NestJS server codegen

[aryobenholzner]

proposed solution for #11785

This is a prototype of a server code generator for NestJS. The code probably needs improvement, I'm relatively new in this codebase and tried to adhere to existing generators. As of now, I only want to gather feedback on the solution the generated output provides, and whether it's worth continuing this approach.

Description a per the added README

OpenApi Generator typescript-nestjs-server

Usage: The generated output is intended to be its own module, that can be imported into your NestJS App Module. You do not need to change generated files, just import the module and implement the API

Example usage (with the openapi sample petstore.yaml):

1. Invoke openapi-generator

   openapi-generator-cli.jar generate -i petstore.yaml -g typescript-nestjs-server -o api-module/
   

2. implement the contracts from api-module/api
handlers/PetService.ts:

   import { Pet, ApiResponse } from "models";
   import { Observable } from "rxjs";
   import { PetApi } from "../api";
   import { Inject, Injectable } from "@nestjs/common";
   
   @Injectable()
   export class PetService implements PetApi {
     addPet(pet: Pet, request: Request): Pet | Promise<Pet> | Observable<Pet> {
       throw new Error("Method not implemented.");
     }
   
     deletePet(petId: number, apiKey: string, request: Request): void | Promise<void> | Observable<void> {
       throw new Error("Method not implemented.");
     }
   
   ...

3. Import the generated ApiModule with ApiModule.forRoot and provide a instance of ApiImplementations with a reference to your implementation
   app.module.ts

   import { Module } from "@nestjs/common";
   import { ApiModule, ApiImplementations } from "api-module";
   import { PetService } from "./handlers/PetService";
   import { UserService } from "./handlers/UserService";
   import { StoreService } from "./handlers/StoreService";
   
   const apiImplementations: ApiImplementations = {
     petApi: PetService,
     userApi: UserService,
     storeApi: StoreService,
   }
   
   @Module({
     imports: [
       ApiModule.forRoot(apiImplementations),
     ],
     controllers: [],
     providers: [],
   })
   export class AppModule {}

You now can regenerate the API module as often as you want without overriding your implementation.

---

@TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo (2019/11) @amakhrov @davidgamero @mkusaka @joscha

[macjohnny]

thanks for adding this new generator!

[macjohnny]

@TiFu @bodograumann would it make sense to base this here on the TypeScriptClientCodegen?

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptClientCodegen.java

so we could re-use a lot of the model/imports handling?

[macjohnny]

is this expected?

[aryobenholzner]

It was created like this from the scaffolding from the Nest CLI. I'm not sure if it would work correctly for all projects if we change it to esNext. I don't think there would be any downsides if we keep it as commonjs . What do you think?

[macjohnny]

please use the nest version variable like in

openapi-generator/modules/openapi-generator/src/main/resources/typescript-nestjs/package.mustache

Line 32 in a5f638f

"@nestjs/common": "^{{nestVersion}}",

[aryobenholzner]

I cleaned up package.mustache and parameterized all versions

[macjohnny]

how is the implementer supposed to use this? can you clarify that in the PR description?

[aryobenholzner]

I updated the description as well as the committed README

[wing328]

thanks for the PR

suggestions:

• add a script similar to https://github.com/OpenAPITools/openapi-generator/blob/master/bin/configs/typescript-nestjs-v8-provided-in-root.yaml
• generate the samples (added to this PR)
• add the new folder to a new workflow to test typescript server samples in https://github.com/OpenAPITools/openapi-generator/tree/master/.github/workflows

[aryobenholzner]

Thanks a lot for the detailed feedback! 
I’m glad to see the comments coming in.

Apologies for any messiness at this stage. I wanted to get early feedback before spending time polishing things. There are probably a few things left from the initial NestJS scaffolding or generator code that doesn't serve any purpose here.

From what I gather, the overall approach seems acceptable. I’ll continue building on this and refining it based on your input. Let me know if anything fundamental needs to change!

[macjohnny]

@aryobenholzner is this ready for review?

[aryobenholzner]

@macjohnny I think it is. This is a working first version and I think it would be best to add more features later on.

[wing328]

@aryobenholzner can you please review the CI failure when you've time?

[aryobenholzner]

@wing328 it should be good now

[wing328]

ok but https://github.com/OpenAPITools/openapi-generator/actions/runs/16632831156/job/47097653123?pr=21494 still failed.

please take a look when you've time.

[aryobenholzner]

@wing328 the node version in the workflows were too old for this version of NestJS, should be fixed now. (unfortunately I can't seem to trigger these workflows myself)

[macjohnny]

does that run the same test as the github action? if so, it could be removed (can be done in a subsequent PR)