@samitouri / QOS-React-2 / commits / 0f83a64eda

Regression test: Missing unmount after re-order (#20285)

Adds a regression test for a bug I found in the effects refactor. The bug was that reordering a child that contains passive effects would cause the child to "forget" that it contains passive effects. This is because when a Placement effect is scheduled by the reconciler, it would override all of the fiber's flags, including its "static" ones: ``` child.flags = Placement; ``` The problem is that we use a static flag to use a "static" flag to track that a fiber contains passive effects. So what happens is that when the tree is deleted, the unmount effect is never fired. In the new implementation, the fix is to add the Placement flag without overriding the rest of the bitmask: ``` child.flags |= Placement; ``` (The old implementation doesn't need to be changed because it does not use static flags for this purpose.)

Andrew Clark committed Nov 18, 2020 at 10:33 UTC 0f83a64eda73e93135b2d30531b10427fccc4c05

1 file changed +46

packages/react-reconciler/src/__tests__/ReactHooksWithNoopRenderer-test.js

+46

@@ -3370,4 +3370,50 @@ describe('ReactHooksWithNoopRenderer', () => {

3370 });

3371 expect(Scheduler).toHaveYielded(['Unmount layout B', 'Unmount passive B']);

3372 });

3373 +

3374 + it('regression: deleting a tree and unmounting its effects after a reorder', async () => {

3375 + const root = ReactNoop.createRoot();

3376 +

3377 + function Child({label}) {

3378 + useEffect(() => {

3379 + Scheduler.unstable_yieldValue('Mount ' + label);

3380 + return () => {

3381 + Scheduler.unstable_yieldValue('Unmount ' + label);

3382 + };

3383 + }, [label]);

3384 + return label;

3385 + }

3386 +

3387 + await act(async () => {

3388 + root.render(

3389 + <>

3390 + <Child key="A" label="A" />

3391 + <Child key="B" label="B" />

3392 + </>,

3393 + );

3394 + });

3395 + expect(Scheduler).toHaveYielded(['Mount A', 'Mount B']);

3396 +

3397 + await act(async () => {

3398 + root.render(

3399 + <>

3400 + <Child key="B" label="B" />

3401 + <Child key="A" label="A" />

3402 + </>,

3403 + );

3404 + });

3405 + expect(Scheduler).toHaveYielded([]);

3406 +

3407 + await act(async () => {

3408 + root.render(null);

3409 + });

3410 +

3411 + expect(Scheduler).toHaveYielded([

3412 + 'Unmount B',

3413 + // In the regression, the reorder would cause Child A to "forget" that it

3414 + // contains passive effects. Then when we deleted the tree, A's unmount

3415 + // effect would not fire.

3416 + 'Unmount A',

3417 + ]);

3418 + });

3419 });