Initial Flow support

.babelrc

@@ -1,4 +1,10 @@
 {
-  "presets": ['react', 'es2015', 'stage-0'],
-  "plugins": []
+  "presets": [
+    'react',
+    'es2015',
+    'stage-0'
+  ],
+  "plugins": [
+    'transform-flow-strip-types'
+  ]
 }

.eslintignore

@@ -0,0 +1 @@
+interfaces

.eslintrc

@@ -5,7 +5,9 @@
     "plugin:ava/recommended"
   ],
   "plugins": [
-    "ava"
+    "ava",
+    "flowtype",
+    "flow-vars"
   ],
   "rules": {
     "indent": [2, 2, {"SwitchCase": 1}],
@@ -20,9 +22,37 @@
     "react/prefer-stateless-function": [0],
     "no-underscore-dangle": ["error", { "allow": ["_config"] }],
     "import/no-unresolved": [0],
-    "global-require": [0]
+    "global-require": [0],
+    "no-duplicate-imports": [0],
+    "flowtype/require-parameter-type": 1,
+    "flowtype/require-return-type": [
+      1,
+      "always",
+      {
+        "annotateUndefined": "never"
+      }
+    ],
+    "flowtype/space-after-type-colon": [
+      1,
+      "always"
+    ],
+    "flowtype/space-before-type-colon": [
+      1,
+      "never"
+    ],
+    "flowtype/type-id-match": [
+      0,
+      "^([A-Z][a-z0-9]+)+Type$"
+    ],
+    "flow-vars/define-flow-type": 1,
+    "flow-vars/use-flow-type": 1,
   },
   "globals": {
     "__PREFIX_LINKS__": true,
   },
+  "settings": {
+    "flowtype": {
+      "onlyFilesWithFlowAnnotation": true
+    }
+  }
 }

.flowconfig

@@ -0,0 +1,24 @@
+[version]
+0.27.0
+
+[ignore]
+.*/node_modules/.*
+.*/test/.*
+
+[include]
+node_modules
+
+[libs]
+./interfaces/
+node_modules/iflow-debug/index.js.flow
+node_modules/iflow-lodash/index.js.flow
+node_modules/iflow-react-router/index.js.flow
+
+[options]
+esproposal.class_instance_fields=enable
+esproposal.class_static_fields=enable
+
+strip_root=true
+
+suppress_comment= \\(.\\|\n\\)*\\$FlowFixMe
+suppress_comment= \\(.\\|\n\\)*\\$FlowIssue

CONTRIBUTING.md

@@ -17,6 +17,10 @@ simple steps:
 
 Test suite can be run via `npm test`.
 
+This project uses [FlowType](https://flowtype.org/) for static type checking.
+
+**Note for Windows Users** - Flow is not currently supported on Windows. Please do not let this prevent you from contributing. If you can use a VM for this part, great! Otherwise, feel free to open a PR and ask for assistance.
+
 The usual contributing steps are:
 
 * Fork the [official repository](https://github.com/gatsbyjs/gatsby).

interfaces/front-matter.js

@@ -0,0 +1,3 @@
+declare module 'front-matter' {
+  declare var exports: (input: string) => { attributes: {}, body: string };
+}

interfaces/html-frontmatter.js

@@ -0,0 +1,3 @@
+declare module 'html-frontmatter' {
+  declare var exports: (input: string) => {};
+}

interfaces/invariant.js

@@ -0,0 +1,3 @@
+declare module 'invariant' {
+  declare var exports: (condition: any, message: string) => ?Error
+}

interfaces/object-assign.js

@@ -0,0 +1,3 @@
+declare module 'object-assign' {
+  declare var exports: (target: Object, ...sources?: Array<Object>) => {};
+}

interfaces/parse-filepath.js

@@ -0,0 +1,24 @@
+declare module 'parse-filepath' {
+  declare type FileData = {
+    root: string,
+    dir: string,
+    base: string,
+    ext: string,
+    name: string,
+
+    // aliases
+    extname: string,
+    basename: string,
+    dirname: string,
+    stem: string,
+
+    // original path
+    path: string,
+
+    // getters
+    absolute: () => string,
+    isAbsolute: () => Boolean
+  }
+
+  declare var exports: (input: string) => FileData
+}

interfaces/slash.js

@@ -0,0 +1,3 @@
+declare module 'slash' {
+  declare var exports: (input: string) => string;
+}

lib/isomorphic/create-routes.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import filter from 'lodash/filter'
 import sortBy from 'lodash/sortBy'
 import last from 'lodash/last'
@@ -96,6 +97,7 @@ module.exports = (files, pagesReq) => {
   const wrappers = {}
   staticFileTypes.forEach((type) => {
     try {
+      // $FlowIssue - https://github.com/facebook/flow/issues/1975
       wrappers[type] = require(`wrappers/${type}`)
     } catch (e) {
       // Ignore error.

lib/isomorphic/gatsby-helpers.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import { config } from 'config'
 import invariant from 'invariant'
 import isString from 'lodash/isString'

lib/isomorphic/html.js

@@ -1,3 +1,5 @@
+/* @flow weak */
+
 import React, { PropTypes } from 'react'
 import { prefixLink } from 'gatsby-helpers'
 

lib/isomorphic/pages/_template.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import React, { PropTypes } from 'react'
 
 const defaultMessage = `

lib/isomorphic/wrappers/html.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import React, { PropTypes } from 'react'
 
 module.exports = React.createClass({

lib/isomorphic/wrappers/md.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import React, { PropTypes } from 'react'
 
 module.exports = React.createClass({

lib/loaders/config-loader/index.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 const toml = require('toml')
 const loaderUtils = require('loader-utils')
 const path = require('path')

lib/loaders/html-loader/index.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import htmlFrontMatter from 'html-frontmatter'
 import objectAssign from 'object-assign'
 

lib/loaders/markdown-loader/index.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import frontMatter from 'front-matter'
 import markdownIt from 'markdown-it'
 import hljs from 'highlight.js'

lib/utils/babel-config.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import resolve from 'babel-core/lib/helpers/resolve'
 import fs from 'fs'
 import path from 'path'
@@ -104,6 +105,7 @@ function findBabelrc (directory) {
  */
 function findBabelPackage (directory) {
   try {
+    // $FlowIssue - https://github.com/facebook/flow/issues/1975
     const packageJson = require(path.join(directory, 'package.json'))
     return packageJson.babel
   } catch (error) {

lib/utils/build-css.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import webpack from 'webpack'
 import webpackConfig from './webpack.config'
 import fs from 'fs'

lib/utils/build-html.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 require('node-cjsx').transform()
 import webpack from 'webpack'
 import globPages from './glob-pages'

lib/utils/build-javascript.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import webpack from 'webpack'
 import webpackConfig from './webpack.config'
 

lib/utils/build-page/index.js

@@ -1,12 +1,13 @@
+/* @flow */
 import path from 'path'
 import objectAssign from 'object-assign'
 import pathResolver from './path-resolver'
 import loadFrontmatter from './load-frontmatter'
 
-export default function buildPage (directory, page) {
+export default function buildPage (directory: string, page: string) {
   const pageData = loadFrontmatter(page)
 
-  const relativePath = path.relative(path.join(directory, 'pages'), page)
+  const relativePath: string = path.relative(path.join(directory, 'pages'), page)
   const pathData = pathResolver(relativePath, pageData)
 
   return objectAssign({}, pathData, { data: pageData })

lib/utils/build-page/load-frontmatter.js

@@ -1,11 +1,12 @@
+/* @flow */
 import fs from 'fs'
 import path from 'path'
 import frontMatter from 'front-matter'
 import objectAssign from 'object-assign'
 import htmlFrontMatter from 'html-frontmatter'
 
-export default function loadFrontmatter (pagePath) {
-  const ext = path.extname(pagePath).slice(1)
+export default function loadFrontmatter (pagePath: string): {} {
+  const ext: string = path.extname(pagePath).slice(1)
 
   // Load data for each file type.
   // TODO use webpack-require to ensure data loaded
@@ -14,10 +15,11 @@ export default function loadFrontmatter (pagePath) {
 
   let data
   if (ext === 'md') {
-    const rawData = frontMatter(fs.readFileSync(pagePath, 'utf-8'))
+    const rawData = frontMatter(fs.readFileSync(pagePath, { encoding: 'utf-8' }))
     data = objectAssign({}, rawData.attributes)
   } else if (ext === 'html') {
-    const html = fs.readFileSync(pagePath, 'utf-8')
+    const html = fs.readFileSync(pagePath, { encoding: 'utf-8' })
+    // $FlowIssue - https://github.com/facebook/flow/issues/1870
     data = objectAssign({}, htmlFrontMatter(html), { body: html })
   } else {
     data = {}

lib/utils/build-page/path-resolver.js

@@ -1,8 +1,10 @@
+/* @flow */
 import slash from 'slash'
 import parsePath from 'parse-filepath'
 import urlResolver from './url-resolver'
 
-export default function pathResolver (relativePath, pageData={}) {
+
+export default function pathResolver (relativePath: string, pageData: {} = {}) {
   const data = {}
 
   data.file = parsePath(relativePath)
@@ -26,3 +28,4 @@ export default function pathResolver (relativePath, pageData={}) {
 
   return data
 }
+

lib/utils/build-page/url-resolver.js

@@ -1,10 +1,12 @@
+/* @flow weak */
 import { posix as path } from 'path'
 import _, { startsWith } from 'lodash'
 import invariant from 'invariant'
 
 let rewritePath
 try {
   const gatsbyNodeConfig = path.resolve(process.cwd(), './gatsby-node')
+  // $FlowIssue - https://github.com/facebook/flow/issues/1975
   const nodeConfig = require(gatsbyNodeConfig)
   rewritePath = nodeConfig.rewritePath
 } catch (e) {

lib/utils/build.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import toml from 'toml'
 import fs from 'fs'
 import _ from 'lodash'
@@ -12,6 +13,7 @@ function customPost (program, callback) {
   const directory = program.directory
   let customPostBuild
   try {
+    // $FlowIssue - https://github.com/facebook/flow/issues/1975
     const gatsbyNodeConfig = require(`${directory}/gatsby-node`)
     customPostBuild = gatsbyNodeConfig.postBuild
   } catch (e) {

lib/utils/develop.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 require('node-cjsx').transform()
 import Hapi from 'hapi'
 import Boom from 'boom'

lib/utils/glob-pages.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import glob from 'glob'
 import buildPage from './build-page'
 const debug = require('debug')('gatsby:glob')

lib/utils/init-starter.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import { exec } from 'child_process'
 import fs from 'fs-extra'
 import sysPath from 'path'

lib/utils/load-context.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 // This file is auto-written and used by Gatsby to require
 // files from your pages directory.
 module.exports = function (callback) {

lib/utils/new.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 const logger = require('tracer').colorConsole()
 
 const initStarter = require('./init-starter')

lib/utils/post-build.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import path from 'path'
 import glob from 'glob'
 import fs from 'fs-extra'

lib/utils/serve-build.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import Hapi from 'hapi'
 import opn from 'opn'
 

lib/utils/static-entry.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import React from 'react'
 import { renderToString, renderToStaticMarkup } from 'react-dom/server'
 import { match, RouterContext } from 'react-router'

lib/utils/web-entry.js

@@ -1,3 +1,4 @@
+/* @flow weak */
 import React from 'react'
 import ReactDOM from 'react-dom'
 import { applyRouterMiddleware, browserHistory, Router } from 'react-router'

package.json

@@ -86,15 +86,22 @@
     "ava-http": "^0.2.1",
     "babel-cli": "^6.9.0",
     "babel-eslint": "^6.0.2",
+    "babel-plugin-transform-flow-strip-types": "^6.8.0",
     "babel-register": "^6.9.0",
     "bluebird": "^3.4.0",
     "cheerio": "^0.20.0",
     "eslint": "^2.11.1",
     "eslint-config-airbnb": "^9.0.1",
     "eslint-plugin-ava": "^2.5.0",
+    "eslint-plugin-flow-vars": "^0.4.0",
+    "eslint-plugin-flowtype": "^2.2.7",
     "eslint-plugin-import": "^1.8.1",
     "eslint-plugin-jsx-a11y": "^1.5.3",
     "eslint-plugin-react": "^5.1.1",
+    "flow-bin": "^0.27.0",
+    "iflow-debug": "^1.0.15",
+    "iflow-lodash": "^1.1.15",
+    "iflow-react-router": "^1.1.15",
     "nyc": "^6.6.1"
   },
   "engines": {
@@ -119,7 +126,8 @@
   "scripts": {
     "build": "babel lib --out-dir dist/",
     "lint": "eslint --ext .js,.jsx --ignore-path .gitignore .",
-    "test": "npm run lint && npm run test-node && npm run test-integration",
+    "lint:flow": "babel-node scripts/flow-check.js",
+    "test": "npm run lint && npm run test-node && npm run test-integration && npm run lint:flow",
     "test-coverage": "node_modules/.bin/nyc --reporter=lcov --reporter=text npm test",
     "test-integration": "node_modules/.bin/ava test/integration",
     "test-node": "node_modules/.bin/ava test/utils",