fix(forms): report forbidden 2way bindings on when FormField is applied

We were already reporting regular bindings but not 2way.

fixes #70219

packages/compiler-cli/src/ngtsc/typecheck/src/oob.ts

@@ -625,6 +625,8 @@ export class OutOfBandDiagnosticRecorderImpl implements OutOfBandDiagnosticRecor
         name = `[${node.name}]`;
       } else if (node.type === BindingType.Attribute) {
         name = `[attr.${node.name}]`;
+      } else if (node.type === BindingType.TwoWay) {
+        name = `[(${node.name})]`;
       } else {
         // We shouldn't hit this, but we have this logic as a fallback.
         name = node.name;

packages/compiler-cli/test/ngtsc/signal_forms_spec.ts

@@ -480,6 +480,31 @@ runInEachFileSystem(() => {
       );
     });
 
+    it('should report unsupported two-way bindings on a field', () => {
+      env.write(
+        'test.ts',
+        `
+          import {Component, signal} from '@angular/core';
+          import {FormField, form} from '@angular/forms/signals';
+
+          @Component({
+            template: '<input type="number" [formField]="f" [(max)]="maxLength"/>',
+            imports: [FormField]
+          })
+          export class Comp {
+            f = form(signal(''));
+            maxLength = 10;
+          }
+        `,
+      );
+
+      const diags = env.driveDiagnostics();
+      expect(diags.length).toBe(1);
+      expect(extractMessage(diags[0])).toBe(
+        `Binding to '[(max)]' is not allowed on nodes using the '[formField]' directive`,
+      );
+    });
+
     it('should report unsupported property bindings on a field with a custom control', () => {
       env.write(
         'test.ts',

packages/compiler/src/typecheck/ops/signal_forms.ts

@@ -429,6 +429,8 @@ export function checkUnsupportedFieldBindings(
       unsupportedBindingFields.has(input.name.toLowerCase())
     ) {
       tcb.oobRecorder.formFieldUnsupportedBinding(tcb.id, input);
+    } else if (input.type === BindingType.TwoWay && unsupportedBindingFields.has(input.name)) {
+      tcb.oobRecorder.formFieldUnsupportedBinding(tcb.id, input);
     }
   }