René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"response.union undefined","articleBody":"Version 2.7.2. go version 1.26.6. runtime 1.4.2.\n\nA natural migration from 2.6 -> 2.7.2 breaks for us.\n\nGoing from 2.6 to 2.7.2 introduced this: https://github.com/oapi-codegen/oapi-codegen/issues/2403 for our spec. The claimed fix is to upgrade the runtime to 1.4.2 `https://github.com/oapi-codegen/oapi-codegen/issues/2403#issuecomment-4756703428`.\n\nBumping the runtime to 1.4.2 then introduces `response.union undefined` for responses that utilize `oneOf`. I see numerous issues and questions lingering around this, so I'll not link them here. I would have expected a version bump for this lib just for this.\n\nChasing this down it looks like the first version it breaks on is 2.7.0. Similar reasons to other issues already opened.\n\n---\n\nReproducible spec:\n\n```\npackage: openapi\ngenerate:\n  std-http-server: true\n  strict-server: true\n  models: true\n  embedded-spec: true\noutput-options:\n  skip-prune: true\n```\n\n```\nopenapi: 3.0.3\ninfo:\n  title: repro\n  version: 1.0.0\npaths:\n  /things:\n    get:\n      operationId: listThings\n      responses:\n        '200':\n          description: OK\n          content:\n            application/json:\n              schema:\n                type: array\n                items:\n                  $ref: '#/components/schemas/Thing'\n        '400':\n          $ref: '#/components/responses/BadRequest'\n        '404':\n          $ref: '#/components/responses/NotFound'\ncomponents:\n  responses:\n    # This breaks: a *shared* (components/responses) response whose inline schema is a oneOf. Referenced from an operation via $ref.\n    BadRequest:\n      description: Invalid request\n      content:\n        application/json:\n          schema:\n            oneOf:\n              - $ref: '#/components/schemas/Error'\n              - $ref: '#/components/schemas/ValidationError'\n    # Doesn't break: same shape, but a plain $ref schema. Generates fine.\n    NotFound:\n      description: Resource not found\n      content:\n        application/json:\n          schema:\n            $ref: '#/components/schemas/Error'\n  schemas:\n    Thing:\n      type: object\n      required: [id]\n      properties:\n        id:\n          type: string\n    Error:\n      type: object\n      required: [error, message]\n      properties:\n        error:\n          type: string\n        message:\n          type: string\n    ValidationError:\n      type: object\n      required: [error, message]\n      properties:\n        error:\n          type: string\n        message:\n          type: string\n        fields:\n          type: array\n          items:\n            type: string\n\n```","author":{"url":"https://github.com/hammypants","@type":"Person","name":"hammypants"},"datePublished":"2026-08-21T19:02:25Z","url":"https://github.com/oapi-codegen/oapi-codegen/issues/2539"}