Add support for TypeScript 6

[jansepke]

Description

please allow the new TypeScript 6 as a peer dependency for openapi-typescript

Proposal

add version 6 to typescript peer dependency

Extra

• I’m willing to open a PR (see CONTRIBUTING.md)

[yamafaktory]

Hi :),

I'm working on a company project where we've recently switched to TypeScript 6.

One issue we faced is the openapi-typescript-helpers package (0.1.0). In TypeScript 6, Date extends object evaluates to true, which was not the case in TypeScript 5. This causes Readable<T> to structurally expand Date fields into { toString: {}; toDateString: {}; ... } instead of preserving Date, making any schema type containing Date fields incompatible with itself when accessed through FetchResponse.

Currently the package provides:

type Readable<T> = T extends $Write<any> ? never
    : T extends $Read<infer U> ? 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;

What would be needed would be something in that vein:

type Readable<T> = T extends $Write<any> ? never
    : T extends $Read<infer U> ? Readable<U>
    : T extends (infer E)[] ? Readable<E>[]
    : T extends Date | RegExp | ((...args: never[]) => unknown) ? T  // preserve built-in objects
    : T extends object ? { [K in keyof T as NonNullable<T[K]> extends $Write<any> ? never : K]: Readable<T[K]>; }
    : T;

And then we have the same issue with Writable<T>.

[takaram]

This seems duplicate of #2550

[benjamineckstein]

PR #2773 widens the peer dependency to ^5.x || ^6.x — verified that build, tests, and lint all pass with no code changes needed.

This is a minimal, focused fix (just the peer dep range + changeset) compared to #2711 which also upgrades the monorepo's own TypeScript devDependency to v6.

[benjamineckstein]

Updated PR: #2774 — adds full TypeScript 6 support (peer dep widened to ^5.x || ^6.x, devDependency upgraded to 6.0.2, changeset included). Build, tests, and lint all pass.

[benjamineckstein]

PR #2774 now also includes the fix for Readable<T> and Writable<T> reported by @yamafaktory above — added a guard clause for Date | RegExp | functions before the T extends object branch in both types. Backward compatible with TS5.