Fix ARM detection on armv7l Node

Several versions of Node for armv7l incorrectly identify as
`arm_version: '6'`.

See: nodejs/node#4531 and related

package.json

@@ -49,6 +49,7 @@
     "eslint-plugin-standard": "^3.0.0",
     "nyc": "^11.0.0",
     "pkg-up": "^2.0.0",
+    "sinon": "^4.1.3",
     "tempy": "^0.2.1",
     "which": "^1.2.14"
   },

targets.js

@@ -1,5 +1,6 @@
 'use strict'
 
+const execSync = require('child_process').execSync
 const semver = require('semver')
 
 const officialArchs = ['ia32', 'x64', 'armv7l', 'arm64']
@@ -73,9 +74,16 @@ function warnIfAllNotSpecified (opts, message) {
 }
 
 function hostArch () {
-  /* istanbul ignore if */
-  if (process.arch === 'arm' && process.config.variables.arm_version === '7') {
-    return 'armv7l'
+  if (process.arch === 'arm') {
+    switch (process.config.variables.arm_version) {
+      case '6':
+        return module.exports.unameArch()
+      case '7':
+        return 'armv7l'
+      default:
+        const common = require('./common')
+        common.warning(`Could not determine specific ARM arch. Detected ARM version: ${JSON.stringify(process.config.variables.arm_version)}`)
+    }
   }
 
   return process.arch
@@ -97,6 +105,13 @@ module.exports = {
   officialPlatforms: officialPlatforms,
   osModules: osModules,
   supported: supported,
+  /**
+   * Returns the arch name from the `uname` utility.
+   */
+  unameArch: function unameArch () {
+    /* istanbul ignore next */
+    return execSync('uname -m').toString().trim()
+  },
   // Validates list of architectures or platforms.
   // Returns a normalized array if successful, or throws an Error.
   validateListFromOptions: function validateListFromOptions (opts, name) {

test/targets.js

@@ -1,6 +1,7 @@
 'use strict'
 
 const config = require('./config.json')
+const sinon = require('sinon')
 const targets = require('../targets')
 const test = require('ava')
 const util = require('./_util')
@@ -51,6 +52,17 @@ test('validateListFromOptions does not take non-Array/String values', t => {
   delete targets.supported.digits
 })
 
+test('validateListFromOptions works for armv7l host and target arch', t => {
+  const sandbox = sinon.createSandbox()
+
+  sandbox.stub(process, 'arch').value('arm')
+  sandbox.stub(process, 'config').value({variables: {arm_version: '7'}})
+
+  t.deepEqual(targets.validateListFromOptions({}, 'arch'), ['armv7l'])
+
+  sandbox.restore()
+})
+
 testMultiTarget('build for all available official targets', {all: true, electronVersion: '1.8.0'},
                 util.allPlatformArchCombosCount,
                 'Packages should be generated for all possible platforms')
@@ -76,6 +88,40 @@ test('fails with invalid platform', util.invalidOptionTest({
   platform: 'dos'
 }))
 
+test('hostArch detects incorrectly configured armv7l Node', t => {
+  const sandbox = sinon.createSandbox()
+
+  sandbox.stub(targets, 'unameArch').returns('armv7l')
+  sandbox.stub(process, 'arch').value('arm')
+  sandbox.stub(process, 'config').value({variables: {arm_version: '6'}})
+
+  t.is(targets.hostArch(), 'armv7l')
+
+  sandbox.restore()
+})
+
+test('hostArch detects correctly configured armv7l Node', t => {
+  const sandbox = sinon.createSandbox()
+
+  sandbox.stub(process, 'arch').value('arm')
+  sandbox.stub(process, 'config').value({variables: {arm_version: '7'}})
+
+  t.is(targets.hostArch(), 'armv7l')
+
+  sandbox.restore()
+})
+
+test('hostArch cannot determine ARM version', t => {
+  const sandbox = sinon.createSandbox()
+
+  sandbox.stub(process, 'arch').value('arm')
+  sandbox.stub(process, 'config').value({variables: {arm_version: '99'}})
+
+  t.is(targets.hostArch(), 'arm')
+
+  sandbox.restore()
+})
+
 testMultiTarget('invalid official combination', {arch: 'ia32', platform: 'darwin'}, 0, 'Package should not be generated for invalid official combination')
 testMultiTarget('platform=linux and arch=arm64 with a supported official Electron version', {arch: 'arm64', platform: 'linux', electronVersion: '1.8.0'}, 1, 'Package should be generated for arm64')
 testMultiTarget('platform=linux and arch=arm64 with an unsupported official Electron version', {arch: 'arm64', platform: 'linux'}, 0, 'Package should not be generated for arm64')