The tokenizer shouldn't get into an infinite loop in certain termination conditions

lib/handlebars/jison_ext.js

@@ -5,23 +5,30 @@ Handlebars.Lexer = function() {};
 Handlebars.Lexer.prototype = {
   setInput: function(input) {
     this.input = input;
+    this.matched = this.match = '';
     this.yylineno = 0;
   },
 
   setupLex: function() {
     this.yyleng = 0;
     this.yytext = '';
+    this.match = '';
+    this.readchars = 0;
   },
 
   getchar: function(n) {
     n = n || 1;
-    var char = "";
+    var chars = "", char = "";
 
     for(var i=0; i<n; i++) {
-      char += this.input[0];
-      this.yytext += this.input[0];
+      char = this.input[0];
+      chars += char;
+      this.yytext += char;
       this.yyleng++;
 
+      this.matched += char;
+      this.match += char;
+
       if(char === "\n") this.yylineno++;
 
       this.input = this.input.slice(1);
@@ -29,21 +36,48 @@ Handlebars.Lexer.prototype = {
     return char;
   },
 
-  readchar: function(n) {
+  readchar: function(n, ignore) {
     n = n || 1;
     var char;
 
     for(var i=0; i<n; i++) {
       char = this.input[i];
       if(char === "\n") this.yylineno++;
+
+      this.matched += char;
+      this.match += char;
+      if(ignore) { this.readchars++; }
     }
 
     this.input = this.input.slice(n);
   },
 
+  ignorechar: function(n) {
+    this.readchar(n, true);
+  },
+
   peek: function(n) {
     return this.input.slice(0, n || 1);
-  }
+  },
+
+  pastInput:function () {
+    var past = this.matched.substr(0, this.matched.length - this.match.length);
+    return (past.length > 20 ? '...':'') + past.substr(-20).replace(/\n/g, "");
+  },
+
+  upcomingInput:function () {
+    var next = this.match;
+    if (next.length < 20) {
+      next += this.input.substr(0, 20-next.length);
+    }
+    return (next.substr(0,20)+(next.length > 20 ? '...':'')).replace(/\n/g, "");
+  },
+
+  showPosition:function () {
+    var pre = this.pastInput();
+    var c = new Array(pre.length + 1 + this.readchars).join("-");
+    return pre + this.upcomingInput() + "\n" + c+"^";
+  },
 };
 
 Handlebars.Visitor = function() {};