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fix(common): expand type for "ngForOf" input to work with strict null checks (#31371)

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Currently the `ngForOf` input accepts `null` or `undefined` as valid
values. Although when using strict template input type checking
(which will be supported by `ngtsc`), passing `null` or `undefined`
with strict null checks enabled causes a type check failure because
the type for the `ngForOf` input becomes too strict if strict null checks
are enabled. The type of the input needs to be expanded to also accept
`null` or `undefined` to behave consistently regardless of the
`strictNullChecks` flag.

This is necessary because whenever strict input type checking is enabled
by default, most of the Angular projects that use `*ngFor` with the async pipe
will either need to disable template type checking or strict null checks
because the `async` pipe returns `null` if the observable hasn't been
emitted yet.

See for example how this affects the `angular/components` repository and
how much bloat the workaround involves: https://github.com/angular/components/pull/16373/files#r296942696.

PR Close #31371
This commit is contained in:
Paul Gschwendtner
2019-10-03 18:31:28 +02:00
committed by Alex Rickabaugh
parent fee28e20bb
commit c1bb88603e
5 changed files with 12 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
packages/common/src/directives/ng_for_of.ts
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@ -129,7 +129,7 @@ export class NgForOf<T> implements DoCheck {
* [template input variable](guide/structural-directives#template-input-variable).
*/
@Input()
set ngForOf(ngForOf: NgIterable<T>) {
set ngForOf(ngForOf: NgIterable<T>|undefined|null) {
this._ngForOf = ngForOf;
this._ngForOfDirty = true;
}
@ -165,8 +165,7 @@ export class NgForOf<T> implements DoCheck {
get ngForTrackBy(): TrackByFunction<T> { return this._trackByFn; }
// TODO(issue/24571): remove '!'.
private _ngForOf !: NgIterable<T>;
private _ngForOf: NgIterable<T>|undefined|null = null;
private _ngForOfDirty: boolean = true;
private _differ: IterableDiffer<T>|null = null;
// TODO(issue/24571): remove '!'.
@ -219,8 +218,11 @@ export class NgForOf<T> implements DoCheck {
(item: IterableChangeRecord<any>, adjustedPreviousIndex: number | null,
currentIndex: number | null) => {
if (item.previousIndex == null) {
// NgForOf is never "null" or "undefined" here because the differ detected
// that a new item needs to be inserted from the iterable. This implies that
// there is an iterable value for "_ngForOf".
const view = this._viewContainer.createEmbeddedView(
this._template, new NgForOfContext<T>(null !, this._ngForOf, -1, -1),
this._template, new NgForOfContext<T>(null !, this._ngForOf !, -1, -1),
currentIndex === null ? undefined : currentIndex);
const tuple = new RecordViewTuple<T>(item, view);
insertTuples.push(tuple);
@ -243,7 +245,7 @@ export class NgForOf<T> implements DoCheck {
const viewRef = <EmbeddedViewRef<NgForOfContext<T>>>this._viewContainer.get(i);
viewRef.context.index = i;
viewRef.context.count = ilen;
viewRef.context.ngForOf = this._ngForOf;
viewRef.context.ngForOf = this._ngForOf !;
}
changes.forEachIdentityChange((record: any) => {