f18e1739b8
Consider the case in which `FormBuilder` is used to construct a group with an optional field:
```
const controls = { name: fb.control('') };
const foo: FormGroup<{
name: FormControl<string | null>;
address?: FormControl<string | null>;
}> = fb.group<{
name: FormControl<string | null>;
address?: FormControl<string | null>;
}>(controls);
```
Today, with fully strict TypeScript settings, the above will not compile:
```
Types of property 'controls' are incompatible.
Type '{ name: FormControl<string | null>; address?: FormControl<FormGroup<SubFormControls> | null | undefined> | undefined; }' is not assignable to type '{ name: FormControl<string | null>; address?: FormGroup<SubFormControls> | undefined; }'.
```
Notice that the `fb.group(...)` is calculating the following type for address: `address?: FormControl<FormGroup<string|null>`. This is clearly wrong -- an extraneous `FormControl` has been added!
This is coming from the calculation of the result type of `fb.group(...)`. In the type definition, if we cannot detect the outer control type, [we assume it's just an unwrapped value, and automatically wrap it in `FormControl`](https://github.com/angular/angular/blob/14.0.0/packages/forms/src/form_builder.ts#L66).
Because the optional `{address?: FormControl<string|null>}` implicitly makes the RHS have type `FormControl<string|null>|undefined`, [the relevant condition is not satisfied](https://github.com/angular/angular/blob/14.0.0/packages/forms/src/form_builder.ts#L55). In particular, the condition expects just `FormGroup<T>`, not `FormGroup<T>|undefined`. So we assume `T` is a value type, and it gets wrapped with `FormControl`.
The solution is to add the cases where `undefined` is included in the union type when detecting which control `T` is (if any).
PR Close #46253
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