René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"schema-merging-behavior v1: an allOf of a non-object $ref serializes under the member's type name","articleBody":"Found while reviewing #2514. It's pre-existing on `main`, and independent of that PR.\n\n## Problem\n\nUnder `schema-merging-behavior: v1` (or `old-merge-schemas: true`), an `allOf` member that is a `$ref` gets embedded in a struct, whatever its type:\n\n```go\ntype WrapName struct {\n\tName `yaml:\",inline\"`   // Name = string\n}\n```\n\n`encoding/json` only flattens embedded *structs*. It encodes an embedded field of any other type as a regular field named after the type. So when the referenced schema isn't an object (untyped `{}`, a primitive, an array, or a map from `additionalProperties`), the value goes on the wire wrapped in an object keyed by the Go type name:\n\n| member | v1 marshals as | expected | v1 unmarshals the expected value |\n|---|---|---|---|\n| `Untyped: {}` | `{\"Untyped\":\"x\"}` | `\"x\"` | error: cannot unmarshal string |\n| `Name: {type: string}` | `{\"Name\":\"x\"}` | `\"x\"` | error: cannot unmarshal string |\n| `Names: {type: array, items: {type: string}}` | `{\"Names\":[\"a\",\"b\"]}` | `[\"a\",\"b\"]` | error: cannot unmarshal array |\n| `Labels: {type: object, additionalProperties: {type: string}}` | `{\"Labels\":{\"k\":\"v\"}}` | `{\"k\":\"v\"}` | no error, but `Labels` is left empty |\n| `Obj: {type: object, properties: …}` | `{\"v\":\"x\"}` | `{\"v\":\"x\"}` | works |\n\nThis affects models, clients and servers alike, including strict-server responses. v2 and v3 are fine: they lower a single-member `allOf` to an alias (`type WrapName = Name`).\n\n## Reproduction\n\n```yaml\nopenapi: \"3.0.3\"\ninfo: {title: t, version: \"1\"}\npaths: {}\ncomponents:\n  schemas:\n    Name: {type: string}\n    WrapName:\n      allOf:\n        - $ref: '#/components/schemas/Name'\n```\n\nConfig: `generate: {models: true}`, `output-options: {skip-prune: true}`, `compatibility: {schema-merging-behavior: v1}`.\n\n```go\nb, _ := json.Marshal(WrapName{Name: \"x\"})\nfmt.Println(string(b)) // {\"Name\":\"x\"}, expected \"x\"\n\nvar w WrapName\nerr := json.Unmarshal([]byte(`\"x\"`), &w) // json: cannot unmarshal string into Go value of type WrapName\n```\n\nThe same happens for an `allOf` of an untyped `$ref` followed by sibling keywords (`allOf: [{$ref: Untyped}, {description: …}]`), and for a component that is itself such an `allOf`.\n\n## Notes\n\n- One fix keeps v1's Go shape, so `WrapName{Name: \"x\"}` still compiles: when every other member contributes no fields, generate `MarshalJSON`/`UnmarshalJSON` on the struct that delegate to the embedded non-object member. Switching those cases to an alias, as v2 does, would also fix the wire but would change the Go type.\n- The wire encoding has never matched the spec, so there's nothing to preserve there.\n- `internal/test/servers/strict/responsebody_v1` (added in the #2514 follow-up) records the current `{\"Untyped\": …}` encoding. Update it with the fix.\n","author":{"url":"https://github.com/mromaszewicz","@type":"Person","name":"mromaszewicz"},"datePublished":"2026-09-27T23:11:57Z","url":"https://github.com/oapi-codegen/oapi-codegen/issues/2590"}