Paul Gschwendtner a9242c4fc2 refactor(core): template-var-assignment migration incorrectly warns (#30026)
Currently the `template-var-assignment` migration incorrectly warns if
the template writes to a property in the component that has the same
`ast.PropertyWrite´ name as a template input variable but different
receiver. e.g.

```html
<!-- "someProp.element" will be incorrectly reported as template variable assignment -->
<button *ngFor="let element of list" (click)="someProp.element = null">Reset</button>
```

Similarly if an output writes to a component property with the same name as a
template input variable, but the expression is within a different template scope,
the schematic currently incorrectly warns. e.g.

```html
<button *ngFor="let element of list">{{element}}</button>

<!-- The "element = null" expression does not refer to the "element" template input variable -->
<button (click)="element = null"></button>
```

PR Close #30026
2019-04-22 11:16:19 -07:00
..

Assignments to template variables

With Ivy, assignments to template variables are no longer supported as template variables are effectively constants.

This means that assignments to template variables will break your application once Ivy is enabled by default. For example:

<button *ngFor="let option of options"
       (click)="option = 'newButtonText'">
  {{ option }}
</button>

In the example from above, a value is assigned to the option template variable on click. This will ultimately break your application and therefore the logic needs to be adjusted to not update the option variable, but rather the given element in the options array:

<button *ngFor="let option of options; let idx = index"
       (click)="options[idx] = 'newButtonText'">
  {{ option }}
</button>