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Move modern strict to experimental #28152

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merged 3 commits into from
Feb 9, 2024
Merged

Move modern strict to experimental #28152

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f552806
Move modern strict to experimental
rickhanlonii Jan 29, 2024
a92a3ac
Turn off strict effects in legacy roots with useModernStrictMode
rickhanlonii Feb 9, 2024
4afefce
Legacy mode never double invokes effects
rickhanlonii Feb 9, 2024
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5 changes: 1 addition & 4 deletions packages/react-reconciler/src/ReactFiberWorkLoop.js
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Original file line number Diff line number Diff line change
Expand Up @@ -3792,12 +3792,9 @@ function commitDoubleInvokeEffectsInDEV(
hasPassiveEffects: boolean,
) {
if (__DEV__) {
if (useModernStrictMode) {
if (useModernStrictMode && root.tag !== LegacyRoot) {
let doubleInvokeEffects = true;

if (root.tag === LegacyRoot && !(root.current.mode & StrictLegacyMode)) {
doubleInvokeEffects = false;
}
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@sammy-SC @acdlite, I fixed this bug that turned on strict effects in Legacy Mode, which may be the reason it was hard to land internally, breaking unit tests and whatnot.

Previously, legacyCommitDoubleInvokeEffectsInDEV would be called in the legacy root too (when strict mode was on), but we wouldn't fire any effects because no fiber flags were set. When we copied over the check to this block, it forces effects to be fired, since it's not checking fiber flags (by design).

We have a test that caught this, but we didn't have any test variants that enabled useModernStrictMode:

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

Line 29 in 30e2938

it('should not double invoke effects in legacy mode', async () => {

if (
root.tag === ConcurrentRoot &&
!(root.current.mode & (StrictLegacyMode | StrictEffectsMode))
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2 changes: 1 addition & 1 deletion packages/shared/ReactFeatureFlags.js
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Expand Up @@ -147,7 +147,7 @@ export const disableJavaScriptURLs = false;
// Modern <StrictMode /> behaviour aligns more with what components
// components will encounter in production, especially when used With <Offscreen />.
// TODO: clean up legacy <StrictMode /> once tests pass WWW.
export const useModernStrictMode = false;
export const useModernStrictMode = __NEXT_MAJOR__;

// Not ready to break experimental yet.
// Remove IE and MsApp specific workarounds for innerHTML
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