[kotlin][client] Respect explicit useJackson3=false with useSpringBoot4 on jvm-spring-restclient

[seonwooj0810]

Fixes #24842

Since #24709, useSpringBoot4=true on jvm-spring-restclient switches to Jackson 3 even when the user explicitly sets useJackson3=false. The check used !isUseJackson3(), which cannot tell "not set" from "explicitly false". It can't because AbstractKotlinCodegen.processOpts() always writes useJackson3 back into additionalProperties. Projects that compiled with 7.24.0 against their own Jackson 2 build (see the issue) now get a tools.jackson Serializer.kt and JacksonJsonHttpMessageConverter.

The fix records whether useJackson3 was configured before super.processOpts(). Jackson 3 is only auto-enabled when the option was not set. With useSpringBoot4=true alone, the output is unchanged and still Jackson 3 by default. An explicit useJackson3=false now generates the Jackson 2 serializer, the MappingJackson2HttpMessageConverter constructor and the Jackson 2 Gradle dependencies.

Verification done:

• Added KotlinClientCodegenModelTest.shouldRespectExplicitJackson3FalseWithSpringBoot4. It fails without the change because PetApi.kt has no MappingJackson2HttpMessageConverter, and passes with it.
• KotlinClientCodegenModelTest (69) and KotlinClientCodegenApiTest (31) pass, including the existing shouldAutoEnableJackson3WithSpringBoot4.
• Regenerated kotlin-jvm-spring-4-restclient-jackson3, kotlin-jvm-spring-3-restclient and kotlin-jackson3: no sample diff. export_docs_generators.sh: no doc diff.
• Generated a client with useSpringBoot4=true,useJackson3=false (with and without useSpringBoot3=true). ./gradlew compileKotlin succeeds against Spring Boot 4.1.0 + Jackson 2.22.1 (Gradle 8.14.5, JDK 21).

PR checklist

• Read the contribution guidelines.
• Ran the build/tests for modules/openapi-generator, regenerated the affected Kotlin samples (no changes) and exported docs (no changes).
• @mention technical committee — deferring to maintainers.

---

Summary by cubic

Fixes #24842 by honoring an explicit useJackson3=false on jvm-spring-restclient instead of overriding it when useSpringBoot4=true is set. Since #24709, processOpts() always wrote useJackson3 back, so the generator couldn't tell "not set" from "explicitly false" and auto-enabled Jackson 3. The check now records whether the option was configured before processOpts() runs. With useSpringBoot4=true alone, the output is unchanged and still defaults to Jackson 3; an explicit useJackson3=false now generates the Jackson 2 serializer, the MappingJackson2HttpMessageConverter constructor, and the Jackson 2 Gradle dependencies.

• Adds a regression test covering explicit useJackson3=false with useSpringBoot4=true.

^{Written for commit daf9dc0. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java:444">
P2: `setUseJackson3(false)` leaves no map entry, so this check treats the caller's explicit choice as omitted and enables Jackson 3 for Boot 4. Track setter-configured values too.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: setUseJackson3(false) leaves no map entry, so this check treats the caller's explicit choice as omitted and enables Jackson 3 for Boot 4. Track setter-configured values too.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java, line 444:

<comment>`setUseJackson3(false)` leaves no map entry, so this check treats the caller's explicit choice as omitted and enables Jackson 3 for Boot 4. Track setter-configured values too.</comment>

<file context>
@@ -440,6 +440,9 @@ public void processOpts() {
         }
 
+        // super.processOpts() always writes useJackson3 back, so remember whether the user set it
+        boolean useJackson3Configured = additionalProperties.containsKey(USE_JACKSON_3);
+
         super.processOpts();
</file context>

[wing328]

thanks for the PR

cc @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03) @stefankoppier (2022/06) @e5l (2024/10)