feat: add Flow type checking

Add `flow check` to check for type errors as additional
linting step.

The `.flowconfig` file in the root of AEgir is needed as else
the linting would fail (although AEgir doesn't define any Flow
types). This is intentional as this branch should only be used
with projects using Flow. There this error message is really
helpful.

.flowconfig

@@ -0,0 +1,9 @@
+[ignore]
+.*/node_modules/documentation/*
+
+[libs]
+
+[include]
+
+[options]
+suppress_comment= \\(.\\|\n\\)*\\@FlowIgnore

package.json

@@ -48,6 +48,7 @@
     "execa": "^0.8.0",
     "filesize": "^3.5.11",
     "findup-sync": "^2.0.0",
+    "flow-bin": "^0.71.0",
     "fs-extra": "^4.0.3",
     "gh-pages": "^1.1.0",
     "glob": "^7.1.2",

src/lint.js

@@ -1,6 +1,10 @@
 'use strict'
 
+const util = require('util')
+const execFile = util.promisify(require('child_process').execFile)
+
 const CLIEngine = require('eslint').CLIEngine
+const flow = require('flow-bin')
 const path = require('path')
 const formatter = CLIEngine.getFormatter()
 
@@ -18,7 +22,7 @@ const FILES = [
   '!**/node_modules/**'
 ]
 
-function lint (opts) {
+const eslint = (opts) => {
   return new Promise((resolve, reject) => {
     const cli = new CLIEngine({
       useEslintrc: true,
@@ -37,4 +41,20 @@ function lint (opts) {
   })
 }
 
+const typecheck = async (_opts) => {
+  try {
+    const { stdout } = await execFile(flow, ['check', '--color=always'])
+    console.log(stdout)
+  } catch (err) {
+    console.error(err.stdout)
+    console.error(err.stderr)
+    throw new Error('Type check errors')
+  }
+}
+
+const lint = async (opts) => {
+  await eslint(opts)
+  await typecheck(opts)
+}
+
 module.exports = lint

test/lint.spec.js

@@ -6,7 +6,7 @@ const lint = require('../src/lint')
 describe('lint', () => {
   it('passes', function () {
     // slow ci is slow, appveyor is even slower...
-    this.timeout(5000)
+    this.timeout(20000)
     return lint({
       fix: false
     })