feat: Add oneOf for scala-http4s client

[bartosz822]

Implement oneOf schema support for scala-http4s client generator using sealed traits with inlined members. Falls back to regular traits for edge cases (nested oneOf, mixed members).

• Add postProcessAllModels to detect and mark oneOf models
• Update model.mustache for sealed/regular trait generation
• Support all discriminator modes (none, implicit, mapping)
• Fix Scala 3 syntax (wildcard imports with *)
• Handle shared members and import management
• Add test and regenerate samples

Common oneOf schemas generate sealed traits for exhaustive pattern matching. Edge cases use regular traits and emit warnings. All generated code compiles.

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---

Summary by cubic

Add oneOf support to the scala-http4s client generator. Generates sealed traits with inlined members, handles all discriminator modes, and falls back to regular traits for edge cases.

• New Features

  • Detect oneOf in postProcessAllModels and emit sealed traits; nested/mixed oneOf use regular traits with warnings.
  • Support discriminator modes: none, implicit, and mapping, with Circe encoders/decoders, Cats widen, and DecodingFailure on unknown values.
  • Inline member imports, skip separate files for inlined variants, prevent extending multiple sealed traits, and split X-implements into extends/with.
  • Update template and docs; expand tests to assert sealed trait generation, discriminator handling, Scala 3 syntax, and that inlined members don't generate files.

• Bug Fixes

  • Fix Scala 3 wildcard import syntax (*) in generated models.

^{Written for commit 00184fd. Summary will update on new commits.}

[cubic-dev-ai]

2 issues found across 13 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/java/org/openapitools/codegen/languages/ScalaHttp4sClientCodegen.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ScalaHttp4sClientCodegen.java:393">
P2: Nested oneOf models can be incorrectly inlined as case classes because the inlining condition doesn’t exclude child models that are oneOf containers, causing nested oneOf traits to be dropped from output and generating incorrect models.</violation>
</file>

<file name="modules/openapi-generator/src/main/resources/scala-http4s/model.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/scala-http4s/model.mustache:47">
P2: Discriminator handling without mapping uses generated class names rather than schema names, which can break decoding/encoding when schema names differ from class names.</violation>
</file>

---

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[cubic-dev-ai]

P2: Nested oneOf models can be incorrectly inlined as case classes because the inlining condition doesn’t exclude child models that are oneOf containers, causing nested oneOf traits to be dropped from output and generating incorrect models.

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/java/org/openapitools/codegen/languages/ScalaHttp4sClientCodegen.java, line 393:

<comment>Nested oneOf models can be incorrectly inlined as case classes because the inlining condition doesn’t exclude child models that are oneOf containers, causing nested oneOf traits to be dropped from output and generating incorrect models.</comment>

<file context>
@@ -354,6 +357,162 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
+                    Set<String> additionalImports = new HashSet<>();
+                    for (String childName : cModel.oneOf) {
+                        CodegenModel childModel = allModels.get(childName);
+                        if (childModel != null && oneOfMemberCount.getOrDefault(childName, 0) == 1) {
+                            // Mark for inlining (only used by this one parent)
+                            childModel.getVendorExtensions().put("x-isOneOfMember", true);
</file context>

Suggested change

	if (childModel != null && oneOfMemberCount.getOrDefault(childName, 0) == 1) {
	if (childModel != null
	+ && (childModel.oneOf == null || childModel.oneOf.isEmpty())
	+ && oneOfMemberCount.getOrDefault(childName, 0) == 1) {

[cubic-dev-ai]

P2: Discriminator handling without mapping uses generated class names rather than schema names, which can break decoding/encoding when schema names differ from class names.

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-http4s/model.mustache, line 47:

<comment>Discriminator handling without mapping uses generated class names rather than schema names, which can break decoding/encoding when schema names differ from class names.</comment>

<file context>
@@ -16,6 +17,173 @@ import {{import}}
+// with discriminator, no mapping
+  given encoder{{classname}}: Encoder[{{classname}}] = Encoder.instance {
+{{#oneOf}}
+    case obj: {{.}} => obj.asJson.mapObject(("{{discriminator.propertyName}}" -> "{{.}}".asJson) +: _)
+{{/oneOf}}
+  }
</file context>

[wing328]

@bartosz822 thanks for the PR

is the implementation same as the one in #22916 authored by @plaflamme ?