feature request: inject special env vars/runtime vars to detect `--local` mode

With miniflare one could inject an environment variable in build scripts to delineate slightly differently between a real worker and one that runs locally.

see

https://github.com/cloudflare/miniflare/blob/5d9032470247173c54f4fecfc4f7750f10beaee8/packages/core/src/plugins/build.ts#L73

This is helpful to get around the lack of support of secrets so could be used like;

// file: my-app.js

const get_jwt_factory = (secret) =>
   HS256({
     key: secret,
     expires: 86400, // 24 hours
   });

export const jwt = (env) => get_jwt_factory(__DEV__ ? 'test-key' : env.JWT_SECRET);

// file: worktop.config.js

import { define } from 'worktop.build';

export default define({
	modify(config) {
		config.define = {
			__DEV__: JSON.stringify(process.env.MINIFLARE === '1'),
		};
	},
});

would be nice to bring this environment variable back.

[threepointone]

We landed initial support for dotenv style injection in https://github.com/cloudflare/wrangler2/pull/879 tldr make a file called .dev.vars in your project root

[threepointone]

I think a better solution would be to use environments. In your wrangler.toml, you can set up

[vars]
secret = 'actual-key'

[build]
command = "npm run build"

[env.dev.vars]
secret = 'test-key'

[env.dev.build]
command = "DEV=1 npm run build"

So you can run wrangler dev --env dev and it’ll load test-key.

To be clear, this tackles multiple separate issues -

• injecting variables into a build time process, which you can with regular system environment variables. We also landed dotenv support, so you can use .env files as well.
• injecting runtime vars, which you can do with wrangler.toml/--env/[vars]
• additionally, if you want to inject variables only during wrangler dev you can use dev.vars, which uses dotenv syntax.

I don’t think we have any plans right now to introduce any variables to detect whether we’re running local vs remote modes, but I’ll leave this issue open till we actually discuss and decide. This is also not a regression since we never supported it, and I’ve amended the title to reflect that.