Separate strict effects mode feature flags #20847
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rickhanlonii
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February 24, 2021 14:54
…y subtrees into strict mode level one ('mode == StrictModeL1'). This mode enables DEV-only double rendering, double component lifecycles, string ref warnings, legacy context warnings, etc. The primary purpose of this mode is to help detected render phase side effects. No new behavior. Roots created with experimental 'createRoot' and 'createBlockingRoot' APIs will also (for now) continue to default to strict mode level 1.
In a subsequent commit I will add support for a 'level' attribute on the '<React.StrictMode>' tag (as well as a new option supported by ). This will be the way to opt into strict mode level 2 ('mode == StrictModeL2'). This mode will enable DEV-only double invoking of effects on initial mount. This will simulate future Offscreen API semantics for trees being mounted, then hidden, and then shown again. The primary purpose of this mode is to enable applications to prepare for compatibility with the new Offscreen API (more information to follow shortly).
For now, this commit changes no public facing behavior. The only mechanism for opting into strict mode level 2 is the pre-existing 'enableDoubleInvokingEffects' feature flag (only enabled within Facebook for now).
StrictModeL1 -> StrictLegacyMode and StrictModeL2 -> StrictEffectsMode
One flag ('enableStrictEffects') enables strict mode level 2. It is similar to 'debugRenderPhaseSideEffectsForStrictMode' which enables srtict mode level 1.
The second flag ('createRootStrictEffectsByDefault') controls the default strict mode level for 'createRoot' trees. For now, all 'createRoot' trees remain level 1 by default. We will experiment with level 2 within Facebook.
This is a prerequisite for adding a configurable option to 'createRoot' that enables choosing a different StrictMode level than the default.
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Merged via #20849 |
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PR Stack
Builds on top of PR #20844
The feature flag that was previously
debugRenderPhaseSideEffectsForStrictModehas been split into two flags:enableStrictEffects*: This enables the new strict effects mode.createRootStrictEffectsByDefault: This determines whethercreateRoot(andcreateBlockingRoot) apps will default to strict effects mode (if true) or strict mode (if false).For now, both flags are only enabled within Facebook for testing purposes.
I've renamed strict effects test files slightly to better reflect their purpose but there were no other substantial changes.
Next step in this stack of PRs will be to add support for a new
StrictMode"level" attribute to toggle between these modes as well as a newcreateRootoption to change the default mode for the tree. This PR unblocks the latter.External changes?
For now, this commit changes no public facing behavior. The only mechanism for opting into strict mode level 2 is the
createRootStrictEffectsByDefaultfeature flag (only enabled within Facebook for now).