fix(runtime): stop immediate re-renders for reflected props when null !== undefined (#6404)

* fix: local (same-file) class inheritance search

* fix(runtime): stop immediate re-renders for null !== undefined

* chore: add test

* chore: lint

---------

Co-authored-by: John Jenkins <john.jenkins@nanoporetech.com>

Author: johnjenkins

src/runtime/proxy-component.ts

@@ -344,7 +344,7 @@ export const proxyComponent = (
           // test whether this property either has no 'getter' or if it does, does it also have a 'setter'
           // before attempting to write back to component props
           newValue = newValue === null && typeof this[propName] === 'boolean' ? (false as any) : newValue;
-          if (newValue !== this[propName] && (!propDesc.get || !!propDesc.set)) {
+          if (newValue != this[propName] && (!propDesc.get || !!propDesc.set)) {
             this[propName] = newValue;
           }
         });

src/runtime/test/prop-warnings.spec.tsx

@@ -125,4 +125,28 @@ describe('prop', () => {
 
     expect(spy).not.toHaveBeenCalled();
   });
+
+  it('should not show warning setting reflected prop to undefined', async () => {
+    @Component({ tag: 'cmp-a' })
+    class CmpA {
+      @Prop({ reflect: true }) a = 1;
+
+      render() {
+        return `${this.a ? this.a : ''}`;
+      }
+    }
+
+    const { root, waitForChanges } = await newSpecPage({
+      components: [CmpA],
+      html: `<cmp-a></cmp-a>`,
+    });
+
+    expect(root).toEqualHtml('<cmp-a a="1">1</cmp-a>');
+
+    root.a = undefined;
+    await waitForChanges();
+
+    expect(root).toEqualHtml('<cmp-a></cmp-a>');
+    expect(spy).not.toHaveBeenCalled();
+  });
 });