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feat: add TypeScript 6 support #2774

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7bc63d0
feat(openapi-typescript): add TypeScript 6 support
Apr 15, 2026
a749a52
fix(openapi-typescript-helpers): preserve built-in objects in Readabl…
Apr 15, 2026
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9 changes: 9 additions & 0 deletions .changeset/widen-typescript-peer-dep.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
---
"openapi-typescript": patch
"openapi-typescript-helpers": patch
---

feat: add TypeScript 6 support

- Widen peer dep to `^5.x || ^6.x`
- Fix `Readable<T>` and `Writable<T>` to preserve built-in objects (Date, RegExp, functions) that now match `extends object` in TS6
2 changes: 1 addition & 1 deletion packages/openapi-typescript-helpers/package.json
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Expand Up @@ -34,6 +34,6 @@
"lint:ts": "tsc --noEmit"
},
"devDependencies": {
"typescript": "5.9.3"
"typescript": "6.0.2"
}
}
20 changes: 12 additions & 8 deletions packages/openapi-typescript-helpers/src/index.ts
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Expand Up @@ -223,9 +223,11 @@ export type Readable<T> =
? Readable<U>
: T extends (infer E)[]
? Readable<E>[]
: T extends object
? { [K in keyof T as NonNullable<T[K]> extends $Write<any> ? never : K]: Readable<T[K]> }
: T;
: T extends Date | RegExp | ((...args: never[]) => unknown)
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@benjamineckstein benjamineckstein Apr 15, 2026

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In TypeScript 6, Date extends object now evaluates to true (it was false in TS5). Without this guard, Readable<T> would structurally expand Date fields into { toString: {}; toDateString: {}; ... } instead of preserving the Date type — making any schema containing Date fields incompatible with itself when accessed through FetchResponse.

This guard preserves built-in objects (Date, RegExp, functions) by matching them before the generic T extends object branch. It's backward compatible with TS5 since these types were never matched by T extends object there.

? T
: T extends object
? { [K in keyof T as NonNullable<T[K]> extends $Write<any> ? never : K]: Readable<T[K]> }
: T;

/**
* Resolve type for writing (requests): strips $Read properties, unwraps $Write
Expand All @@ -240,8 +242,10 @@ export type Writable<T> =
? Writable<U>
: T extends (infer E)[]
? Writable<E>[]
: T extends object
? { [K in keyof T as NonNullable<T[K]> extends $Read<any> ? never : K]: Writable<T[K]> } & {
[K in keyof T as NonNullable<T[K]> extends $Read<any> ? K : never]?: never;
}
: T;
: T extends Date | RegExp | ((...args: never[]) => unknown)
? T
: T extends object
? { [K in keyof T as NonNullable<T[K]> extends $Read<any> ? never : K]: Writable<T[K]> } & {
[K in keyof T as NonNullable<T[K]> extends $Read<any> ? K : never]?: never;
}
: T;
2 changes: 1 addition & 1 deletion packages/openapi-typescript/package.json
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Expand Up @@ -59,7 +59,7 @@
"version": "pnpm run build"
},
"peerDependencies": {
"typescript": "^5.x"
"typescript": "^5.x || ^6.x"
},
"dependencies": {
"@redocly/openapi-core": "^1.34.6",
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89 changes: 69 additions & 20 deletions pnpm-lock.yaml
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