[swift] New 'swift-combine' client generator for swift

[dydus0x14]

iOS team of my current project used existing Swift generator for a year, but I decided to implement and open source an alternative solution to support critical features for our project:

• No 3rd-party dependencies used in generated code
• No static methods and global scopes for APIs: it allows to reuse and customize APIs in one app
• Multiply openapi files support: generator creates one OpenAPITransport library for all APIs as a dependency

Other nuances:

• It is Apple Combine framework based solution
• Applied optimizations for generated code:
  • less runtime types checks as possible
  • some utils methods defined in generated code only if used.
• It is first basic version and does not support all features of OpenAPI schema. Still a lot of things to do.

Examples: https://github.com/dydus0x14/openapi-generator-swift-combine

Some metrics: currently my iOS project contains 19 open api files (20k of YAML and JSON lines) and 25k lines of code generated by swift-combine generator.

Swift technical committee: @jgavris @ehyche @Edubits @jaz-ah @4brunu

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• In case you are adding a new generator, run the following additional script :

  ./bin/utils/ensure-up-to-date
  

  Commit all changed files.
• File the PR against the correct branch: master (6.3.0) (minor release - breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[wing328]

thanks for the PR. can this be added to swift5 via the library option instead? currently the following is supported:

urlsession
  [DEFAULT] HTTP client: URLSession
alamofire
  HTTP client: Alamofire
vapor
  HTTP client: Vapor

[4brunu]

Hi, thanks for taking the time to improve openapi-generator.
Like @wing328 I would prefer to take those improvements into the existing generator, rather than creating a new one.
For example, No static methods and global scopes for APIs: it allows to reuse and customize APIs in one app is something that other people have asked in the past.

[dydus0x14]

Hi @4brunu @wing328 and thanks for your feedback!

I thought about updating current generator instead of creating new one, but it seemed too difficult for me to support all described above bullet points for existing swift generator (due to architecture change and bunch of existing library options to support) and do not break backward compatibility.

How would you see a point about 'No static methods' might be integrated to the current generator? As I see there are several options:

• Without the library options, just change current APIs signatures in templates and break backward compatibility.
• With some library option which replace static with no static methods

[4brunu]

Hi, I think we need to have an option to let people decide which one they want to use.

[dydus0x14]

Ok, so if we do not interested in new generator I may close this PR and open new one for 'No static methods' feature for existing generator once it's ready.

[wing328]

I'm ok to accept it to give people another option and to try it out so as to collect more feedback.

@4brunu and I suggested adding it to the existing swift5 generator since it's easier to maintain based on our experience. If it's too hard to add swift-combine into the existing swift5 generator via the library option, we won't go that path.

[wing328]

can you please update bitrise.yml to run tests for swift-combine petstore samples?

[dydus0x14]

@wing328 done

[wing328]

the birise CI tests failed: https://app.bitrise.io/build/10f86487-ec07-44be-9058-5a5f7fe42535

can you please take a look when you've time?

[dydus0x14]

the birise CI tests failed: https://app.bitrise.io/build/10f86487-ec07-44be-9058-5a5f7fe42535

can you please take a look when you've time?

Sure, looks like I fixed it, but have no idea how to rerun bitrise pipelines.

[wing328]

trigger a build in https://app.bitrise.io/build/5f640a77-25ad-42f1-bf05-e5d206ea804c. let's see how that goes

[wing328]

bitrise tests passed via https://app.bitrise.io/build/5f640a77-25ad-42f1-bf05-e5d206ea804c

[wing328]

successfully triggered a build failure too so all good

@dydus0x14 can you please PM me via Slack when you've time? Thank you.

[wing328]

circieci failure not related to this change.

[wing328]

I'll remove this in another PR as it'a a new file

https://opensource.stackexchange.com/questions/7300/copyright-notice-in-the-file-header-apache-v2-license

[tivadarmolitorisz]

Hi @dydus0x14, why did you use Combine? It's basically dead, async/await should be used instead. Your basic idea is great, to have a solution without 3rd party dependencies, etc, so the question is, are you/your team planning to replace this approach?

[dydus0x14]

Hi @tivadarmolitorisz, thanks! Actually I implemented and used this generator for my project much earlier than WWDC 2023, so I had no idea about such move from Apple side😁 But I still decided to open source it because someone may still use Combine framework for like service layer in app. Now I do not have any plans to get away from Combine in my project, but it might be a great idea to create the similar Swift generator with async/await public signatures. So if you or your team is interested to use it, I can do it.

[tivadarmolitorisz]

@dydus0x14 we're interested in it, probably you should look for a new name for your generator (not swift-combine) and support the async-await operations as well, for example, swift-nextgen.