Replaced post-processing "use client" build step with Parcel plug-in

.parcelrc

@@ -0,0 +1,6 @@
+{
+  "extends": "@parcel/config-default",
+  "optimizers": {
+    "*.{js,mjs,cjs}": ["./parcel-optimizer-use-client.js"]
+  }
+}

package.json

@@ -21,7 +21,7 @@
     "clear:builds": "rm -rf ./dist",
     "clear:parcel-cache": "rm -rf ./.parcel-cache",
     "clear:node_modules": "rm -rf ./node_modules",
-    "prerelease": "rm -rf ./.parcel-cache && parcel build && ./postprocess.js",
+    "prerelease": "rm -rf ./.parcel-cache && parcel build",
     "prettier": "prettier --write \"**/*.{css,html,js,json,jsx,ts,tsx}\"",
     "prettier:ci": "prettier --check \"**/*.{css,html,js,json,jsx,ts,tsx}\"",
     "test": "jest",
@@ -33,9 +33,13 @@
     "@babel/runtime": "^7.12.5"
   },
   "devDependencies": {
+    "@parcel/config-default": "^2.9.0",
     "@parcel/core": "^2.9.0",
     "@parcel/packager-ts": "^2.9.0",
+    "@parcel/plugin": "^2.9.0",
+    "@parcel/source-map": "^2.1.1",
     "@parcel/transformer-typescript-types": "^2.9.0",
+    "@parcel/utils": "^2.9.0",
     "@types/jest": "^26.0.15",
     "@types/react": "^18",
     "@types/react-dom": "^18",

parcel-optimizer-use-client.js

@@ -0,0 +1,17 @@
+const { Optimizer } = require("@parcel/plugin");
+const { default: SourceMap } = require("@parcel/source-map/dist/node.js");
+const { blobToBuffer } = require("@parcel/utils");
+
+module.exports = new Optimizer({
+  async optimize({ contents, map, options }) {
+    let correctMap;
+    if (map != null) {
+      correctMap = new SourceMap(options.projectRoot);
+      correctMap.addSourceMap(map, 2); // Offset lines by 2
+    }
+    return {
+      contents: `"use client";\n\n` + (await blobToBuffer(contents)).toString(),
+      map: correctMap,
+    };
+  },
+});