Compile-time variables & dead code elimination

[airjp73]

It would be really nice to be able to define variables at compile-time in remix.config.js and have dead code to be removed based on that. This would be especially useful for using the in-source testing in vitest where you would want to define import.meta.vitest to be undefined in order to eliminate dead code.

It looks like the esbuild configuration option to define variables is already being used as part of the remix compiler.

remix/packages/remix-dev/compiler.ts

Lines 388 to 393 in a2e1449

	define: {
	"process.env.NODE_ENV": JSON.stringify(options.mode),
	"process.env.REMIX_DEV_SERVER_WS_PORT": JSON.stringify(
	config.devServerPort
	),
	},

Though I'm not sure how much dead code elimination esbuild will actually do. It says here that it won't eliminate dead code within a function body, so it might only work for top-level code.

Also worth noting: I don't think exposing an option to do this would lock remix into its current compiler setup. Many other bundlers support this option. The vitest docs provide a few examples here.