fix(kotlin-spring): use correct Jackson 3 property path for WRITE_DATES_AS_TIMESTAMPS

[takkiraz]

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Fixes #23383

Summary

When using Spring Boot 4 with Jackson 3, the generated application.yaml contains an invalid property path that causes the application to fail at startup:

Failed to bind properties under 'spring.jackson.serialization' to java.util.Map<tools.jackson.databind.SerializationFeature, java.lang.Boolean>:

Reason: No enum constant tools.jackson.databind.SerializationFeature.WRITE_DATES_AS_TIMESTAMPS

Root cause: In Jackson 3.x, WRITE_DATES_AS_TIMESTAMPS was moved from SerializationFeature to DateTimeFeature. The Spring Boot property path changed from:

• Jackson 2.x: spring.jackson.serialization.WRITE_DATES_AS_TIMESTAMPS
• Jackson 3.x: spring.jackson.datatype.datetime.WRITE_DATES_AS_TIMESTAMPS

Changes

• Updated kotlin-spring template to use conditional logic based on useSpringBoot4 flag
• Updated kotlin-springboot-4 sample with correct property path
• Added tests to verify correct property path for both Spring Boot 3 and Spring Boot 4

This aligns the kotlin-spring generator with the existing behavior in the JavaSpring generator.

How to validate

1. Generate a kotlin-spring server with Spring Boot 4:

   openapi-generator-cli generate -g kotlin-spring -i petstore.yaml -o out \
     --additional-properties=useSpringBoot4=true,useJackson3=true

2. Check out/src/main/resources/application.yaml contains:

   jackson:
     datatype:
       datetime:
         WRITE_DATES_AS_TIMESTAMPS: false

3. Run the server:

   cd out && ./gradlew bootRun

4. Server should start successfully

Technical Committee

@cachescrubber @DKoyama @jmini @shibasis0801 @welshm @Zomzog

---

Summary by cubic

Fixes a startup failure in kotlin-spring Spring Boot 4 projects by generating the correct Jackson 3 path for WRITE_DATES_AS_TIMESTAMPS. Aligns behavior with JavaSpring. Fixes #23383.

• Bug Fixes
  • Use spring.jackson.datatype.datetime.WRITE_DATES_AS_TIMESTAMPS when useSpringBoot4=true (Jackson 3).
  • Keep spring.jackson.serialization.WRITE_DATES_AS_TIMESTAMPS for Spring Boot 3 (Jackson 2).
  • Updated application.mustache, sample application.yaml, and added tests to verify the correct path and ensure the other path is absent.

^{Written for commit 68a77f1. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files