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.d.ts generation, TypeScript 5.7

🕗 Version & Regression Information

• This changed between versions 5.6.3 and 5.7.1-rc

⏯ Playground Link

Note: look at the ".D.TS" tab in the playground

https://www.typescriptlang.org/play/?ts=5.7.1-rc#code/KYDwDg9gTgLgBAYwDYEMDOa4DFoFsDCEAdjFBEgDwAqAfHAN4BQccAbikgK7ACEAXHCoBuRgF9GoSLESoM2PAHEynMNTpMWCYqXJp+gkeMbJ0mHFFwAhTgEskAE2BQGzOAHNlqqnFAxgRe0x6URoACldNbTIkNAEqABpXAEoBc1wlCBUKegBtAGk4GyI4AGtgAE8IADNBAF1UvEISaOp82poQlxYWKGAYTihiok4kJB4RFnEjLSI0eCqAIzgAXjgiYAB3eQtrO0coUKSRRgB6E7gAOnsLmExe-sG4GHKwYELMIq0oXoR4IrgAKwXADsFwAjABaKAIOCZGBgTgwPinc4sNIZLL0ewoGAoARzKBFNw5WpwAA+axGSBCKLgAElikCAGwXADMyLO3XRnmy2NxDQsTR0lAJRJJ5Mpow6NAk4Gg804RF+NmI7j6GLAhy6cHuA2KiwuHkymo03T5eLg4vQcFFRGJpIpw1GiUmRzEjFpAHUbDAABb-P02TBVOzAeJPX1vZ6vWE1AAGbnVnkOcfecA4GxQ5UwXx+MHDaAgtMDmBQCAQwDkGazmA20BKaAujETMA1hwuM2FjfNF3YXGAQiAA

💻 Code

export class FormControl<T> { value!: T; } export class FormGroup<T> { controls!: T; } class FormBuilder { group<T extends {}>( controls: T, ): FormGroup<{[K in keyof T]: FormControl<T[K]>}> { return null!; } } const fb = new FormBuilder(); export function getGroup() { return fb.group({ data: [] as string[] | null, }); }

🙁 Actual behavior

Given the code above, TypeScript 5.7 produces a .d.ts file that looks like this:

export declare function getGroup(fb: FormBuilder): FormGroup<{ data: string[] | null; // <----- Incorrect }>; 

🙂 Expected behavior

It should produce something like this:

export declare function getGroup(fb: FormBuilder): FormGroup<{ data: FormControl<string[] | null>; }>; 

Additional information about the issue

Source code of Angular's FormBuilder: https://github.com/angular/angular/blob/main/packages/forms/src/form_builder.ts