feat(kotlin-spring): add suspendFunctions option for coroutine support

[thejeff77]

Summary

• Adds a new suspendFunctions boolean config option (default: false) to the kotlin-spring generator
• When enabled, all generated API operations get the suspend keyword on controller interfaces, delegate interfaces, service interfaces, and standalone controllers
• Enables Spring MVC + Kotlin coroutines without requiring the full reactive stack (WebFlux/Flow), eliminating the need for runBlocking in delegate implementations

Changes

• KotlinSpringServerCodegen.java: Added constant, field, CLI switch, and processOpts() handling
• api.mustache, apiDelegate.mustache, apiInterface.mustache, service.mustache: Added suspend keyword when suspendFunctions=true, falling back to existing reactive logic when false
• KotlinSpringServerCodegenTest.java: 3 new tests (interface-only, delegate pattern, defaults-to-false)
• docs/generators/kotlin-spring.md: Documented new option

Usage

configOptions:
  delegatePattern: "true"
  suspendFunctions: "true"

Test plan

• suspendFunctionsInterfaceOnly — verifies suspend fun in interface-only mode
• suspendFunctionsWithDelegatePattern — verifies suspend fun in both API interface and delegate
• suspendFunctionsDefaultsToFalse — verifies no suspend when option not set
• Existing reactive tests pass (no regressions)

🤖 Generated with Claude Code

---

Summary by cubic

Adds a new suspendFunctions option to the kotlin-spring generator to emit suspend for all API operations, enabling Kotlin coroutines with Spring MVC without WebFlux. Default is false; no changes unless enabled, removing the need for runBlocking in delegates and services.

• New Features

  • New suspendFunctions switch (default: false) in KotlinSpringServerCodegen; exposed via CLI addSwitch, persisted via processOpts, configurable via additionalProperties/configOptions.
  • Templates (api.mustache, apiInterface.mustache, apiDelegate.mustache, service.mustache) add suspend when enabled; otherwise use existing reactive logic. Works with delegatePattern, serviceInterface, and interface-only. Docs updated (option added to table).

• Bug Fixes

  • Tests read files with StandardCharsets.UTF_8 to satisfy the forbiddenapis plugin.

^{Written for commit a8ab0af. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

No issues found across 7 files

[thejeff77]

Requesting Review

Tagging the Kotlin technical committee and recent active contributors to the kotlin-spring generator for visibility:

Kotlin TC: @karismann @Zomzog @4brunu @yutaka0m @stefankoppier @e5l @dennisameling

Recent active contributors to kotlin-spring: @metlicka @wing328 @neeme-praks-sympower @takkiraz

This PR adds a suspendFunctions config option (default: false) that generates suspend fun for all API operations without requiring the full reactive stack. It's useful for Spring MVC + Kotlin coroutines — the current workaround is wrapping delegate calls in runBlocking, which this eliminates.

The change is minimal (8 lines in the codegen class, 1 line per template × 4 templates) and backward-compatible.

[thejeff77]

Friendly bump! 👋 Would love to get some eyes on this when anyone has a chance.

Kotlin TC: @karismann @Zomzog @4brunu @yutaka0m @stefankoppier @e5l @dennisameling
Recent kotlin-spring contributors: @metlicka @wing328

Happy to address any feedback. Thanks!

[thejeff77]

Re: the failing ci/circleci: node0 check — this is unrelated to this PR. The failure is in the openapi-generator-gradle-plugin Maven wrapper build:

Plugin org.fortasoft:gradle-maven-plugin:1.0.8 or one of its dependencies could not be resolved

All actual openapi-generator modules (core library, executable, maven-plugin) built and tested successfully. The other 3 CircleCI nodes pass, and all GitHub Actions checks are green.

[wing328]

@thejeff77 thanks for the PR

can you please resolve the merge conflicts when you've time?

Then please PM me via Slack to have this reviewed and merged

https://join.slack.com/t/openapi-generator/shared_invite/zt-36ucx4ybl-jYrN6euoYn6zxXNZdldoZA

[wing328]

Ran some tests locally and the result is good.

Thanks for the contribution.