Reset controlled .checked upon hydration

Author: sophiebits

packages/react-dom-bindings/src/client/ReactDOMInput.js

@@ -292,7 +292,7 @@ export function initInput(
     typeof checkedOrDefault !== 'symbol' &&
     !!checkedOrDefault;
 
-  if (isHydrating) {
+  if (isHydrating && checked == null) {
     // Detach .checked from .defaultChecked but leave user input alone
     node.checked = node.checked;
   } else {

packages/react-dom/src/__tests__/ReactDOMInput-test.js

@@ -1300,23 +1300,22 @@ describe('ReactDOMInput', () => {
 
     // Currently, we don't fire onChange when hydrating
     assertLog([]);
-    // Strangely, we leave `b` checked even though we rendered A with
-    // checked={true} and B with checked={false}. Arguably this is a bug.
-    expect(a.checked).toBe(false);
-    expect(b.checked).toBe(true);
+    // Instead, we reset the form to match React state and you lose the user's input.
+    expect(a.checked).toBe(true);
+    expect(b.checked).toBe(false);
     expect(c.checked).toBe(false);
     expect(isCheckedDirty(a)).toBe(true);
     expect(isCheckedDirty(b)).toBe(true);
     expect(isCheckedDirty(c)).toBe(true);
     assertInputTrackingIsCurrent(container);
 
-    // If we click on C now though...
+    // If we click on C now...
     await act(async () => {
       setUntrackedChecked.call(c, true);
       dispatchEventOnNode(c, 'click');
     });
 
-    // then since C's onClick doesn't set state, A becomes rechecked.
+    // there's no change.
     assertLog(['click c']);
     expect(a.checked).toBe(true);
     expect(b.checked).toBe(false);