feat(material/chips): update chip-list describedby to match input

Fixes #16209: ExpressionChangedAfterItHasBeenCheckedError that occurs when chip-lists are content-projected into a mat-form-field

Author: RobertAKARobin

src/material/chips/chip-list.ts

@@ -78,7 +78,6 @@ export class MatChipListChange {
   exportAs: 'matChipList',
   host: {
     '[attr.tabindex]': 'disabled ? null : _tabIndex',
-    '[attr.aria-describedby]': '_ariaDescribedby || null',
     '[attr.aria-required]': 'role ? required : null',
     '[attr.aria-disabled]': 'disabled.toString()',
     '[attr.aria-invalid]': 'errorState',
@@ -144,9 +143,6 @@ export class MatChipList
   /** Uid of the chip list */
   _uid: string = `mat-chip-list-${nextUniqueId++}`;
 
-  /** The aria-describedby attribute on the chip list for improved a11y. */
-  _ariaDescribedby: string;
-
   /** Tab index for the chip list. */
   _tabIndex = 0;
 
@@ -177,6 +173,12 @@ export class MatChipList
     return this.empty ? null : 'listbox';
   }
 
+  /**
+   * Implemented as part of MatFormFieldControl.
+   * @docs-private
+   */
+  @Input('aria-describedby') userAriaDescribedBy: string;
+
   /** An object used to control when error messages are shown. */
   @Input() override errorStateMatcher: ErrorStateMatcher;
 
@@ -455,7 +457,11 @@ export class MatChipList
    * @docs-private
    */
   setDescribedByIds(ids: string[]) {
-    this._ariaDescribedby = ids.join(' ');
+    if (ids.length) {
+      this._elementRef.nativeElement.setAttribute('aria-describedby', ids.join(' '));
+    } else {
+      this._elementRef.nativeElement.removeAttribute('aria-describedby');
+    }
   }
 
   // Implemented as part of ControlValueAccessor.

tools/public_api_guard/material/chips.md

@@ -181,7 +181,6 @@ export interface MatChipInputEvent {
 export class MatChipList extends _MatChipListBase implements MatFormFieldControl<any>, ControlValueAccessor, AfterContentInit, DoCheck, OnInit, OnDestroy, CanUpdateErrorState {
     constructor(_elementRef: ElementRef<HTMLElement>, _changeDetectorRef: ChangeDetectorRef, _dir: Directionality, _parentForm: NgForm, _parentFormGroup: FormGroupDirective, _defaultErrorStateMatcher: ErrorStateMatcher, ngControl: NgControl);
     _allowFocusEscape(): void;
-    _ariaDescribedby: string;
     ariaOrientation: 'horizontal' | 'vertical';
     _blur(): void;
     readonly change: EventEmitter<MatChipListChange>;
@@ -255,6 +254,7 @@ export class MatChipList extends _MatChipListBase implements MatFormFieldControl
     _uid: string;
     protected _updateFocusForDestroyedChips(): void;
     protected _updateTabIndex(): void;
+    userAriaDescribedBy: string;
     _userTabIndex: number | null;
     get value(): any;
     set value(value: any);
@@ -264,7 +264,7 @@ export class MatChipList extends _MatChipListBase implements MatFormFieldControl
     // (undocumented)
     writeValue(value: any): void;
     // (undocumented)
-    static ɵcmp: i0.ɵɵComponentDeclaration<MatChipList, "mat-chip-list", ["matChipList"], { "errorStateMatcher": "errorStateMatcher"; "multiple": "multiple"; "compareWith": "compareWith"; "value": "value"; "required": "required"; "placeholder": "placeholder"; "disabled": "disabled"; "ariaOrientation": "aria-orientation"; "selectable": "selectable"; "tabIndex": "tabIndex"; }, { "change": "change"; "valueChange": "valueChange"; }, ["chips"], ["*"]>;
+    static ɵcmp: i0.ɵɵComponentDeclaration<MatChipList, "mat-chip-list", ["matChipList"], { "userAriaDescribedBy": "aria-describedby"; "errorStateMatcher": "errorStateMatcher"; "multiple": "multiple"; "compareWith": "compareWith"; "value": "value"; "required": "required"; "placeholder": "placeholder"; "disabled": "disabled"; "ariaOrientation": "aria-orientation"; "selectable": "selectable"; "tabIndex": "tabIndex"; }, { "change": "change"; "valueChange": "valueChange"; }, ["chips"], ["*"]>;
     // (undocumented)
     static ɵfac: i0.ɵɵFactoryDeclaration<MatChipList, [null, null, { optional: true; }, { optional: true; }, { optional: true; }, null, { optional: true; self: true; }]>;
 }