René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Nested nullable unions silently discard JSON payloads","articleBody":"An OpenAPI 3.1 nullable wrapper around an inline `oneOf` or `anyOf` generates a union struct without its JSON methods. Generation succeeds, but unmarshalling and then marshalling silently drops the union payload.\n\nReproduced on `main` at `833a968f84b4b0ec7c2f3fb5bb119e3c449f7a4f`, using Go 1.27.1 on darwin/arm64, with `compatibility.schema-merging-behavior` set to `v1`, `v2`, or `v3`.\n\n### Reproduction\n\nSave these three files in a new directory. The reproduction is provided under Apache-2.0.\n\n`spec.yaml`:\n\n```yaml\nopenapi: 3.1.0\ninfo:\n  title: Nested nullable union reproduction\n  version: 1.0.0\npaths: {}\ncomponents:\n  schemas:\n    Envelope:\n      type: object\n      required: [pet]\n      properties:\n        pet:\n          anyOf:\n            - oneOf:\n                - $ref: '#/components/schemas/Cat'\n                - $ref: '#/components/schemas/Dog'\n            - type: 'null'\n    Cat:\n      type: object\n      required: [meow]\n      properties:\n        meow: {type: string}\n    Dog:\n      type: object\n      required: [bark]\n      properties:\n        bark: {type: string}\n```\n\n`config.yaml`:\n\n```yaml\npackage: repro\noutput: types.gen.go\ngenerate:\n  models: true\noutput-options:\n  skip-prune: true\n```\n\n`repro_test.go`:\n\n```go\npackage repro\n\nimport (\n\t\"encoding/json\"\n\t\"testing\"\n)\n\nfunc TestNestedNullableUnionRoundTrip(t *testing.T) {\n\tconst input = `{\"pet\":{\"meow\":\"purr\"}}`\n\tvar value Envelope\n\tif err := json.Unmarshal([]byte(input), &value); err != nil {\n\t\tt.Fatal(err)\n\t}\n\toutput, err := json.Marshal(value)\n\tif err != nil {\n\t\tt.Fatal(err)\n\t}\n\tif string(output) != input {\n\t\tt.Fatalf(\"got %s, want %s\", output, input)\n\t}\n}\n```\n\nRun:\n\n```sh\ngo mod init example.com/nested-nullable-repro\ngo run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen@833a968f84b4b0ec7c2f3fb5bb119e3c449f7a4f --config=config.yaml spec.yaml\ngo get github.com/oapi-codegen/runtime@v1.7.0\ngo test .\n```\n\nActual result:\n\n```text\ngot {\"pet\":{}}, want {\"pet\":{\"meow\":\"purr\"}}\n```\n\nExpected: the complete payload survives the JSON round trip.\n\n### Cause\n\nThe nullable-union collapse path drops `UnionElements` and `Discriminator`, so the union's JSON methods and accessors are not generated.\n\nRelated to #2218. This reproduces after the OpenAPI 3.1 support added in #2336.\n","author":{"url":"https://github.com/g-logunov","@type":"Person","name":"g-logunov"},"datePublished":"2026-09-24T13:26:28Z","url":"https://github.com/oapi-codegen/oapi-codegen/issues/2565"}