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This pull request was exported from Phabricator. Differential Revision: D57742907 |
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May 23, 2024 15:56
Summary: This diff makes the `hermes-canary` transform profile identical to `hermes-stable` by enabling destructuring. Differential Revision: D57738865
Summary: Enables regenerator for `hermes-canary`. Along with the previous diff, regenerator is the only difference between `hermes-stable` and `hermes-canary`. Differential Revision: D57742907
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This pull request was exported from Phabricator. Differential Revision: D57742907 |
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This pull request has been merged in a0237e9. |
kosmydel
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Summary: Pull Request resolved: react#44668 Enables regenerator for `hermes-canary`. Along with the previous diff, regenerator is the only difference between `hermes-stable` and `hermes-canary`. Reviewed By: motiz88 Differential Revision: D57742907 fbshipit-source-id: ca14cb50fe976744c7fa2c0b3397e81661359f15
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Summary: ## Motivation - Dev/release consistency in correctness and performance shape. - ~10% faster dev cold builds - More responsive dev apps (~2x faster promise handling) - Improved debugging support Since #52651, Hermes profiles have lowered generators (with `enableBabelRuntime: false`), `for...of`, `?.`, `??` and optional catch binding in dev builds only, because Hermes couldn't show local variables when paused on a breakpoint in a native generator. That turned out to be a Hermes bug: a breakpoint on that a `yield` line resolved to scope-less entry code before the body had even run. It was fixed in facebook/hermes@d1238c8 (hermes-v260318099.0.2), which main has used since #58397. This removes `enableRegenerator`, so Hermes-profile dev output matches release. It also fixes a dev-only divergence - loose `for-of` never calls `iterator.return()`, so breaking out of a `for...of` over a generator skipped its `finally` in dev but not release. Note that with the default `enableBabelRuntime`, generators were already native in dev, so in practice the generator change mostly affects `enableBabelRuntime: false` setups, including RN's own Jest. (There's no good reason generator was ever conditional on `enableBabelRuntime === false` - it seems to date from #44668 and probably a misunderstanding of what the `regenerator` argument to `babel/plugin-transform-runtime` did - it doesn't make that plugin transform generators, it just rewrites the helper import.) Native generator debugging still isn't perfect on .0.2 - stepping through `try`/`catch` can stop on a `catch` line that doesn't run, and breakpoints on `yield*` lines or on a `throw` after a resume don't fire. Those already affect every default config though, so there's no regression in most cases. Regenerator has its own problems, eg breakpoints often stop a line early because statements merge into its `case` blocks. Overall, native is now a better experience. Detailed comparison in https://robhogan.github.io/reports/react-native-regenerator-removal/ ## Changelog [GENERAL] [FIXED] - Babel preset: Hermes profiles no longer lower generators, `for...of`, optional chaining, nullish coalescing or optional catch binding in dev, matching release Pull Request resolved: #59303 Test Plan: Reproduced the original bug through Hermes's `CDPAgent` test harness with `Debugger.setBreakpointByUrl`. On hermes-v250829098.0.16 and v260318099.0.1, a breakpoint on a generator's last `yield` line pauses at the generator call with only the global scope, and every local evaluates to `undefined`. On v260318099.0.2 and .0.4 it pauses at the real code with all locals. AI-driven breakpoint sweep: this preset with `dev: true, enableBabelRuntime: false`, before and after this change, over 248 source lines of generator, async function, async generator, exception and loop fixtures. A breakpoint was set on every line, each pause was mapped back through the source map, and every local was evaluated. Same results with eager and lazy compilation. | Hermes | Identical | Different, equivalent | Native better | Native worse | Mixed (loop headers) | Total | | --- | --- | --- | --- | --- | --- | --- | | 250829098.0.16 | 164 | 10 | 49 | 22 | 3 | 248 | | 260318099.0.2 | 183 | 11 | 47 | 3 | 3 | 247 | | 260318099.0.4 | 184 | 11 | 47 | 3 | 3 | 248 | Reviewed By: christophpurrer Differential Revision: D126904757 Pulled By: javache fbshipit-source-id: f2d492ec6c326b9ec8b8101832c85b921836f5ce
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Summary: Enables regenerator for
hermes-canary. Along with the previous diff, regenerator is the only difference betweenhermes-stableand hermes-canary`.Differential Revision: D57742907