Another attempt to fix #1150

Here's how the algorithm in balancedString() was modified.  When we
encounter a slash in an interpolation, we:

    * try to find a heregex right after it; if found---skip it.  Three
      slashes always terminate a heregex, no matter if there is an open
      "#{" before them or not, so we don't have to bother about
      sub-interpolations inside the heregex.

    * try to find a regex right after it; if found---skip it.  Simple
      regexen can't contain interpolations.

    * otherwise, assume that the slash means division and carry on.

lib/lexer.js

@@ -461,7 +461,7 @@
       throw SyntaxError("Reserved word \"" + (this.value()) + "\" on line " + (this.line + 1) + " can't be assigned");
     };
     Lexer.prototype.balancedString = function(str, end) {
-      var i, letter, prev, stack, _ref2;
+      var i, letter, match, prev, stack, _ref2;
       stack = [end];
       for (i = 1, _ref2 = str.length; 1 <= _ref2 ? i < _ref2 : i > _ref2; 1 <= _ref2 ? i++ : i--) {
         switch (letter = str.charAt(i)) {
@@ -478,6 +478,8 @@
         }
         if (end === '}' && (letter === '"' || letter === "'")) {
           stack.push(end = letter);
+        } else if (end === '}' && letter === '/' && (match = HEREGEX.exec(str.slice(i)) || REGEX.exec(str.slice(i)))) {
+          i += match[0].length - 1;
         } else if (end === '}' && letter === '{') {
           stack.push(end = '}');
         } else if (end === '"' && prev === '#' && letter === '{') {

src/lexer.coffee

@@ -414,6 +414,8 @@ exports.Lexer = class Lexer
           continue
       if end is '}' and letter in ['"', "'"]
         stack.push end = letter
+      else if end is '}' and letter is '/' and match = (HEREGEX.exec(str.slice i) or REGEX.exec(str.slice i))
+        i += match[0].length - 1
       else if end is '}' and letter is '{'
         stack.push end = '}'
       else if end is '"' and prev is '#' and letter is '{'

test/interpolation.coffee

@@ -20,6 +20,19 @@ eq "#{ "{" }", "{"
 eq "#{ '#{}}' } }", '#{}} }'
 eq "#{"'#{ ({a: "b#{1}"}['a']) }'"}", "'b1'"
 
+# Issue #1150: String interpolation regression
+eq "#{'"/'}",                '"/'
+eq "#{"/'"}",                "/'"
+eq "#{/'"/}",                '/\'"/'
+eq "#{"'/" + '/"' + /"'/}",  '\'//"/"\'/'
+eq "#{"'/"}#{'/"'}#{/"'/}",  '\'//"/"\'/'
+eq "#{6 / 2}",               '3'
+eq "#{6 / 2}#{6 / 2}",       '33' # parsed as division
+eq "#{6 + /2}#{6/ + 2}",     '6/2}#{6/2' # parsed as a regex
+eq "#{6/2}
+    #{6/2}",                 '3    3' # newline cannot be part of a regex, so it's division
+eq "#{/// "'/'"/" ///}",     '/"\'\\/\'"\\/"/' # heregex, stuffed with spicy characters
+
 hello = 'Hello'
 world = 'World'
 ok '#{hello} #{world}!' is '#{hello} #{world}!'