Parse and output ES6 template strings. Yikes!

lib/ast.js

@@ -501,6 +501,22 @@ var AST_Destructuring = DEFNODE("Destructuring", "names is_array", {
     }
 });
 
+var AST_TemplateString = DEFNODE("TemplateString", "segments", {
+    $documentation: "A template string literal",
+    $propdoc: {
+        segments: "[string|AST_Expression]* One or more segments. They can be the parts that are evaluated, or the raw string parts."
+    },
+    _walk: function(visitor) {
+        return visitor._visit(this, function(){
+            this.segments.forEach(function(seg, i){
+                if (i % 2 !== 0) {
+                    seg._walk(visitor);
+                }
+            });
+        });
+    }
+});
+
 /* -----[ JUMPS ]----- */
 
 var AST_Jump = DEFNODE("Jump", null, {

lib/output.js

@@ -776,6 +776,20 @@ function OutputStream(options) {
         self._do_print(output);
     });
 
+    DEFPRINT(AST_TemplateString, function(self, output) {
+        output.print("`");
+        for (var i = 0; i < self.segments.length; i++) {
+            if (typeof self.segments[i] !== "string") {
+                output.print("${");
+                self.segments[i].print(output);
+                output.print("}");
+            } else {
+                output.print(self.segments[i]);
+            }
+        }
+        output.print("`");
+    });
+
     AST_Arrow.DEFMETHOD("_do_print", function(output){
         var self = this;
         var parent = output.parent();

lib/parse.js

@@ -114,7 +114,7 @@ var WHITESPACE_CHARS = makePredicate(characters(" \u00a0\n\r\t\f\u000b\u200b\u18
 
 var PUNC_BEFORE_EXPRESSION = makePredicate(characters("[{(,.;:"));
 
-var PUNC_CHARS = makePredicate(characters("[]{}(),;:"));
+var PUNC_CHARS = makePredicate(characters("[]{}(),;:`"));
 
 var REGEXP_MODIFIERS = makePredicate(characters("gmsiy"));
 
@@ -595,6 +595,9 @@ function tokenizer($TEXT, filename, html5_comments) {
         parse_error("Unexpected character '" + ch + "'");
     };
 
+    next_token.next = next;
+    next_token.peek = peek;
+
     next_token.context = function(nc) {
         if (nc) S = nc;
         return S;
@@ -805,6 +808,7 @@ function parse($TEXT, options) {
                 });
               case "[":
               case "(":
+              case "`":
                 return simple_statement();
               case ";":
                 next();
@@ -1336,6 +1340,8 @@ function parse($TEXT, options) {
                 return subscripts(array_(), allow_calls);
               case "{":
                 return subscripts(object_or_object_destructuring_(), allow_calls);
+              case "`":
+                return subscripts(template_string(), allow_calls);
             }
             unexpected();
         }
@@ -1352,6 +1358,38 @@ function parse($TEXT, options) {
         unexpected();
     };
 
+    function template_string() {
+        var tokenizer_S = S.input, start = S.token, segments = [], segment = "", ch;
+
+        while ((ch = tokenizer_S.next()) !== "`")  {
+            if (ch === "$" && tokenizer_S.peek() === "{") {
+                segments.push(segment); segment = "";
+                tokenizer_S.next();
+                next();
+                segments.push(expression());
+                expect("}");
+                if (is("punc", "`")) {
+                    break;
+                }
+                continue;
+            }
+            segment += ch;
+            if (ch === "\\") {
+                segment += tokenizer_S.next();
+            }
+        }
+
+        segments.push(segment);
+
+        next();
+
+        return new AST_TemplateString({
+            start: start,
+            segments: segments,
+            end: S.token
+        });
+    }
+
     function expr_list(closing, allow_trailing_comma, allow_empty) {
         var first = true, a = [];
         while (!is("punc", closing)) {

test/compress/harmony.js

@@ -46,6 +46,16 @@ typeof_arrow_functions: {
     expect_exact: "\"function\";"
 }
 
+template_strings: {
+    input: {
+        ``;
+        `xx\`x`;
+        `${ foo + 2 }`;
+        ` foo ${ bar + `baz ${ qux }` }`;
+    }
+    expect_exact: "``;`xx\\`x`;`${foo+2}`;` foo ${bar+`baz ${qux}`}`;";
+}
+
 destructuring_arguments: {
     input: {
         (function ( a ) { });