ethers.js/packages/experimental/tsconfig.json

{
  "compilerOptions": {
    "outDir": "./lib/",
    "rootDir": "./src.ts"
  },
  "exclude": [],
  "extends": "../../tsconfig.package.json",
  "include": [
    "./src.ts/*.ts",
    "./thirdparty.d.ts"
  ]
}