Show oneOf/anyOf variants inside an allOf in API reference

[akira28]

An allOf that combines a base schema with a oneOf or anyOf now renders its variants in the API reference. Each object variant shows the shared base properties plus its own.

Affects: API reference

Prompt summary: Improve how the API Explorer renders anyOf, oneOf and allOf, starting with the cases that lose information today. This PR covers the first one: unions nested in an allOf.

Why

GetSchemaProperties merges only the properties of allOf members, so a oneOf or anyOf member contributes nothing. A reader sees the base properties and never learns that the value is one of several shapes.

What

Unions inside allOf

SchemaAnalyzer now recognises an allOf with a union member and classifies the schema as that union. The base members must contribute properties. An allOf that only wraps a union $ref keeps its previous rendering.

Variants carry the base properties

Each object variant expands to the base properties followed by its own, through the existing variant list. Array and primitive variants are left unchanged. Shared properties repeat in every variant, and the required lists of the base and the variant carry over, so required properties keep their badge. When a variant redefines a base property of the same name, the variant's definition wins.

Property rows

A union stops being listed as a plain nested object only when its properties come from an allOf. A union that declares properties itself keeps listing them, and ApiPropertyTreeBuilder hands the rest to the variant list.

Verify

dotnet test tests/Elastic.ApiExplorer.Tests/
# BuildPropertyList_AllOfWithOneOfMember_ExpandsVariantsSharingBaseProperties

Out of scope: $ref targets that are themselves allOf + oneOf, listing shared properties once instead of per variant, and the Markdown export output. Later PRs in this stack can cover them.

Stack: 1 of 1 so far, the bottom of the stack on main. Further fixes will be added on top.

🤖 Generated with Claude Code

[github-actions]

Docs preview (local build)

Handbook preview: https://docs-v3-preview.elastic.dev/elastic/docs-builder/pull/4313/

[github-actions]

Requesting changes due to a correctness issue in required-field propagation for the new allOf + union variant expansion path (see inline comment).

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[github-actions]

Requesting changes for two correctness regressions in the new allOf + union rendering path: shared union-level properties can disappear, and duplicate property names can lose variant-specific constraints.

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[github-actions]

Requesting changes for a correctness regression in the new allOf + oneOf/anyOf expansion path: properties/required declared on the union-bearing allOf member are dropped from rendered variants.

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[github-actions]

[HIGH] allOf union-member shared properties are dropped from expanded variants

TrySplitAllOfUnion removes the union member from bases, and ClassifyAllOfUnion later builds each variant from MergeBasesInto(split.Bases, o.Schema). That loses properties/required declared directly on the union member itself.

Concrete failure shape:

pet:
  allOf:
    - $ref: '#/components/schemas/Base'
    - type: object
      properties:
        kind: { type: string }
      required: [kind]
      oneOf:
        - $ref: '#/components/schemas/Cat'
        - $ref: '#/components/schemas/Dog'

With the new split path, kind is not included in either expanded variant (Cat/Dog), and its required badge is lost. Before this change, GetSchemaProperties(allOf) included that member’s direct properties.

Please include the union member’s own non-union constraints (its direct/allOf-derived properties and required set) when synthesizing each variant.

[akira28]

Superseded by #4327, which joins all seven PRs of this stack into one. The commits and the resolved review threads carry over.