ethers.js/packages/bignumber/tsconfig.json

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