Warn if no files field in package.json or .npmignore file present

source/npm/util.js

@@ -1,8 +1,12 @@
 'use strict';
+const {existsSync} = require('fs');
+const {resolve} = require('path');
 const execa = require('execa');
 const pTimeout = require('p-timeout');
 const ow = require('ow');
 const npmName = require('npm-name');
+const chalk = require('chalk');
+const pkgDir = require('pkg-dir');
 const {verifyRequirementSatisfied} = require('../version');
 
 exports.checkConnection = () => pTimeout(
@@ -87,3 +91,14 @@ exports.verifyRecentNpmVersion = async () => {
 	const npmVersion = await exports.version();
 	verifyRequirementSatisfied('npm', npmVersion);
 };
+
+exports.checkIgnoreStrategy = ({files}) => {
+	const rootDir = pkgDir.sync();
+	const npmignoreExists = existsSync(resolve(rootDir, '.npmignore'));
+
+	if (!files && !npmignoreExists) {
+		console.log(`
+		\n${chalk.bold.yellow('Warning:')} No ${chalk.bold.cyan('files')} field specified in ${chalk.bold.magenta('package.json')} nor ${chalk.bold.magenta('.npmignore')} file present. Setting one of those will prevent you from accidentally publishing development-specific files along with your package's source code to npm.
+		`);
+	}
+};

source/ui.js

@@ -5,7 +5,7 @@ const githubUrlFromGit = require('github-url-from-git');
 const isScoped = require('is-scoped');
 const util = require('./util');
 const git = require('./git-util');
-const {prereleaseTags} = require('./npm/util');
+const {prereleaseTags, checkIgnoreStrategy} = require('./npm/util');
 const version = require('./version');
 const prettyVersionDiff = require('./pretty-version-diff');
 
@@ -54,6 +54,8 @@ module.exports = async (options, pkg) => {
 	const extraBaseUrls = ['gitlab.com'];
 	const repoUrl = pkg.repository && githubUrlFromGit(pkg.repository.url, {extraBaseUrls});
 
+	checkIgnoreStrategy(pkg);
+
 	console.log(`\nPublish a new version of ${chalk.bold.magenta(pkg.name)} ${chalk.dim(`(current: ${oldVersion})`)}\n`);
 
 	const prompts = [