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Warn if MutableSource snapshot is a function #18933

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Merged
merged 2 commits into from
May 21, 2020
Merged

Warn if MutableSource snapshot is a function #18933

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c82a507
Warn if MutableSource snapshot is a function
May 15, 2020
2c45e61
Replaced .warn with .error
May 21, 2020
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20 changes: 19 additions & 1 deletion packages/react-reconciler/src/ReactFiberHooks.new.js
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Original file line number Diff line number Diff line change
Expand Up @@ -914,7 +914,16 @@ function readFromUnsubcribedMutableSource<Source, Snapshot>(
}

if (isSafeToReadFromSource) {
return getSnapshot(source._source);
const snapshot = getSnapshot(source._source);
if (__DEV__) {
if (typeof snapshot === 'function') {
console.error(
'Mutable source should not return a function as the snapshot value. ' +
'Functions may close over mutable values and cause tearing.',
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This message probably isn't great. Happy to change it.

);
}
}
return snapshot;
} else {
// This handles the special case of a mutable source being shared beween renderers.
// In that case, if the source is mutated between the first and second renderer,
Expand Down Expand Up @@ -992,6 +1001,15 @@ function useMutableSource<Source, Snapshot>(
const maybeNewVersion = getVersion(source._source);
if (!is(version, maybeNewVersion)) {
const maybeNewSnapshot = getSnapshot(source._source);
if (__DEV__) {
if (typeof maybeNewSnapshot === 'function') {
console.error(
'Mutable source should not return a function as the snapshot value. ' +
'Functions may close over mutable values and cause tearing.',
);
}
}

if (!is(snapshot, maybeNewSnapshot)) {
setSnapshot(maybeNewSnapshot);

Expand Down
20 changes: 19 additions & 1 deletion packages/react-reconciler/src/ReactFiberHooks.old.js
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Original file line number Diff line number Diff line change
Expand Up @@ -900,7 +900,16 @@ function readFromUnsubcribedMutableSource<Source, Snapshot>(
}

if (isSafeToReadFromSource) {
return getSnapshot(source._source);
const snapshot = getSnapshot(source._source);
if (__DEV__) {
if (typeof snapshot === 'function') {
console.error(
'Mutable source should not return a function as the snapshot value. ' +
'Functions may close over mutable values and cause tearing.',
);
}
}
return snapshot;
} else {
// This handles the special case of a mutable source being shared beween renderers.
// In that case, if the source is mutated between the first and second renderer,
Expand Down Expand Up @@ -978,6 +987,15 @@ function useMutableSource<Source, Snapshot>(
const maybeNewVersion = getVersion(source._source);
if (!is(version, maybeNewVersion)) {
const maybeNewSnapshot = getSnapshot(source._source);
if (__DEV__) {
if (typeof maybeNewSnapshot === 'function') {
console.error(
'Mutable source should not return a function as the snapshot value. ' +
'Functions may close over mutable values and cause tearing.',
);
}
}

if (!is(snapshot, maybeNewSnapshot)) {
setSnapshot(maybeNewSnapshot);

Expand Down
28 changes: 28 additions & 0 deletions packages/react-reconciler/src/__tests__/useMutableSource-test.internal.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1493,6 +1493,34 @@ describe('useMutableSource', () => {
},
);

// @gate experimental
it('warns about functions being used as snapshot values', async () => {
const source = createSource(() => 'a');
const mutableSource = createMutableSource(source);

const getSnapshot = () => source.value;

function Read() {
const fn = useMutableSource(mutableSource, getSnapshot, defaultSubscribe);
const value = fn();
Scheduler.unstable_yieldValue(value);
return value;
}

const root = ReactNoop.createRoot();
await act(async () => {
root.render(
<>
<Read />
</>,
);
expect(() => expect(Scheduler).toFlushAndYield(['a'])).toErrorDev(
'Mutable source should not return a function as the snapshot value.',
);
});
expect(root).toMatchRenderedOutput('a');
});

// @gate experimental
it('getSnapshot changes and then source is mutated during interleaved event', async () => {
const {useEffect} = React;
Expand Down