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fix(platform-browser): debug element query predicates not compatible …

…with strictFunctionTypes (#30993)

Currently developers can use the `By` class to construct common
`DebugElement` query predicates. e.g. `By.directive(MyDirective)`.

The `directive()` and `all()` predicates are currently returning
a predicate that works for `DebugElement` nodes. This return type
is too strict since the predicate is not specific to `DebugElement`
instances and can also apply to `DebugNode` instances.

Meaning that developers are currently able to use the `directive()`
predicate when using `queryAllNodes()`. This is a common practice
but will break when the project is compiled with TypeScript's
`--strictFunctionTypes` flag as the `DebugElement` predicate type
is not assignable to predicates for `DebugNode`. In order to make
these predicates usable with `--strictFuntionTypes` enabled, we
adjust the predicate type to reflect what is actually needed for
evaluation of the predicate.

PR Close #30993
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devversion authored and mhevery committed Jun 14, 2019
1 parent 647d7bd commit 10a1e1974b816ebb979dc10586b160ee07ad8356
@@ -6,7 +6,7 @@
* found in the LICENSE file at

import {DebugElement, Predicate, Type} from '@angular/core';
import {DebugElement, DebugNode, Predicate, Type} from '@angular/core';
import {getDOM} from '../../dom/dom_adapter';

@@ -18,14 +18,14 @@ import {getDOM} from '../../dom/dom_adapter';
export class By {
* Match all elements.
* Match all nodes.
* @usageNotes
* ### Example
* {@example platform-browser/dom/debug/ts/by/by.ts region='by_all'}
static all(): Predicate<DebugElement> { return (debugElement) => true; }
static all(): Predicate<DebugNode> { return () => true; }

* Match elements by the given CSS selector.
@@ -44,14 +44,14 @@ export class By {

* Match elements that have the given directive present.
* Match nodes that have the given directive present.
* @usageNotes
* ### Example
* {@example platform-browser/dom/debug/ts/by/by.ts region='by_directive'}
static directive(type: Type<any>): Predicate<DebugElement> {
return (debugElement) => debugElement.providerTokens !.indexOf(type) !== -1;
static directive(type: Type<any>): Predicate<DebugNode> {
return (debugNode) => debugNode.providerTokens !.indexOf(type) !== -1;
@@ -9,9 +9,9 @@ export declare class BrowserTransferStateModule {

export declare class By {
static all(): Predicate<DebugElement>;
static all(): Predicate<DebugNode>;
static css(selector: string): Predicate<DebugElement>;
static directive(type: Type<any>): Predicate<DebugElement>;
static directive(type: Type<any>): Predicate<DebugNode>;

export declare function disableDebugTools(): void;

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