Allows a directive to use the expression passed directly to a property
as a guard instead of filtering the type through a type expression.
This more accurately matches the intent of the ngIf usage of its template
enabling better type inference.
Moved NgIf to using this type of guard instead of a function guard.
Closes: #20967
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
BREAKING CHANGE: the compiler option `enableLegacyTemplate` is now disabled by default as the `<template>` element has been deprecated since v4. Use `<ng-template>` instead. The option `enableLegacyTemplate` and the `<template>` element will both be removed in Angular v6.
PR Close#18756
Only one h1 is allowed per document, and this is provided by the template.
So we cannot have any h1 tags (or `#` markdown shorthand) in any API docs.
Closes#16193
* feat(common): support `as` syntax in template/* bindings
Closes#15020
Showing the new and the equivalent old syntax.
- `*ngIf="exp as var1”`
=> `*ngIf="exp; let var1 = ngIf”`
- `*ngFor="var item of itemsStream |async as items”`
=> `*ngFor="var item of itemsStream |async; let items = ngForOf”`
* feat(common): convert ngIf to use `*ngIf="exp as local“` syntax
* feat(common): convert ngForOf to use `*ngFor=“let i of exp as local“` syntax
* feat(common): expose NgForOfContext and NgIfContext
