This commit separates `InputSignal` for input signals with transforms.
The reason being that most of the time, signal inputs are not using
transforms and the generics are rather confusing.
Especially for users with inferred types displayed in their IDEs, the
input signal types are seemingly complex, even if no transform is used.
For this reason, we are introducing a new type called
`InputSignalWithTransform`. This type will be used for inputs with
transforms, while non-transform inputs just use `InputSignal`.
A notable fact is that `InputSignal` extends `InputSignalWithTransform`,
with the "identity transform". i.e. there is no transform. This allows
us to share the code for input signals. In practice, we don't expect
users to pass around `InputSignal`'s anyway.
PR Close#54233
Enables signal inputs for existing Zone based components.
This is a next step we are taking to bring signal inputs earlier to the Angular community.
The goal is to enable early access for the ecosystem to signal inputs, while we are continuing
development of full signal components as outlined in the RFC. This will allow the ecosystem
to start integrating signals more deeply, prepare for future migrations, and improves code quality
and DX for existing components (especially for OnPush).
Based on our work on full signal components, we've gathered more information and learned
new things. We've improved the API by introducing a way to intuitively declare required inputs,
as well as improved the API around initial values. We even support non-primitive initial values
as the first argument to the `input` function now.
```ts
@Directive({..})
export class MyDir {
firstName = input<string>(); // string|undefined
lastName = input.required<string>(); // string
age = input(0); // number
```
PR Close#53872
Adds tests that allow us to ensure that the `input` API works as
expected and that resulting return types match our expectations- without
silently regressing in the future, or missing potential edge-cases.
Testing signatures is hard because of covariance and contravariance,
especially when it comes to the different semantics of `ReadT` and
`WriteT` of input signals. We enable reliable testing by validating the
`d.ts` of the "fake directive class". This ensures clear results,
compared to relying on e.g. type assertions that might
accidentally/silently pass due to covariance/contravariance or
biavariance in the type system.
PR Close#53571
Paul Gschwendtner