can't emit import when overwrite declare

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Even if you think you've found a *bug*, please read the FAQ first, especially the Common "Bugs" That Aren't Bugs section! Please help us by doing the following steps before logging an issue: * Search: https://github.com/Microsoft/TypeScript/search?type=Issues * Read the FAQ: https://github.com/Microsoft/TypeScript/wiki/FAQ Please fill in the *entire* template below. --> <!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.2.0-dev.201xxxxx <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** **Code** ```ts import hashSum = require('hash-sum'); import shortid = require('shortid'); declare function shortid(): string declare function hashSum(input): string export function hashAny(seed?, ...argv): string { if (!seed) { seed = shortid() } else if (typeof seed !== 'string') { seed = hashSum(seed) } return String(seed) } export default hashAny; ``` **Expected behavior:** > output js file include ```ts const hashSum = require("hash-sum"); const shortid = require("shortid"); ``` **Actual behavior:** > miss require `hash-sum`, `shortid` ```ts "use strict"; Object.defineProperty(exports, "__esModule", { value: true }); function hashAny(seed, ...argv) { if (!seed) { seed = shortid(); } else if (typeof seed !== 'string') { seed = hashSum(seed); } return String(seed); } exports.hashAny = hashAny; exports.default = hashAny; ``` **Playground Link:** <!-- A link to a TypeScript Playground "Share" link which demonstrates this behavior --> **Related Issues:** <!-- Did you find other bugs that looked similar? -->