[TypeScript] Implement oneOf type resolution without discriminator

[ksvirkou-hubspot]

Summary

• Implements oneOf type resolution for TypeScript generator when discriminator is not present
• Adds OneOfClass with findMatchingType() method to determine correct type at runtime
• Enhances ObjectSerializer to use type deduction when discriminator is unavailable
• Includes comprehensive tests validating both discriminator and non-discriminator scenarios

Why

Previously, the TypeScript generator could only resolve oneOf types when a discriminator property was defined in the OpenAPI spec. This limitation meant that valid oneOf schemas without discriminators would fail at runtime.

This change enables automatic type resolution by checking which schema matches the provided data based on required fields, making the generated TypeScript clients more robust and easier to use for specs that don't define discriminators.

Implementation Details

• Created OneOfClass base class with instanceOf() method to validate objects against schema requirements
• Generated oneOf models now extend OneOfClass and include findMatchingType() to iterate through possible types
• ObjectSerializer checks for findMatchingType() method when discriminator is undefined and uses it for type resolution
• Falls back to original behavior if neither discriminator nor findMatchingType() is available
• Throws descriptive error when type resolution is ambiguous (object matches multiple or no schemas)

Tests

Added integration tests at samples/openapi3/client/petstore/typescript/tests/one-of/:

• Test spec: modules/openapi-generator/src/test/resources/3_0/typescript/oneOf.yaml defines two endpoints with oneOf responses
• Without discriminator test: Validates that PetResponse (oneOf without discriminator) correctly deserializes to Cat based on required fields (name, petType)
• With discriminator test: Validates that PetDiscriminatorResponse (oneOf with discriminator) correctly deserializes to Dog using discriminator property
• Tests use Mocha + Chai with Nock for HTTP mocking
• Run with: npm test in the test directory

Related issue: #19868

PR checklist

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[ksvirkou-hubspot]

The PR contains breaking change to generated TypeScript code, attributeTypeMap structure changed: Added required: boolean field to all model attribute type maps
- Before: Array<{name: string, baseName: string, type: string, format: string}>
- After: Array<{name: string, baseName: string, type: string, format: string, required: boolean}>
I can create method in model getRequiredFields() or create PR agains 8.0.0
Please check the PR and provide code review

[macjohnny]

thanks for the changes!

[ksvirkou-hubspot]

Could you please check the PR again?
I've added significant changes.
Do I need to create a new PR against the 8.0 branch?
@macjohnny

[ksvirkou-hubspot]

Any updates?
@macjohnny

[macjohnny]

sorry for the delay, will try to find some time, its quite a complex PR

[ksvirkou-hubspot]

Hi @macjohnny , just checking in on this PR.
Let me know if you need anything from me.
Thanks a lot for your time!

[ksvirkou-hubspot]

Any updates?
@macjohnny

[macjohnny]

@ksvirkou-hubspot I still didnt find time to thoroughly review this, but if you tested this thoroughly, i am fine merging that, just waiting for your confirmation.

are the tests of the samples/openapi3/client/petstore/typescript/tests/one-of/pom.xml correctly executed as part of the CI? i guess they would need to be configured somewhere here no? https://github.com/OpenAPITools/openapi-generator/tree/master/.github/workflows

[macjohnny]

could we somehow do without an extended CodegenModel class? everytime the base class is updated (e.g. new properties are added), this would need to be updated here as well

[ksvirkou-hubspot]

Alternatively, we could consider moving our additional properties to the base class itself.

I've extended the CodegenModel class because I need to add new properties specific to oneOf constructions. As far as I understand, extending the base class is a common approach — for example, the typescript-fetch generator uses the same pattern with its own ExtendedCodegenModel class.

openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptFetchClientCodegen.java

Line 1533 in 03c13fb

public class ExtendedCodegenModel extends CodegenModel {

[cubic-dev-ai]

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

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=".github/workflows/samples-typescript-client.yaml">

<violation number="1" location=".github/workflows/samples-typescript-client.yaml:124">
P2: CI wiring for the new oneOf sample excludes the `tests/one-of` suite, so test-only changes won't trigger or run in this workflow.</violation>
</file>

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

[cubic-dev-ai]

P2: CI wiring for the new oneOf sample excludes the tests/one-of suite, so test-only changes won't trigger or run in this workflow.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At .github/workflows/samples-typescript-client.yaml, line 124:

<comment>CI wiring for the new oneOf sample excludes the `tests/one-of` suite, so test-only changes won't trigger or run in this workflow.</comment>

<file context>
@@ -119,6 +121,7 @@ jobs:
           - samples/openapi3/client/petstore/typescript/builds/browser/
           #- samples/openapi3/client/petstore/typescript/tests/browser/
           #- samples/openapi3/client/petstore/typescript/builds/nullable-enum/
+          - samples/openapi3/client/petstore/typescript/builds/one-of/
           - samples/client/petstore/typescript-fetch/builds/default/
           - samples/client/petstore/typescript-fetch/builds/es6-target/
</file context>