lens/tsconfig.extensions.json

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "module": "CommonJS",
    "declaration": true, // should output .d.ts
    "sourceMap": true, // for use with webpack's devtool: 'inline-source-map'
    "outDir": "./src/extensions/npm/extensions/dist" // where .d.ts output
  }
}