Add dummy legacy configs

.eslintrc.js

@@ -13,7 +13,7 @@ module.exports = {
   },
   overrides: [
     {
-      files: ["{bin,test}/**/*.js"],
+      files: ["{bin,test,scripts}/**/*.js"],
       rules: {
         "no-undef": "error",
         "no-restricted-syntax": [

scripts/build.js

@@ -41,3 +41,25 @@ for (const { src, dest = src, transform } of FILES_TO_COPY) {
     fs.copyFileSync(path.join(DIR, src), path.join(BUILD, dest));
   }
 }
+
+const LEGACY_CONFIGS = [
+  "@typescript-eslint",
+  "babel",
+  "flowtype",
+  "react",
+  "standard",
+  "unicorn",
+  "vue",
+];
+
+function legacyConfigStub(name) {
+  return `
+throw new Error(
+  '"prettier/${name}" has been merged into "prettier" in eslint-config-prettier 8.0.0. See: https://github.com/prettier/eslint-config-prettier/blob/main/CHANGELOG.md#version-800-2021-02-21'
+);
+  `.trim();
+}
+
+for (const name of LEGACY_CONFIGS) {
+  fs.writeFileSync(path.join(BUILD, `${name}.js`), legacyConfigStub(name));
+}