Merge pull request #10708 from atom/flow-implies-babel

Flow implies Babel

build/lib/uses-babel.coffee

@@ -4,6 +4,7 @@ BABEL_PREFIXES = [
   "'use babel'"
   '"use babel"'
   '/** @babel */'
+  '/* @flow */'
 ]
 
 PREFIX_LENGTH = Math.max(BABEL_PREFIXES.map((prefix) -> prefix.length)...)

spec/babel-spec.coffee

@@ -36,6 +36,11 @@ describe "Babel transpiler support", ->
       transpiled = require('./fixtures/babel/babel-double-quotes.js')
       expect(transpiled(3)).toBe 4
 
+  describe 'when a .js file starts with /* @flow */', ->
+    it "transpiles it using babel", ->
+      transpiled = require('./fixtures/babel/flow-comment.js')
+      expect(transpiled(3)).toBe 4
+
   describe "when a .js file does not start with 'use babel';", ->
     it "does not transpile it using babel", ->
       expect(-> require('./fixtures/babel/invalid.js')).toThrow()

spec/fixtures/babel/flow-comment.js

@@ -0,0 +1,4 @@
+/* @flow */
+
+const f: Function = v => v + 1
+module.exports = f

src/babel.js

@@ -10,7 +10,8 @@ var babelVersionDirectory = null
 var PREFIXES = [
   '/** @babel */',
   '"use babel"',
-  '\'use babel\''
+  '\'use babel\'',
+  '/* @flow */'
 ]
 
 var PREFIX_LENGTH = Math.max.apply(Math, PREFIXES.map(function (prefix) {