Specify "type" for enums in OpenAPI

[Youssef1313]

Specify "type" for enums in OpenAPI

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Description

When encountering an enum in schema, we set the type to "string" instead of leaving it as null.

Fixes #61303

[Copilot]

Pull request overview

Updates OpenAPI schema generation so enums serialized as strings (e.g., via JsonStringEnumConverter) get an explicit "type": "string" instead of leaving type unset, aligning generated specs with expected OpenAPI schema shape.

Changes:

• Set type: "string" on enum schemas when an enum array is present but type is missing.
• Update the parameter schema test to assert JsonSchemaType.String for enum parameters using string enum conversion.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs	Adds enum-specific schema fix-up during STJ schema export transform.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs	Updates enum-with-converter test assertion to expect type to be string.