fix(core): treat `[class]` and `[className]` as unrelated bindings (#35668)

Before this change `[class]` and `[className]` were both converted into `ɵɵclassMap`. The implication of this is that at runtime we could not differentiate between the two and as a result we treated `@Input('class')` and `@Input('className)` as equivalent.

This change makes `[class]` and `[className]` distinct. The implication of this is that `[class]` becomes `ɵɵclassMap` instruction but  `[className]` becomes `ɵɵproperty' instruction. This means that `[className]` will no longer participate in styling and will overwrite the DOM `class` value.

Fix #35577

PR Close #35668

packages/compiler/src/render3/view/styling_builder.ts

@@ -202,8 +202,7 @@ export class StylingBuilder {
     let binding: BoundStylingEntry|null = null;
     const prefix = name.substring(0, 6);
     const isStyle = name === 'style' || prefix === 'style.' || prefix === 'style!';
-    const isClass = !isStyle &&
-        (name === 'class' || name === 'className' || prefix === 'class.' || prefix === 'class!');
+    const isClass = !isStyle && (name === 'class' || prefix === 'class.' || prefix === 'class!');
     if (isStyle || isClass) {
       const isMapBased = name.charAt(5) !== '.';         // style.prop or class.prop makes this a no
       const property = name.substr(isMapBased ? 5 : 6);  // the dot explains why there's a +1

packages/core/src/render3/instructions/property.ts

@@ -53,6 +53,5 @@ export function setDirectiveInputsWhichShadowsStyling(
   const inputs = tNode.inputs !;
   const property = isClassBased ? 'class' : 'style';
   // We support both 'class' and `className` hence the fallback.
-  const stylingInputs = inputs[property] || (isClassBased && inputs['className']);
-  setInputsForProperty(tView, lView, stylingInputs, property, value);
+  setInputsForProperty(tView, lView, inputs[property], property, value);
 }

packages/core/src/render3/instructions/shared.ts

@@ -907,7 +907,7 @@ function initializeInputAndOutputAliases(tView: TView, tNode: TNode): void {
   }
 
   if (inputsStore !== null) {
-    if (inputsStore.hasOwnProperty('class') || inputsStore.hasOwnProperty('className')) {
+    if (inputsStore.hasOwnProperty('class')) {
       tNode.flags |= TNodeFlags.hasClassInput;
     }
     if (inputsStore.hasOwnProperty('style')) {

packages/core/test/acceptance/styling_spec.ts

@@ -1129,17 +1129,17 @@ describe('styling', () => {
   });
 
   onlyInIvy('only ivy combines static and dynamic class-related attr values')
-      .it('should write to a `className` input binding, when static `class` is present', () => {
+      .it('should write combined class attribute and class binding to the class input', () => {
         @Component({
           selector: 'comp',
           template: `{{className}}`,
         })
         class Comp {
-          @Input() className: string = '';
+          @Input('class') className: string = '';
         }
 
         @Component({
-          template: `<comp class="static" [className]="'my-className'"></comp>`,
+          template: `<comp class="static" [class]="'my-className'"></comp>`,
         })
         class App {
         }
@@ -1150,32 +1150,6 @@ describe('styling', () => {
         expect(fixture.debugElement.nativeElement.firstChild.innerHTML).toBe('static my-className');
       });
 
-  onlyInIvy('in Ivy [class] and [className] bindings on the same element are not allowed')
-      .it('should throw an error in case [class] and [className] bindings are used on the same element',
-          () => {
-            @Component({
-              selector: 'comp',
-              template: `{{class}} - {{className}}`,
-            })
-            class Comp {
-              @Input() class: string = '';
-              @Input() className: string = '';
-            }
-            @Component({
-              template: `<comp [class]="'my-class'" [className]="'className'"></comp>`,
-            })
-            class App {
-            }
-
-            TestBed.configureTestingModule({declarations: [Comp, App]});
-            expect(() => {
-              const fixture = TestBed.createComponent(App);
-              fixture.detectChanges();
-            })
-                .toThrowError(
-                    '[class] and [className] bindings cannot be used on the same element simultaneously');
-          });
-
   onlyInIvy('only ivy persists static class/style attrs with their binding counterparts')
       .it('should write to a `class` input binding if there is a static class value and there is a binding value',
           () => {
@@ -3475,6 +3449,44 @@ describe('styling', () => {
           expectClass(cmp1).toEqual({foo: true, bar: true});
           expectClass(cmp2).toEqual({foo: true, bar: true});
         });
+
+    it('should not bind [class] to @Input("className")', () => {
+      @Component({
+        selector: 'my-cmp',
+        template: `className = {{className}}`,
+      })
+      class MyCmp {
+        @Input()
+        className: string = 'unbound';
+      }
+      @Component({template: `<my-cmp [class]="'bound'"></my-cmp>`})
+      class MyApp {
+      }
+
+      TestBed.configureTestingModule({declarations: [MyApp, MyCmp]});
+      const fixture = TestBed.createComponent(MyApp);
+      fixture.detectChanges();
+      expect(fixture.nativeElement.textContent).toEqual('className = unbound');
+    });
+
+    it('should not bind class to @Input("className")', () => {
+      @Component({
+        selector: 'my-cmp',
+        template: `className = {{className}}`,
+      })
+      class MyCmp {
+        @Input()
+        className: string = 'unbound';
+      }
+      @Component({template: `<my-cmp class="bound"></my-cmp>`})
+      class MyApp {
+      }
+
+      TestBed.configureTestingModule({declarations: [MyApp, MyCmp]});
+      const fixture = TestBed.createComponent(MyApp);
+      fixture.detectChanges();
+      expect(fixture.nativeElement.textContent).toEqual('className = unbound');
+    });
   });
 });