feat: add support for `oneOf` in sttp4 client by plaflamme · Pull Request #22916 · OpenAPITools/openapi-generator

plaflamme · 2026-02-07T03:32:57Z

Address #19891 for sttp4 clients.

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Summary by cubic

Adds oneOf support to the Scala sttp4 client, aligns JSON/request/response handling with sttp4, and updates samples, docs, and dependencies. Also fixes oneOf parents with own properties by propagating parent fields to children and resolving aliased children; adds tests. Fixes #19891.

New Features
- oneOf: sealed-trait parents; inline case classes when used by a single parent; discriminator + mapping; discriminator fields removed in children; circe/json4s codecs; tests incl. empty members and parent-prop cases; constructor-name mapping made total; parent-owned props rendered as abstract members on the sealed trait and propagated to each child; aliased children resolved via original $refs.
- API alignment: body(asJson(...)); Either[ResponseException[String], T]; pass Option[String] directly to .header; container query/form values encode via mkString(","); url-form-encoded bodies include only provided fields; default Seq params = Seq.empty; AnyType/object map to circe Json/JsonObject or json4s JValue/JObject based on jsonLibrary.
- Enums/samples/deps: enums replaced with sealed-trait ADTs and per-type codecs; json4s JsonSupport now uses the sealed-trait Serializer objects; new scala-sttp4-circe sample + CI; sttp client 4.0.15; Scala 2.13.18; add circe-generic and circe-generic-extras; semiauto derivation; docs updated (circeVersion/circeExtrasVersion).
Migration
- Enums are now sealed traits; update matches/usages and imports.
- oneOf parents are sealed traits; some members are generated inline; parent properties now appear on the parent trait and each child; adjust usages/imports if referenced directly.
- Response type is Either[ResponseException[String], T] (was ResponseException[String, Exception]).
- Query/form containers now use mkString(","); url-form-encoded bodies omit unset fields; verify server expectations.

^{Written for commit ac1b84e. Summary will update on new commits.}

cubic-dev-ai

4 issues found across 8 files

Prompt for AI agents (all issues)


Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="modules/openapi-generator/src/main/resources/scala-sttp4/api.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/scala-sttp4/api.mustache:38">
P2: Request bodies are now always JSON‑serialized with `asJson(...)`, which breaks operations that consume non‑JSON media types by sending JSON instead of the raw body.</violation>
</file>

<file name="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache:52">
P2: json4s oneOf deserialization aborts on first mismatch because `Extraction.extract` throws, so later oneOf types are never tried.</violation>

<violation number="2" location="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache:74">
P2: Discriminator handling hardcodes the Scala class name as the wire value, ignoring OpenAPI discriminator mappings, so specs with mapped discriminator values will fail to deserialize/serialize correctly.</violation>

<violation number="3" location="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache:172">
P2: Inline oneOf member case classes are generated inside the parent model file, but the parent model’s import list isn’t augmented with the child models’ imports. If a oneOf member uses a type not referenced by the parent, the inline case class will compile without the necessary import.</violation>
</file>

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modules/openapi-generator/src/main/resources/scala-sttp4/api.mustache

cubic-dev-ai · 2026-02-07T03:43:55Z

modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache

+{{/vendorExtensions.x-isEnum}}
+{{#vendorExtensions.x-isRegularModel}}
+{{^isEnum}}
+case class {{classname}}(


P2: Inline oneOf member case classes are generated inside the parent model file, but the parent model’s import list isn’t augmented with the child models’ imports. If a oneOf member uses a type not referenced by the parent, the inline case class will compile without the necessary import.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache, line 172: <comment>Inline oneOf member case classes are generated inside the parent model file, but the parent model’s import list isn’t augmented with the child models’ imports. If a oneOf member uses a type not referenced by the parent, the inline case class will compile without the necessary import.</comment> <file context> @@ -15,46 +20,218 @@ import {{import}} +{{/vendorExtensions.x-isEnum}} +{{#vendorExtensions.x-isRegularModel}} +{{^isEnum}} +case class {{classname}}( + {{#vars}} + {{#description}} </file context>

modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache

wing328 · 2026-02-07T06:30:50Z

thanks for the PR

cc @clasnake (2017/07), @shijinkui (2018/01), @ramzimaalej (2018/03), @chameleon82 (2020/03), @Bouillie (2020/04) @Fish86 (2023/06)

wing328 · 2026-02-07T12:40:23Z

https://github.com/OpenAPITools/openapi-generator/actions/runs/21774387501/job/62832048821?pr=22916

please follow step 3 to update the samples

cubic-dev-ai

1 issue found across 3 files (changes from recent commits).

Prompt for AI agents (all issues)


Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache:107">
P2: `transformConstructorNames` is defined as a partial match over only `x-oneOfMembers`. Because `x-oneOfMembers` excludes shared oneOf subtypes, the function is not total and will throw `MatchError` when encoding/decoding those subtypes. Add a default case (identity) so unmapped constructor names don’t crash serialization.</violation>
</file>

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modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache

plaflamme · 2026-02-09T18:56:07Z

@wing328 I've updated the samples in e594023

cubic-dev-ai

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (all issues)


Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache:110">
P2: Wildcard `case other` is emitted inside the oneOfMembers loop, so the first wildcard matches everything and makes subsequent member cases unreachable; only the first oneOf member can be encoded/decoded.</violation>
</file>

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modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache

On large APIs this can dramatically speed up compilation.

wing328 · 2026-02-11T09:20:35Z

https://github.com/OpenAPITools/openapi-generator/actions/runs/21850815146/job/63223036192?pr=22916

please replace tabs with 4-space in the java file.

plaflamme · 2026-02-11T23:54:38Z

@wing328 should be all good now

bin/configs/scala-sttp4-circe.yaml

samples/client/petstore/scala-sttp4/build.sbt

wing328 · 2026-02-12T16:17:18Z

please review the build failure when you've time.

let us know if you need any help

plaflamme · 2026-02-18T18:14:10Z

@wing328 I think this is good to go now?

# Conflicts: # modules/openapi-generator/src/test/java/org/openapitools/codegen/scala/Sttp4CodegenTest.java

…f Enumeration-based EnumNameSerializer The json4s variant of JsonSupport.scala used EnumNameSerializer which expects Scala Enumeration types, but sttp4 model templates generate sealed traits with case objects for enums. This caused compilation errors since the types are incompatible. Replace EnumNameSerializer with direct references to the implicit Serializer objects already defined in each enum's companion object.

plaflamme · 2026-03-06T20:12:50Z

@wing328 updated this on top of the latest master branch, anything else needed to get this in?

…ropagate parent props When a schema has both its own properties and a oneOf composition, the sttp4 generator previously had three issues: 1. Empty oneOf children (no type, no properties) were silently dropped because DefaultCodegen's unaliasSchema treated them as type aliases, replacing the model name with the language type (e.g. io.circe.Json). 2. Parent-owned properties (e.g. cancellation_datetime) were lost entirely - they didn't appear on the sealed trait or any child. 3. Sibling properties from other oneOf children could contaminate each child's vars list via DefaultCodegen's property merging. This fix: - Resolves aliased oneOf children by looking at the original OpenAPI schema's $refs to restore correct model names - Identifies parent-owned properties and propagates them to each child model's allVars so they appear in generated case classes - Renders parent properties as abstract def members on the sealed trait for compile-time enforcement - Adds a test covering the CancellationInfo pattern (parent with properties + oneOf with empty and non-empty children)

wing328 · 2026-03-17T16:15:29Z

will try to run some tests tomorrow and merge if no questions/feedback from anyone.

cubic-dev-ai bot reviewed Feb 7, 2026

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feat: add support for oneOf in sttp4 client

a0443cc

plaflamme force-pushed the sttp4-client-oneof branch from 1ec344d to c56b433 Compare February 7, 2026 04:43

fix: pass Option[String] directly to .header

4437a9e

plaflamme force-pushed the sttp4-client-oneof branch from c56b433 to 4437a9e Compare February 7, 2026 15:23

wing328 added Client: Scala Enhancement: Feature Feature: OAS 3.0 spec support labels Feb 9, 2026

wing328 added this to the 7.20.0 milestone Feb 9, 2026

fix: use oneOf mapping to map discriminator values to types

9b9f05e

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plaflamme added 2 commits February 9, 2026 13:25

fix: remove unecessary whitespaces

bd2a4bd

fix: generate samples, make a new one for sttp4-circe

e594023

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modules/openapi-generator/src/main/resources/scala-sttp4/model.mustache Outdated Show resolved Hide resolved

fix: make partial function total

7aba995

plaflamme force-pushed the sttp4-client-oneof branch from d05761d to 7aba995 Compare February 9, 2026 18:59

plaflamme added 2 commits February 9, 2026 22:33

fix: only use semiauto derivation

921be4b

On large APIs this can dramatically speed up compilation.

fix: missing comma

74a8c3e

plaflamme added 4 commits February 11, 2026 17:31

fix: re-run generate-samples script

4da2654

docs: update documentation

1e8c387

fix: spaces, not tabs

1e3be60

Merge remote-tracking branch 'upstream/master' into sttp4-client-oneof

ac70f60

wing328 reviewed Feb 12, 2026

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bin/configs/scala-sttp4-circe.yaml Show resolved Hide resolved

wing328 reviewed Feb 12, 2026

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samples/client/petstore/scala-sttp4/build.sbt Outdated Show resolved Hide resolved

ci: add new samples directory

545de95

fix: bump scala version

14227c6

fix: url-form-encoded cases

8de5683

wing328 mentioned this pull request Feb 13, 2026

feat: Add oneOf for scala-http4s client #22969

Open

6 tasks

wing328 modified the milestones: 7.20.0, 7.21.0 Feb 16, 2026

plaflamme added 3 commits March 6, 2026 14:32

Merge remote-tracking branch 'upstream/master' into sttp4-client-oneof

ce5ea99

# Conflicts: # modules/openapi-generator/src/test/java/org/openapitools/codegen/scala/Sttp4CodegenTest.java

chore: regenerate sttp4 samples after upstream merge

cabdbe6

plaflamme added 2 commits March 16, 2026 13:25

Merge remote-tracking branch 'upstream/master' into sttp4-client-oneof

ac1b84e

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