Transpile REPL (#4729)

* Fix #4725: apply transpile option to require’d .coffee files

* Use the current module’s options if it has any, before going searching up the tree

* Don’t mutate passed-in options object

* If the REPL is run with `--transpile`, turn transpilation on for both the current REPL input and any files imported by that input

* Use the command.coffee machinery for parsing arguments

* Fix test for Windows

Author: GeoffreyBooth

lib/coffeescript/command.js

@@ -92,6 +92,7 @@ exports.run = ->
   replCliOpts = useGlobal: yes
   opts.prelude = makePrelude opts.require       if opts.require
   replCliOpts.prelude = opts.prelude
+  replCliOpts.transpile = opts.transpile
   return forkNode()                             if opts.nodejs
   return usage()                                if opts.help
   return version()                              if opts.version

lib/coffeescript/repl.js

@@ -6,6 +6,7 @@ CoffeeScript = require './'
 {merge, updateSyntaxError} = require './helpers'
 
 sawSIGINT = no
+transpile = no
 
 replDefaults =
   prompt: 'coffee> ',
@@ -35,14 +36,19 @@ replDefaults =
       ast = CoffeeScript.nodes tokens
       # Add assignment to `__` variable to force the input to be an expression.
       ast = new Block [new Assign (new Value new Literal '__'), ast, '=']
-      # Wrap the expression in a closure to support top-level `await`
+      # Wrap the expression in a closure to support top-level `await`.
       ast     = new Code [], ast
       isAsync = ast.isAsync
-      # Invoke the wrapping closure
+      # Invoke the wrapping closure.
       ast    = new Block [new Call ast]
       js     = ast.compile {bare: yes, locals: Object.keys(context), referencedVars, sharedScope: yes}
+      if transpile
+        js = transpile.transpile(js, transpile.options).code
+        # Strip `"use strict"`, to avoid an exception on assigning to
+        # undeclared variable `__`.
+        js = js.replace /^"use strict"|^'use strict'/, ''
       result = runInContext js, context, filename
-      # Await an async result, if necessary
+      # Await an async result, if necessary.
       if isAsync
         result.then (resolvedResult) ->
           cb null, resolvedResult unless sawSIGINT
@@ -167,6 +173,31 @@ module.exports =
 
     CoffeeScript.register()
     process.argv = ['coffee'].concat process.argv[2..]
+    if opts.transpile
+      try
+        transpile = {}
+        transpile.transpile = require('babel-core').transform
+      catch
+        console.error '''
+          To use --transpile with an interactive REPL, babel-core must be installed either in the current folder or globally:
+            npm install --save-dev babel-core
+          or
+            npm install --global babel-core
+          And you must save options to configure Babel in one of the places it looks to find its options.
+          See http://coffeescript.org/#transpilation
+        '''
+        process.exit 1
+      transpile.options =
+        filename: path.resolve process.cwd(), '<repl>'
+      # Since the REPL compilation path is unique (in `eval` above), we need
+      # another way to get the `options` object attached to a module so that
+      # it knows later on whether it needs to be transpiled. In the case of
+      # the REPL, the only applicable option is `transpile`.
+      Module = require 'module'
+      originalModuleLoad = Module::load
+      Module::load = (filename) ->
+        @options = transpile: transpile.options
+        originalModuleLoad.call @, filename
     opts = merge replDefaults, opts
     repl = nodeREPL.start opts
     runInContext opts.prelude, repl.context, 'prelude' if opts.prelude

src/command.coffee

@@ -122,6 +122,10 @@ testRepl "#4604: wraps an async function", (input, output) ->
     eq '33', output.lastWrite()
   , 20
 
+testRepl "transpile REPL", (input, output) ->
+  input.emitLine 'require("./test/importing/transpile_import").getSep()'
+  eq "'#{path.sep.replace '\\', '\\\\'}'", output.lastWrite()
+
 process.on 'exit', ->
   try
     fs.unlinkSync historyFile