README.md

git clone https://gist.github.com/panva/a350238b643aef7a77b29e6db395c3b9 response-type-reproduction
cd response-type-reproduction
npm i
npx tsc

index.ts:4:3 - error TS2322: Type 'Promise<import("./node_modules/undici/types/fetch").Response>' is not assignable to type 'Promise<Response>'.
  Type 'import("./node_modules/undici/types/fetch").Response' is not assignable to type 'Response'.
    The types returned by 'headers.entries()' are incompatible between these types.
      Type 'SpecIterableIterator<[string, string]>' is missing the following properties from type 'HeadersIterator<[string, string]>': map, filter, take, drop, and 9 more.

4   return undici.fetch(url)
    ~~~~~~


Found 1 error in index.ts:4

index.ts

import * as undici from 'undici'

function req(url: string): Promise<Response> {
  return undici.fetch(url)
}

await req('https://nodejs.org/')

package-lock.json

{
  "name": "pg",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "pg",
      "version": "1.0.0",
      "license": "ISC",
      "dependencies": {
        "undici": "^6.19.8"
      },
      "devDependencies": {
        "@types/node": "^22.5.5",
        "typescript": "~5.6.2"
      }
    },
    "node_modules/@types/node": {
      "version": "22.5.5",
      "resolved": "https://registry.npmjs.org/@types/node/-/node-22.5.5.tgz",
      "integrity": "sha512-Xjs4y5UPO/CLdzpgR6GirZJx36yScjh73+2NlLlkFRSoQN8B0DpfXPdZGnvVmLRLOsqDpOfTNv7D9trgGhmOIA==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
        "undici-types": "~6.19.2"
      }
    },
    "node_modules/typescript": {
      "version": "5.6.2",
      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.6.2.tgz",
      "integrity": "sha512-NW8ByodCSNCwZeghjN3o+JX5OFH0Ojg6sadjEKY4huZ52TqbJTJnDo5+Tw98lSy63NZvi4n+ez5m2u5d4PkZyw==",
      "dev": true,
      "license": "Apache-2.0",
      "bin": {
        "tsc": "bin/tsc",
        "tsserver": "bin/tsserver"
      },
      "engines": {
        "node": ">=14.17"
      }
    },
    "node_modules/undici": {
      "version": "6.19.8",
      "resolved": "https://registry.npmjs.org/undici/-/undici-6.19.8.tgz",
      "integrity": "sha512-U8uCCl2x9TK3WANvmBavymRzxbfFYG+tAu+fgx3zxQy3qdagQqBLwJVrdyO1TBfUXvfKveMKJZhpvUYoOjM+4g==",
      "license": "MIT",
      "engines": {
        "node": ">=18.17"
      }
    },
    "node_modules/undici-types": {
      "version": "6.19.8",
      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.19.8.tgz",
      "integrity": "sha512-ve2KP6f/JnbPBFyobGHuerC9g1FYGn/F8n1LWTwNxCEzd6IfqTwUQcNXgEtmmQ6DlRrC1hrSrBnCZPokRrDHjw==",
      "dev": true,
      "license": "MIT"
    }
  }
}

package.json

{
  "name": "pg",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "type": "module",
  "author": "",
  "license": "ISC",
  "description": "",
  "devDependencies": {
    "@types/node": "^22.5.5",
    "typescript": "~5.6.2"
  },
  "dependencies": {
    "undici": "^6.19.8"
  }
}

tsconfig.json

{
  "include": ["**/*.ts"],
  "compilerOptions": {
    "target": "ESNext",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "types": ["node"]
  }
}