feat(config): add support for loading configs from npm itself

Author: zkat

lib/config.js

@@ -1,17 +1,56 @@
 'use strict'
 
 const figgyPudding = require('figgy-pudding')
+const spawn = require('child_process').spawn
 
-module.exports = figgyPudding({
+const frogConfig = module.exports = figgyPudding({
   also: {},
   cache: {},
   dev: {},
   development: {},
   force: {},
+  global: {},
   'ignore-scripts': {},
   log: {},
+  loglevel: {},
   only: {},
   prefix: {},
   production: {},
+  then: {}, // omfg
   umask: {}
 })
+
+module.exports.fromNpm = getNpmConfig
+async function getNpmConfig (argv) {
+  const npmBin = process.platform === 'win32' ? 'npm.cmd' : 'npm'
+  const child = spawn(npmBin, [
+    'config', 'ls', '--json', '-l'
+    // We add argv here to get npm to parse those options for us :D
+  ].concat(argv || []), {
+    env: process.env,
+    cwd: process.cwd(),
+    stdio: [0, 'pipe', 2]
+  })
+
+  let stdout = ''
+  if (child.stdout) {
+    child.stdout.on('data', (chunk) => {
+      stdout += chunk
+    })
+  }
+
+  return await new Promise((resolve, reject) => {
+    child.on('error', reject)
+    child.on('close', (code) => {
+      if (code === 127) {
+        reject(new Error('`npm` command not found. Please ensure you have npm@5.4.0 or later installed.'))
+      } else {
+        try {
+          resolve(frogConfig(JSON.parse(stdout)))
+        } catch (e) {
+          reject(new Error('`npm config ls --json` failed to output json. Please ensure you have npm@5.4.0 or later installed.'))
+        }
+      }
+    })
+  })
+}