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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"x-go-type on a schema with allOf is silently ignored; first member's x-go-type leaks through instead","articleBody":"## Summary\n\nWhen a schema has both `allOf` and `x-go-type`, the `x-go-type` directive on the schema itself is silently ignored. Worse, if any `allOf` member has its own `x-go-type`, that override leaks through and becomes the alias target for the outer schema — producing a nonsensical alias that drops fields the user expects.\n\nThis was originally surfaced as an overlay issue in https://github.com/oapi-codegen/oapi-codegen/pull/2087, but the bug is **unrelated to overlays**. Overlays merely make it easy to add `x-go-type` to a third-party spec; the same misbehavior reproduces with a hand-edited spec containing no overlay at all.\n\n## Reproduction\n\nSpec:\n\n```yaml\ncomponents:\n  schemas:\n    Client:\n      x-go-type: OverlayClient\n      type: object\n      required: [name]\n      properties:\n        name: { type: string }\n    ClientWithId:\n      x-go-type: OverlayClientWithId\n      allOf:\n        - $ref: '#/components/schemas/Client'\n        - properties:\n            id: { type: integer }\n          required: [id]\n```\n\nUser-provided Go types `OverlayClient{Name}` and `OverlayClientWithId{Id, Name}`.\n\nExpected output:\n\n```go\ntype Client       = OverlayClient\ntype ClientWithId = OverlayClientWithId\n```\n\nActual output:\n\n```go\ntype Client       = OverlayClient\ntype ClientWithId = OverlayClient   // wrong\n```\n\nPR #2087 contains a runnable demonstration in `examples/anyof-allof-oneof/`.\n\n## Root cause\n\nThere are two compounding bugs.\n\n**(1) `pkg/codegen/schema.go:335-342`** — The `allOf` branch in `GenerateGoSchema` returns before the `x-go-type` check at line 344:\n\n```go\nif schema.AllOf \\!= nil {\n    mergedSchema, err := MergeSchemas(schema.AllOf, path)\n    ...\n    return mergedSchema, nil   // early return; x-go-type never consulted\n}\n\n// Check x-go-type, which will completely override the definition ...\nif extension, ok := schema.Extensions[extPropGoType]; ok { ... }\n```\n\nThe code comment explicitly states `x-go-type` \"will completely override the definition of this schema\" — this contract is violated when the outer schema uses `allOf`.\n\n**(2) `pkg/codegen/merge_schemas.go:113-116`** — `mergeOpenapiSchemas` unions extensions from both sides without filtering out Go-specific directives:\n\n```go\nresult.Extensions = make(map[string]any, len(s1.Extensions)+len(s2.Extensions))\nmaps.Copy(result.Extensions, s1.Extensions)\nmaps.Copy(result.Extensions, s2.Extensions)\n```\n\nSo `Client`'s `x-go-type: OverlayClient` is copied into the merged schema's extensions. `mergeSchemas` then recursively calls `GenerateGoSchema` on the merged schema (line 62), which this time has no `AllOf`, hits the `x-go-type` branch, and emits `type ClientWithId = OverlayClient`.\n\n## Version\n\nReproduced on `main` as of PR #2087 (commit f64f92b).","author":{"url":"https://github.com/mromaszewicz","@type":"Person","name":"mromaszewicz"},"datePublished":"2026-04-23T18:04:36Z","url":"https://github.com/oapi-codegen/oapi-codegen/issues/2335"}