fixes #1724 for heregexen

TODO: DRY up that regex handling code so we don't have a duplicate test/error

Author: michaelficarra

lib/coffee-script/lexer.js

@@ -209,6 +209,7 @@ exports.Lexer = class Lexer
     [heregex, body, flags] = match
     if 0 > body.indexOf '#{'
       re = body.replace(HEREGEX_OMIT, '').replace(/\//g, '\\/')
+      if re.match /^\*/ then @error 'regular expressions cannot begin with `*`'
       @token 'REGEX', "/#{ re or '(?:)' }/#{flags}"
       return heregex.length
     @token 'IDENTIFIER', 'RegExp'

src/lexer.coffee

@@ -52,3 +52,6 @@ test "a heregex will ignore whitespace and comments", ->
 
 test "an empty heregex will compile to an empty, non-capturing group", ->
   eq /(?:)/ + '', ///  /// + ''
+
+test "#1724: regular expressions beginning with `*`", ->
+  throws -> CoffeeScript.compile '/// * ///'