[kotlin][jvm-ktor] Fix query parameters typed as type:object (Map and model)

[AnarchyGhost]

Fixes #23762

Summary

Reworks query parameter handling in the jvm-ktor template to correctly serialize type: object schemas, plus a small KotlinClientCodegen change so the template can build correct deepObject URLs for models.

Three branches in kotlin-client/libraries/jvm-ktor/api.mustache:

• isModel
  • deepObject → per-field, key = paramBaseName[fieldBaseName]
  • form+explode=true → per-field, key = fieldBaseName
  • form+explode=false → single entry, CSV of field,value pairs (non-null fields only) under baseName
• isMap
  • deepObject → forEach with baseName[$key]
  • form+explode=true → forEach with bare $key
  • form+explode=false → joinToString(",") of map entries under baseName
• default (scalar / array) — unchanged

Behavior after the fix

schema	style / explode	URL
Map (additionalProperties:)	form / true	?k1=v1&k2=v2
Map	form / false	?param=k1,v1,k2,v2
Map	deepObject	?param[k1]=v1&param[k2]=v2
Model (properties:)	form / true	?field1=…&field2=…
Model	form / false	?param=field1,value1,field2,value2
Model	deepObject	?paramBaseName[field1]=…&paramBaseName[field2]=…

Implementation notes

KotlinClientCodegen now exposes the outer parameter's OAS baseName on each generated field via the x-kotlin-param-base-name vendor extension. The jvm-ktor template uses it for the deepObject URL prefix on models, since Mustache provides no access to the outer scope from inside {{#vars}}.

Note on parameter naming (snake_case vs camelCase)

For models with style: deepObject, the URL prefix is the OAS baseName, not the Kotlin identifier. Example: a parameter declared as

- name: model_deep
  in: query
  style: deepObject
  schema:
    type: object
    properties:
      a:
        type: string

generates a Kotlin parameter named modelDeep (camelCase), but the URL key remains ?model_deep[a]=… per OAS. This is the role of the new x-kotlin-param-base-name vendor extension: it propagates the parameter's baseName into the vars scope, which Mustache otherwise cannot reach.

For comparison, the existing jvm-okhttp template currently emits ?modelDeep[a]=… (kotlin paramName) in the same scenario. This PR does not touch jvm-okhttp — scope is intentionally limited to jvm-ktor.

Test plan

• New unit test KotlinClientCodegenApiTest#testJvmKtorQueryParamWithTypeObject covering the 6 affected (schema × style/explode) combinations plus a regression assertion that the old broken mapDeep?.apply { shape is gone.
• All 71 KotlinClient*Test cases pass.
• ./bin/generate-samples.sh ./bin/configs/kotlin-jvm-ktor-{gson,jackson,kotlinx_serialization}.yaml — no existing sample changed, the fix only activates new branches for previously broken cases.
• Additional runtime sanity check on a private playground: generated client routed through Ktor MockEngine produces the URLs in the table above for all 6 cases.

[cubic-dev-ai]

1 issue found across 4 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/api.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/api.mustache:137">
P1: Model query params ignore `explode=false` and always serialize each property as its own query key.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[AnarchyGhost]

@cubic-dev-ai Good catch — the isModel branch missed form + explode=false. Fixed in deeace10b55:

• Added a third sub-branch under {{#isModel}} for {{^isExplode}} (non-deepObject), generating a single query entry with the OAS-defined field,value CSV under baseName. Null fields are filtered via listOfNotNull, and the parameter is omitted entirely if all fields are null.
• Extended jvm-ktor-type-object-query.yaml with a model_form_noexplode parameter and added a corresponding assertion in KotlinClientCodegenApiTest#testJvmKtorQueryParamWithTypeObject.
• Verified the resulting URL via a Ktor MockEngine smoke test on a local playground: ProbeModel(a="hi", b=7) serializes to ?model_form_noexplode=a,hi,b,7 (URL-encoded %2C as expected).

All 71 KotlinClient*Test cases still pass; no existing samples changed.

[wing328]

Ran some tests locally and the result is good.

Thanks for contributing the fix.