refactor(angular/input): support signal-based input accessor (#2394)

Expands the `SBB_INPUT_VALUE_ACCESSOR` to support a signal-based accessor.

src/angular/input/input-value-accessor.ts

@@ -1,11 +1,11 @@
-import { InjectionToken } from '@angular/core';
+import { InjectionToken, WritableSignal } from '@angular/core';
 
 /**
  * This token is used to inject the object whose value should be set into `InputDirective`.
  * If none is provided, the native `HTMLInputElement` is used. Directives can provide
  * themselves for this token, in order to make `InputDirective` delegate the getting and setting of the
  * value to them.
  */
-export const SBB_INPUT_VALUE_ACCESSOR = new InjectionToken<{ value: any }>(
+export const SBB_INPUT_VALUE_ACCESSOR = new InjectionToken<{ value: any | WritableSignal<any> }>(
   'SBB_INPUT_VALUE_ACCESSOR',
 );

src/angular/input/input.ts

@@ -5,14 +5,17 @@ import {
   AfterViewInit,
   Directive,
   DoCheck,
+  effect,
   ElementRef,
   HostListener,
   inject,
   Input,
+  isSignal,
   NgZone,
   numberAttribute,
   OnChanges,
   OnDestroy,
+  WritableSignal,
 } from '@angular/core';
 import { FormGroupDirective, NgControl, NgForm } from '@angular/forms';
 import { SbbErrorStateMatcher, _ErrorStateTracker } from '@sbb-esta/angular/core';
@@ -68,6 +71,7 @@ export class SbbInput
   private _autofillMonitor = inject(AutofillMonitor);
   private _previousNativeValue: any;
   private _inputValueAccessor: { value: any };
+  private _signalBasedValueAccessor?: { value: WritableSignal<any> };
   private _errorStateTracker: _ErrorStateTracker;
   ngControl: NgControl = inject(NgControl, { optional: true, self: true })!;
 
@@ -194,13 +198,19 @@ export class SbbInput
    */
   @Input()
   get value(): string {
-    return this._inputValueAccessor.value;
+    return this._signalBasedValueAccessor
+      ? this._signalBasedValueAccessor.value()
+      : this._inputValueAccessor.value;
   }
   // Accept `any` to avoid conflicts with other directives on `<input>` that may
   // accept different types.
   set value(value: any) {
     if (value !== this.value) {
-      this._inputValueAccessor.value = value;
+      if (this._signalBasedValueAccessor) {
+        this._signalBasedValueAccessor.value.set(value);
+      } else {
+        this._inputValueAccessor.value = value;
+      }
       this.stateChanges.next();
     }
   }
@@ -255,15 +265,23 @@ export class SbbInput
     const parentForm = inject(NgForm, { optional: true })!;
     const parentFormGroup = inject(FormGroupDirective, { optional: true })!;
     const defaultErrorStateMatcher = inject(SbbErrorStateMatcher);
-    const inputValueAccessor = inject(SBB_INPUT_VALUE_ACCESSOR, { optional: true, self: true })!;
+    const accessor = inject(SBB_INPUT_VALUE_ACCESSOR, { optional: true, self: true })!;
     const ngZone = inject(NgZone);
 
     const element = this._elementRef.nativeElement;
     const nodeName = element.nodeName.toLowerCase();
 
-    // If no input value accessor was explicitly specified, use the element as the input value
-    // accessor.
-    this._inputValueAccessor = inputValueAccessor || element;
+    if (accessor) {
+      if (isSignal(accessor.value)) {
+        this._signalBasedValueAccessor = accessor;
+      } else {
+        this._inputValueAccessor = accessor;
+      }
+    } else {
+      // If no input value accessor was explicitly specified, use the element as the input value
+      // accessor.
+      this._inputValueAccessor = element;
+    }
 
     this._previousNativeValue = this.value;
 
@@ -290,6 +308,14 @@ export class SbbInput
         ? 'sbb-native-select-multiple'
         : 'sbb-native-select';
     }
+
+    if (this._signalBasedValueAccessor) {
+      effect(() => {
+        // Read the value so the effect can register the dependency.
+        this._signalBasedValueAccessor!.value();
+        this.stateChanges.next();
+      });
+    }
   }
 
   ngAfterViewInit() {