gill/packages/build-scripts/dev-flag.ts

import { readFile } from "fs/promises";
import jscodeshift from "jscodeshift";
import { Options } from "tsup";

type Loader = NonNullable<
  NonNullable<
    Awaited<
      NonNullable<
        ReturnType<Parameters<Parameters<Plugin["setup"]>[0]["onLoad"]>[1]>
      >
    >
  >["loader"]
>;
type Plugin = NonNullable<Options["esbuildPlugins"]>[number];

function replaceDev(source: string): string {
  if (/__DEV__/.test(source) !== true) {
    return source;
  }
  const j = jscodeshift.withParser("tsx");
  const root = j(source);
  root
    .find(j.Identifier, { name: "__DEV__" })
    .replaceWith(() =>
      j.binaryExpression(
        "!==",
        j.memberExpression(
          j.memberExpression(j.identifier("process"), j.identifier("env")),
          j.identifier("NODE_ENV"),
        ),
        j.stringLiteral("production"),
      ),
    );
  return root.toSource();
}

export const DevFlagPlugin: Plugin = {
  name: "dev-flag-plugin",
  setup(build) {
    build.onLoad(
      { filter: /\.(t|j)sx?$/, namespace: "file" },
      async ({ path }) => {
        const contents = await readFile(path, "utf-8");
        const ext = path.slice(path.lastIndexOf(".") + 1);
        const loader = (ext.match(/(j|t)sx?$/) ? ext : "js") as Loader;
        return {
          contents: replaceDev(contents),
          loader,
        };
      },
    );
  },
};