string;
            };
            errors: InputValidationError<{
                readonly code: "invalid_type";
                readonly expected: z.core.$ZodInvalidTypeExpected;
                readonly path: readonly [] | readonly ["id"];
                readonly message: string;
            } | {
                readonly code: "too_big";
                readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
                readonly maximum: string | number;
                readonly inclusive?: boolean | undefined;
                readonly exact?: boolean | undefined;
                readonly path: readonly [] | readonly [...];
                readonly message: string;
            } | ... 9 more ... | {
                ...;
            }>;
            requires: never;
        }>, {
            ...;
        }>, {
            ...;
        }>>;
    };
}): ImplementResult<...>implement(const appContract: {
    post: {
        byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
            meta: {
                route?: Route | undefined;
            };
        }>, {
            inputIn: {
                id: string;
            };
            inputOut: {
                id: string;
            };
            errors: InputValidationError<{
                readonly code: "invalid_type";
                readonly expected: z.core.$ZodInvalidTypeExpected;
                readonly path: readonly [] | readonly ["id"];
                readonly message: string;
            } | {
                readonly code: "too_big";
                readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
                ... 4 more ...;
                readonly message: string;
            } | ... 9 more ... | {
                ...;
            }>;
            requires: never;
        }>, {
            ...;
        }>, {
            ...;
        }>>;
    };
}appContract);

@function Controller(): ClassDecorator (+2 overloads)Controller()
class class PostControllerPostController {
  constructor(@function Inject(token?: InjectionToken | ForwardReference): PropertyDecorator & ParameterDecoratorInject(class PostsPosts) private readonly PostController.posts: Postsposts: class PostsPosts) {}

  @function experimental_Implement(contract: object): (target: object, propertyKey: string | symbol, descriptor: PropertyDescriptor) => voidexperimental_Implement(const appContract: {
    post: {
        byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
            meta: {
                route?: Route | undefined;
            };
        }>, {
            inputIn: {
                id: string;
            };
            inputOut: {
                id: string;
            };
            errors: InputValidationError<{
                readonly code: "invalid_type";
                readonly expected: z.core.$ZodInvalidTypeExpected;
                readonly path: readonly [] | readonly ["id"];
                readonly message: string;
            } | {
                readonly code: "too_big";
                readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
                readonly maximum: string | number;
                readonly inclusive?: boolean | undefined;
                readonly exact?: boolean | undefined;
                readonly path: readonly [] | readonly [...];
                readonly message: string;
            } | ... 9 more ... | {
                ...;
            }>;
            requires: never;
        }>, {
            ...;
        }>, {
            ...;
        }>>;
    };
}appContract.post: {
    byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
        meta: {
            route?: Route | undefined;
        };
    }>, {
        inputIn: {
            id: string;
        };
        inputOut: {
            id: string;
        };
        errors: InputValidationError<{
            readonly code: "invalid_type";
            readonly expected: z.core.$ZodInvalidTypeExpected;
            readonly path: readonly [] | readonly ["id"];
            readonly message: string;
        } | {
            readonly code: "too_big";
            readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
            readonly maximum: string | number;
            readonly inclusive?: boolean | undefined;
            readonly exact?: boolean | undefined;
            readonly path: readonly [] | readonly [...];
            readonly message: string;
        } | ... 9 more ... | {
            ...;
        }>;
        requires: never;
    }>, {
        ...;
    }>, {
        ...;
    }>>;
}post.byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        readonly maximum: string | number;
        readonly inclusive?: boolean | undefined;
        readonly exact?: boolean | undefined;
        readonly path: readonly [] | readonly [...];
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>byId) // .meta({ route: { method: 'GET', path: '/posts/{id}' } })
  PostController.byId(): ImplementedProcedure<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        ... 4 more ...;
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>, ContractProcedure<...>, never>byId() {
    return const impl: ImplementResult<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, {
    post: {
        byId: ContractProcedure<"query", ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
            meta: {
                route?: Route | undefined;
            };
        }>, {
            inputIn: {
                id: string;
            };
            inputOut: {
                id: string;
            };
            errors: InputValidationError<{
                readonly code: "invalid_type";
                readonly expected: z.core.$ZodInvalidTypeExpected;
                readonly path: readonly [] | readonly ["id"];
                readonly message: string;
            } | {
                readonly code: "too_big";
                readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
                readonly maximum: string | number;
                readonly inclusive?: boolean | undefined;
                readonly exact?: boolean | undefined;
                readonly path: readonly [] | readonly [...];
                readonly message: string;
            } | ... 9 more ... | {
                ...;
            }>;
            requires: never;
        }>, {
            ...;
        }>, {
            ...;
        }>>;
    };
}>impl.post: {
    readonly byId: ProcedureImplementer<ImplementerDef<ExtendedDef<RootDef<{
        user: User | null;
    }, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
        meta: {
            route?: Route | undefined;
        };
    }>, {
        inputIn: {
            id: string;
        };
        inputOut: {
            id: string;
        };
        errors: InputValidationError<{
            readonly code: "invalid_type";
            readonly expected: z.core.$ZodInvalidTypeExpected;
            readonly path: readonly [] | readonly ["id"];
            readonly message: string;
        } | {
            readonly code: "too_big";
            readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
            readonly maximum: string | number;
            readonly inclusive?: boolean | undefined;
            readonly exact?: boolean | undefined;
            readonly path: readonly [] | readonly [...];
            readonly message: string;
        } | ... 9 more ... | {
            ...;
        }>;
        requires: never;
    }>, {
        ...;
    }>, {
        ...;
    }>>, ContractProcedure<...>>;
}post.byId: ProcedureImplementer<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        readonly maximum: string | number;
        readonly inclusive?: boolean | undefined;
        readonly exact?: boolean | undefined;
        readonly path: readonly [] | readonly [...];
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>, ContractProcedure<...>>byId.query: <TrpcError<"NOT_FOUND", {
    id: string;
}> | Post>(resolver: (opts: ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        ... 5 more ...;
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>>) => (TrpcError<...> | Post) & (MaybePromise<...> | Effect<...>)) => ImplementedProcedure<...>query(
      (opts: ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        readonly maximum: string | number;
        readonly inclusive?: boolean | undefined;
        readonly exact?: boolean | undefined;
        readonly path: readonly [] | readonly [...];
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>>opts) =>
        this.PostController.posts: Postsposts.Posts.find(id: string): Post | undefinedfind(opts: ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        readonly maximum: string | number;
        readonly inclusive?: boolean | undefined;
        readonly exact?: boolean | undefined;
        readonly path: readonly [] | readonly [...];
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>>opts.ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{ user: User | null; }, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, { ...; }>, { ...; }>, { ...; }>, { ...; }>>>.input: {
    id: string;
}input.id: stringid) ??
        opts: ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        readonly maximum: string | number;
        readonly inclusive?: boolean | undefined;
        readonly exact?: boolean | undefined;
        readonly path: readonly [] | readonly [...];
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>>opts.ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{ user: User | null; }, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, { ...; }>, { ...; }>, { ...; }>, { ...; }>>>.errors: ErrorConstructors<{
    NOT_FOUND: TrpcError<"NOT_FOUND", {
        id: string;
    }>;
}>errors.type NOT_FOUND: (opts: ErrorConstructorOpts<{
    id: string;
}>) => TrpcError<"NOT_FOUND", {
    id: string;
}>NOT_FOUND({ data: {
    id: string;
}data: { id: stringid: opts: ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{
    user: User | null;
}, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, {
    meta: {
        route?: Route | undefined;
    };
}>, {
    inputIn: {
        id: string;
    };
    inputOut: {
        id: string;
    };
    errors: InputValidationError<{
        readonly code: "invalid_type";
        readonly expected: z.core.$ZodInvalidTypeExpected;
        readonly path: readonly [] | readonly ["id"];
        readonly message: string;
    } | {
        readonly code: "too_big";
        readonly origin: "number" | "int" | "bigint" | "date" | "string" | "array" | "set" | "file" | (string & {});
        readonly maximum: string | number;
        readonly inclusive?: boolean | undefined;
        readonly exact?: boolean | undefined;
        readonly path: readonly [] | readonly [...];
        readonly message: string;
    } | ... 9 more ... | {
        ...;
    }>;
    requires: never;
}>, {
    ...;
}>, {
    ...;
}>>>opts.ResolverOpts<ImplementerDef<ExtendedDef<RootDef<{ user: User | null; }, {}>, RootDef<{}, OpenApiMeta>>, ContractWith<ContractWith<ContractWith<ContractWith<ContractRootDef<{}>, { ...; }>, { ...; }>, { ...; }>, { ...; }>>>.input: {
    id: string;
}input.id: stringid } }),
    );
  }
}

@function Module(metadata: ModuleMetadata): ClassDecoratorModule({
  ModuleMetadata.imports?: (Type<any> | ForwardReference<any> | DynamicModule | Promise<DynamicModule>)[] | undefinedimports: [
    class experimental_TrpcModuleexperimental_TrpcModule.experimental_TrpcModule.forRoot(options?: TrpcModuleOptions): DynamicModuleforRoot({
      TrpcModuleOptions.createContext?: ((opts: CreateContextOpts<ExecutionContext>) => object | Promise<object>) | undefinedcreateContext: (opts: CreateContextOpts<ExecutionContext>opts) => ({
        user: anyuser: opts: CreateContextOpts<ExecutionContext>opts.CreateContextOpts<ExecutionContext>.platform: ExecutionContextplatform.ArgumentsHost.switchToHttp(): HttpArgumentsHostswitchToHttp().HttpArgumentsHost.getRequest<any>(): anygetRequest().user,
      }),
      TrpcModuleOptions.layer?: Layer.Layer<any, any, never> | undefinedlayer: class DbDb.Db.layer: Layer.Layer<Db, never, never>layer,
    }),
  ],
  ModuleMetadata.controllers?: Type<any>[] | undefinedcontrollers: [class PostControllerPostController],
  ModuleMetadata.providers?: Provider[] | undefinedproviders: [class PostsPosts],
})
class class AppModuleAppModule {}
A leaf needs a route path, .meta({ route: { path } }). Pass a contract router instead and return impl.router({ … }) (or a plain object of procedures) to get default paths from the keys below it (/post/byId).
experimental_TrpcModule.forRoot() takes the OpenAPI handler's options; createContext's platform is Nest's ExecutionContext. forRootAsync({ inject, useFactory }) builds them from providers. One handler serves every route, so the layer is built once and released on shutdown (app.enableShutdownHooks() or app.close()).
Guards, pipes and filters run as usual; put @experimental_Implement above the method's other decorators so they apply to every route it adds. The procedure's own middleware and validation run after them, and errors use the REST shape above.
Bodies Nest's JSON and urlencoded parsers read are used as parsed; others are read from the request.
Express only. Nest needs experimentalDecorators.
Routes and errors follow the OpenAPI handler.