Improvement: Add a log when react-dom is running on RSC instead of SSR

[arjunsohal12]

Addresses issue #27478, providing a better error message when react-dom is running on RSC instead of SSR by checking when ReactCurrentCache is undefined and throwing a more descriptive error.

Code changes:

  if (enableCache) {
    if (ReactCurrentCache === undefined) {
        throw new Error(
            'The "react" package in this environment is not configured correctly. The "react-server" condition must be enabled in any environment that runs React Server Components.',
        );
    }
    prevCacheDispatcher = ReactCurrentCache.current;
    ReactCurrentCache.current = DefaultCacheDispatcher;
};

What did you do to test it:

Reproduced the issue, checked if the correct error message was shown.

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[react-sizebot]

Comparing: 8c85b02...45aa5c0

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	174.94 kB	174.94 kB	=	54.44 kB	54.44 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	177.06 kB	177.06 kB	=	55.12 kB	55.12 kB
facebook-www/ReactDOM-prod.classic.js	=	567.28 kB	567.28 kB	=	99.85 kB	99.85 kB
facebook-www/ReactDOM-prod.modern.js	=	551.14 kB	551.14 kB	=	96.94 kB	96.94 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable-semver/react-server/cjs/react-server.production.min.js	+0.57%	34.67 kB	34.87 kB	+0.83%	10.98 kB	11.08 kB
oss-stable/react-server/cjs/react-server.production.min.js	+0.57%	34.67 kB	34.87 kB	+0.83%	10.98 kB	11.08 kB
oss-experimental/react-server/cjs/react-server.production.min.js	+0.53%	37.42 kB	37.62 kB	+0.75%	11.69 kB	11.78 kB
oss-stable-semver/react-dom/cjs/react-dom-server.bun.production.min.js	+0.26%	75.60 kB	75.80 kB	+0.39%	23.00 kB	23.09 kB
oss-stable/react-dom/cjs/react-dom-server.bun.production.min.js	+0.26%	75.63 kB	75.83 kB	+0.38%	23.02 kB	23.11 kB
oss-stable-semver/react-dom/cjs/react-dom-server.node.production.min.js	+0.26%	77.04 kB	77.24 kB	+0.44%	23.85 kB	23.95 kB
oss-stable/react-dom/cjs/react-dom-server.node.production.min.js	+0.26%	77.06 kB	77.26 kB	+0.44%	23.87 kB	23.98 kB
oss-stable-semver/react-dom/cjs/react-dom-server-legacy.node.production.min.js	+0.26%	77.48 kB	77.68 kB	+0.38%	23.76 kB	23.85 kB
oss-stable/react-dom/cjs/react-dom-server-legacy.node.production.min.js	+0.26%	77.51 kB	77.71 kB	+0.37%	23.78 kB	23.87 kB
oss-experimental/react-dom/cjs/react-dom-server.bun.production.min.js	+0.25%	78.50 kB	78.70 kB	+0.39%	23.78 kB	23.88 kB
oss-stable-semver/react-dom/cjs/react-dom-server.edge.production.min.js	+0.25%	78.96 kB	79.15 kB	+0.46%	24.72 kB	24.84 kB
oss-stable/react-dom/cjs/react-dom-server.edge.production.min.js	+0.25%	78.98 kB	79.18 kB	+0.46%	24.75 kB	24.86 kB
oss-experimental/react-dom/cjs/react-dom-server-legacy.node.production.min.js	+0.25%	80.34 kB	80.54 kB	+0.40%	24.54 kB	24.63 kB
oss-experimental/react-dom/cjs/react-dom-server.node.production.min.js	+0.24%	82.75 kB	82.95 kB	+0.40%	25.22 kB	25.32 kB
oss-experimental/react-dom/cjs/react-dom-server.edge.production.min.js	+0.23%	84.52 kB	84.72 kB	+0.34%	25.99 kB	26.08 kB

Generated by 🚫 dangerJS against 45aa5c0

[gaearon]

It would be nice to have a better error, but this specific place seems too specific and mostly accidental. It might crash somewhere else later. Maybe react-dom could just have a react-server conditions entry point that logs a good message? Not sure if it's meant to be unsupported completely or just warn.

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[github-actions]

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