[BUG][kotlin-spring] Fix defaultValue for RequestHeader is not generated (#20504)

[cgpoh]

This PR will fix 20504. Copied the current Java spring generator logic for the Kotlin Spring generator.

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 || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in Git BASH)
  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*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.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.

@jimschubert (2017/09) ❤️, @dr4ke616 (2018/08) @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03)

[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/14189376808/job/39750844839?pr=21003

please follow step 3 to update the samples

(in windows, you may need to run the command in WSL)

[cgpoh]

@wing328 , thanks! I've updated the samples.

[wing328]

i did a test with the spec provided in the issue but got errors:

$ ./gradlew build

> Task :compileKotlin FAILED
e: file:///C:/Users/wing3/AppData/Local/Temp/kotlin-spring/src/main/kotlin/org/openapitools/api/PetApiController.kt:68:317 Unresolved reference: de

FAILURE: Build failed with an exception.

does it work for your use cases locally with this fix?

[wing328]

and here is the change with this fix (compared with master)

--- a/src/main/kotlin/org/openapitools/api/PetApiController.kt
+++ b/src/main/kotlin/org/openapitools/api/PetApiController.kt
@@ -65,7 +65,7 @@ class PetApiController() {
         method = [RequestMethod.DELETE],
         value = ["/pet/{petId}"]
     )
-    fun deletePet(@Parameter(description = "Pet id to delete", required = true) @PathVariable("petId") petId: kotlin.Long,@Parameter(description = "", `in` = ParameterIn.HEADER, schema = Schema(allowableValues = ["de", "at"], defaultValue = "de")) @RequestHeader(value = "x-tenant", required = false) xTenant: kotlin.String,@Parameter(description = "", `in` = ParameterIn.HEADER) @RequestHeader(value = "api_key", required = false) apiKey: kotlin.String?): ResponseEntity<Unit> {
+    fun deletePet(@Parameter(description = "Pet id to delete", required = true) @PathVariable("petId") petId: kotlin.Long,@Parameter(description = "", `in` = ParameterIn.HEADER, schema = Schema(allowableValues = ["de", "at"], defaultValue = "de")) @RequestHeader(value = "x-tenant", required = false, defaultValue = de) xTenant: kotlin.String,@Parameter(description = "", `in` = ParameterIn.HEADER) @RequestHeader(value = "api_key", required = false) apiKey: kotlin.String?): ResponseEntity<Unit> {
         return ResponseEntity(HttpStatus.NOT_IMPLEMENTED)
     }

[cgpoh]

I just did a ./gradlew build in openapi-generator/samples/server/petstore/kotlin-spring-default and the build is successful. How to replicate the error?

[wing328]

please use https://gist.github.com/wing328/bb5ce7ec9a91527a67b4c0f1a3c95737 to reproduce the issue