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microsoft / react-native-windows

A framework for building native Windows apps with React.
https://microsoft.github.io/react-native-windows/
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Add RnwNewArch property and RNW_NEW_ARCH constants when building projects for the new architecture #14042

Closed jonthysell closed 2 weeks ago

jonthysell commented 3 weeks ago

Description

This PR adds a RnwNewArch MSBuild property and RNW_NEW_ARCH build-time constant / pre-processor directive for use by external (module) devs. This PR also updates @react-native-windows/codegen to use the directive when appropriate, and also applies those changes to sample-custom-component.

The expectation is that external devs now use these new properties and directives instead of the previously exposed UseFabric, UseHermes and/or UseWinUI3 props. All logic expecting external developers to manually set those props has been removed and replaced with more robust checking that keys off RnwNewArch and throws warnings or errors if the other props aren't set correctly.

In addition, this PR adds further checks to make sure external projects load the WindowsSDK props sheet, followed by the appropriate RNW props and then the RNW targets. Failure to load these import properly would always risk putting the project in a broken state, now we at least tell people what they're missing.

Note: Old arch devs will still be able to toggle UseHermes.

Type of Change

Why

We don't want end-users to have access to conditionally build their code for the new or old architectures, without having to use/replicate the current complicated un-scoped directives we use internally.

Closes #13929

What

See above.

Screenshots

N/A

Testing

Verified the flag exists and builds for the sample-custom-component. Also verified that new projects build properly.

Changelog

Should this change be included in the release notes: yes

Add RnwNewArch property and RNW_NEW_ARCH constants when building projects for the new architecture

Microsoft Reviewers: Open in CodeFlow
Yajur-Grover commented 3 weeks ago

Once this is live, will it make the use of UseFabric in new apps/libs redundant? For all versions of RNW where this property exists, we should be using RnwNewArch instead of UseFabric where relevant e.g in community modules?

jonthysell commented 2 weeks ago

@microsoft-github-policy-service rerun