[CS2] Don’t require async/await support to run coffee (#4679)

* Get `coffee` command working again in Node 6, by converting the ‘await’ wrapper in the REPL to use a Promise instead of the ‘await’ keyword; add tests for REPL ‘await’ wrapper, including test to skip async tests if the runtime doesn’t support them

* Code review

* Let's support Node 6+ if we can

Cakefile

@@ -409,6 +409,17 @@ runTests = (CoffeeScript) ->
         description: description if description?
         source: fn.toString() if fn.toString?
 
+  global.supportsAsync = if global.testingBrowser
+    try
+      new Function('async () => {}')()
+      yes
+    catch
+      no
+  else
+    [major, minor, build] = process.versions.node.split('.').map (version) ->
+      parseInt version, 10
+    major >= 8 or (major is 7 and minor >= 6)
+
   helpers.extend global, require './test/support/helpers'
 
   # When all the tests have run, collect and print errors.
@@ -428,6 +439,8 @@ runTests = (CoffeeScript) ->
 
   # Run every test in the `test` folder, recording failures.
   files = fs.readdirSync 'test'
+  unless global.supportsAsync # Except for async tests, if async isn’t supported.
+    files = files.filter (filename) -> filename isnt 'async.coffee'
 
   for file in files when helpers.isCoffee file
     literate = helpers.isLiterate file

package.json

@@ -11,7 +11,7 @@
   "version": "2.0.0-beta4",
   "license": "MIT",
   "engines": {
-    "node": ">=7.6.0"
+    "node": ">=6"
   },
   "directories": {
     "lib": "./lib/coffeescript"

src/repl.coffee

@@ -44,9 +44,9 @@ replDefaults =
       result = runInContext js, context, filename
       # Await an async result, if necessary
       if isAsync
-        result = await result
-        cb null, result unless sawSIGINT
-        sawSIGINT = false
+        result.then (resolvedResult) ->
+          cb null, resolvedResult unless sawSIGINT
+        sawSIGINT = no
       else
         cb null, result
     catch err

test/repl.coffee

@@ -115,6 +115,13 @@ testRepl "keeps running after runtime error", (input, output) ->
   input.emitLine 'a'
   eq 'undefined', output.lastWrite()
 
+testRepl "#4604: wraps an async function", (input, output) ->
+  return unless global.supportsAsync
+  input.emitLine 'await new Promise (resolve) -> setTimeout (-> resolve 33), 10'
+  setTimeout ->
+    eq '33', output.lastWrite()
+  , 20
+
 process.on 'exit', ->
   try
     fs.unlinkSync historyFile