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Structural directives can now specify a type guard that describes
what types can be inferred for an input expression inside the
directive's template.
NgIf was modified to declare an input guard on ngIf.
After this change, `fullTemplateTypeCheck` will infer that
usage of `ngIf` expression inside it's template is truthy.
For example, if a component has a property `person?: Person`
and a template of `<div *ngIf="person"> {{person.name}} </div>`
the compiler will no longer report that `person` might be null or
undefined.
The template compiler will generate code similar to,
```
if (NgIf.ngIfTypeGuard(instance.person)) {
instance.person.name
}
```
to validate the template's use of the interpolation expression.
Calling the type guard in this fashion allows TypeScript to infer
that `person` is non-null.
Fixes: #19756?
PR Close #20702
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| .. | ||
| diagnostics | ||
| metadata | ||
| transformers | ||
| extract_i18n_spec.ts | ||
| mocks.ts | ||
| ngc_spec.ts | ||
| ngtools_api_spec.ts | ||
| perform_watch_spec.ts | ||
| test_support.ts | ||