XYZ-450: Fix label control logic and add tests for optional struct presence

projects/ng-thrift/src/lib/components/thrift-editor/components/struct-form/struct-form.component.spec.ts

@@ -0,0 +1,58 @@
+import { Component, provideZonelessChangeDetection } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+import { FormControl, ReactiveFormsModule } from '@angular/forms';
+
+import { ThriftData } from '../../../../models';
+import { ThriftAstMetadata } from '../../../../types';
+
+import { StructFormComponent } from './struct-form.component';
+
+@Component({
+    imports: [ReactiveFormsModule, StructFormComponent],
+    template: `<v-struct-form [data]="data" [formControl]="control" />`,
+})
+class StructFormHost {
+    control = new FormControl<Record<string, unknown>>({});
+    metadata: ThriftAstMetadata[] = [
+        { name: 'test', path: 'test.thrift', ast: { struct: { Parent: [], Empty: [] } } },
+    ];
+    data = new ThriftData<string, 'struct'>(
+        this.metadata,
+        'test',
+        'Empty',
+        { name: 'empty', type: 'Empty', option: 'optional' },
+        new ThriftData(this.metadata, 'test', 'Parent'),
+    );
+}
+
+describe('Optional struct presence', () => {
+    beforeEach(() => {
+        TestBed.configureTestingModule({ providers: [provideZonelessChangeDetection()] });
+    });
+
+    it('checks an empty struct and preserves its value when toggled', async () => {
+        const fixture = TestBed.createComponent(StructFormHost);
+        await fixture.whenStable();
+        const checkbox: HTMLInputElement = fixture.nativeElement.querySelector('input');
+
+        expect(checkbox.checked).toBe(true);
+        expect(fixture.componentInstance.control.value).toEqual({});
+
+        checkbox.click();
+        await fixture.whenStable();
+        expect(fixture.componentInstance.control.value).toBeNull();
+
+        checkbox.click();
+        await fixture.whenStable();
+        expect(fixture.componentInstance.control.value).toEqual({});
+    });
+
+    it.each([null, undefined])('leaves an absent struct unchecked (%s)', async (value) => {
+        const fixture = TestBed.createComponent(StructFormHost);
+        fixture.componentInstance.control.setValue(value);
+        await fixture.whenStable();
+
+        const checkbox: HTMLInputElement = fixture.nativeElement.querySelector('input');
+        expect(checkbox.checked).toBe(false);
+    });
+});

projects/ng-thrift/src/lib/components/thrift-editor/components/struct-form/struct-form.component.ts

@@ -116,7 +116,7 @@ export class StructFormComponent<T extends Record<string, unknown>>
 
     handleIncomingValue(value: T) {
         this.control.patchValue(value as never, { emitEvent: false });
-        this.setLabelControl(!!(value && Object.keys(value).length));
+        this.setLabelControl(!isNil(value));
     }
 
     override validate(_control: AbstractControl): ValidationErrors | null {