Angular compiler strips | null from signal input types in partial compilation .d.ts output

[thomaswinckell]

Which @angular/* package(s) are the source of the bug?

compiler

Is this a regression?

Yes

Description

When using input.required<T | null>() or input<T | null>() in a library built with ng-packagr (partial compilation mode), the Angular compiler strips | null from the generated .d.ts files.

Source:

a = input.required<T | null>();
b = input<T | null>();

Expected .d.ts (matches plain tsc --emitDeclarationOnly):

a: InputSignal<T | null>;
b: InputSignal<T | null | undefined>;

Actual .d.ts from Angular compiler (partial mode):

 a: _angular_core.InputSignal<T>; 
 b: _angular_core.InputSignal<T>;

Investigation:
I intercepted the in-memory .d.ts content from ng-packagr's file cache (before rollup-plugin-dts bundling) and confirmed | null was already missing at that stage. Plain tsc --emitDeclarationOnly on the same source produces correct types.

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (run ng version)

Angular 21.2.x, ng-packagr 21.2.0, TypeScript 5.9.3

Anything else?

A workaround is to force the type and not rely on type inference.
Example:

a: InputSignal<T | null> = input<T| null>();

[alxhub]

Does the tsconfig for the compliation have strictNullChecks: false perhaps?

[thomaswinckell]

Does the tsconfig for the compliation have strictNullChecks: false perhaps?

No, the tsconfig has strict: true and no strictNullChecks: false.
I even tried adding strictNullChecks: true on top of strict: true, just in case.

[JoostK]

Are you using ng-packagr "standalone", i.e. not through the CLI's builder? Its default tsconfig does not have strict/strictNullChecks enabled, you'd need a custom tsconfig and the --config option to reference that file for this to work. I have just verified that this makes things work as you expected.