fix: add environment variable to disable LWC version mismatch loglines

[nrkruk]

Details

When using LWR local dev for experience sites, every SSR request logs an LWC version mismatch error. This is due to the fact that the engine-server is intentionally reloaded on a per page basis and not cached in memory. Therefore the mechanisms in place to only log a the version mismatch once do not work. The logging noise from this makes observing actual useful errors during SSR more difficult.

My change just introduces a new environment variable that can be set on the LWR side to disable this logging during local development.

Would like to backport this also to spring25

Does this pull request introduce a breaking change?

• 😮‍💨 No, it does not introduce a breaking change.

Does this pull request introduce an observable change?

• 🤞 No, it does not introduce an observable change.

GUS work item

@W-17740011@

[divmain]

We'd need a build-time complement to this environment variable. E.g. when we compile @lwc/engine-dom, this code path should turn into if (false) { and be minified away.

[nrkruk]

@divmain not super familiar with the lwc codebase, can you point me where to make this change?

[wjhsf]

@divmain is this the right place to do it?

lwc/scripts/rollup/rollup.config.js

Lines 53 to 79 in e0437d3

	function sharedPlugins() {
	const engineBrowserConfig = ['@lwc/engine-server', '@lwc/engine-dom'].includes(packageName) && {
	// This is only used inside @lwc/engine-dom and @lwc/engine-server
	// Elsewhere, it _not_ be replaced, so that it can be replaced later (e.g. in @lwc/engine-core)
	'process.env.IS_BROWSER': packageName === '@lwc/engine-dom' ? 'true' : 'false',
	};
	return [
	typescript({
	tsconfig: path.join(packageRoot, 'tsconfig.json'),
	exclude: ['**/__tests__/**'],
	noEmitOnError: !watchMode, // in watch mode, do not exit with an error if typechecking fails
	...(watchMode && {
	incremental: true,
	outputToFilesystem: true,
	}),
	declarationDir: 'dist', // must match `output.file` in the overall Rollup config
	}),
	replace({
	values: {
	...engineBrowserConfig,
	'process.env.LWC_VERSION': JSON.stringify(version),
	},
	preventAssignment: true,
	}),
	];
	}

[divmain]

Yes, the replace plugin is correct.

[wjhsf]

Suggested change

	}).not.toLogErrorDev(
	new RegExp(
	`LWC WARNING: current engine is v${process.env.LWC_VERSION}, but template was compiled with v123.456.789`
	)
	);
	}).not.toLogErrorDev(/v123\.456\.789/);

Checking that we're not logging such a long message feels easy to get an accidental false positive, if the error text ever changes. We should just check for keywords to be more flexible.

[nrkruk]

sure I can make it more generic

[wjhsf]

process?.env
Are we expecting to encounter a scenario where the process variable is declared but null/undefined?

[nrkruk]

was just being extra cautious - I didn't know how things were compiled (and what is shipped to the browser vs whats available in server side engine). Didn't want to unintentionally break something for this one usecase.