[0.73] Make Hermes the default JS engine #12371
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This PR backports microsoft#12321 to 0.73. This PR makes Hermes the default JS engine for RNW going forward. For now, this is still managed by setting the `<UseHermes>` MSBuild property. However, if the property is not explicitly set, the default value in `JSEngine.props` will now be `true` instead of `false`. The property will remain exposed (and now set to `true`) in project's `ExperimentalFeatures.props` files. This will be done for new projects created with the `npx react-native-windows-init` command targeting versions with this change. (Use or omission of the `--useHermes` flag will no longer be recognized at project creation time). Hermes will also be the default for projects created with the new `npx react-native init-windows` CLI command. Current users attempting to *upgrade* their existing projects with these tools will be given a warning if they were previously using the Chakra engine, and instructions to revert back to using Chakra if necessary. However, support for Chakra will be deprecated in the future, so best to migrate sooner rather than later. In addition, this PR should also enable Hermes use when consuming the official (experimental) NuGet package binaries. Finally, this PR updates our CI infrastructure to instead denote "Chakra" (rather than "Hermes") for builds and tests. - New feature (non-breaking change which adds functionality) - Breaking change (fix or feature that would cause existing functionality to not work as expected) - This change requires a documentation update Hermes is the officially supported and maintained JS engine for React Native, and as time goes on, the cost of maintain Chakra (which hasn't been updated in years) only increases. The "new" architecture includes Hermes. Resolves microsoft#11251 See above N/A Ran existing tests Should this change be included in the release notes: yes Hermes is now the default JS engine for all new projects and will eventually be the only supported JS engine.
acoates-ms
approved these changes
Nov 10, 2023
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This PR backports #12321 to 0.73.
Description
This PR makes Hermes the default JS engine for RNW going forward.
For now, this is still managed by setting the
<UseHermes>MSBuild property. However, if the property is not explicitly set, the default value inJSEngine.propswill now betrueinstead offalse.The property will remain exposed (and now set to
true) in project'sExperimentalFeatures.propsfiles. This will be done for new projects created with thenpx react-native-windows-initcommand targeting versions with this change. (Use or omission of the--useHermesflag will no longer be recognized at project creation time). Hermes will also be the default for projects created with the newnpx react-native init-windowsCLI command.Current users attempting to upgrade their existing projects with these tools will be given a warning if they were previously using the Chakra engine, and instructions to revert back to using Chakra if necessary. However, support for Chakra will be deprecated in the future, so best to migrate sooner rather than later.
In addition, this PR should also enable Hermes use when consuming the official (experimental) NuGet package binaries.
Finally, this PR updates our CI infrastructure to instead denote "Chakra" (rather than "Hermes") for builds and tests.
Type of Change
Why
Hermes is the officially supported and maintained JS engine for React Native, and as time goes on, the cost of maintain Chakra (which hasn't been updated in years) only increases. The "new" architecture includes Hermes.
Resolves #6136
Resolves #11251
What
See above
Screenshots
N/A
Testing
Ran existing tests
Changelog
Should this change be included in the release notes: yes
Hermes is now the default JS engine for all new projects and will eventually be the only supported JS engine.
Microsoft Reviewers: Open in CodeFlow