Allow for escaped ] characters in [] IDs

Allows for ] literal characters to be used within [] IDs by prefixing them with the \ character. `\` literal at the end of the  may be referenced by the `\\` sequence if conflicting. Under most circumstances the `\\` sequence will continue to work.

Potentially breaking change for users of [] ids that have `\\` anywhere in the id or `\` at the end of the id.

Fixes #1092

spec/parser.js

@@ -39,6 +39,12 @@ describe('parser', function() {
   it('parses mustaches with - in a path', function() {
     equals(astFor('{{foo-bar}}'), '{{ PATH:foo-bar [] }}\n');
   });
+  it('parses mustaches with escaped [] in a path', function() {
+    equals(astFor('{{[foo[\\]]}}'), '{{ PATH:foo[] [] }}\n');
+  });
+  it('parses escaped \\\\ in path', function() {
+    equals(astFor('{{[foo\\\\]}}'), '{{ PATH:foo\\ [] }}\n');
+  });
 
   it('parses mustaches with parameters', function() {
     equals(astFor('{{foo bar}}'), '{{ PATH:foo [PATH:bar] }}\n');

spec/tokenizer.js

@@ -146,6 +146,11 @@ describe('Tokenizer', function() {
     shouldMatchTokens(result, ['OPEN', 'ID', 'SEP', 'ID', 'CLOSE', 'OPEN', 'ID', 'SEP', 'ID', 'CLOSE']);
   });
 
+  it('allows escaped literals in []', function() {
+    var result = tokenize('{{foo.[bar\\]]}}');
+    shouldMatchTokens(result, ['OPEN', 'ID', 'SEP', 'ID', 'CLOSE']);
+  });
+
   it('tokenizes {{.}} as OPEN ID CLOSE', function() {
     var result = tokenize('{{.}}');
     shouldMatchTokens(result, ['OPEN', 'ID', 'CLOSE']);

src/handlebars.l

@@ -120,7 +120,7 @@ ID    [^\s!"#%-,\.\/;->@\[-\^`\{-~]+/{LOOKAHEAD}
 
 <mu>{ID}                         return 'ID';
 
-<mu>'['[^\]]*']'                 return 'ID';
+<mu>'['('\\]'|[^\]])*']'         yytext = yytext.replace(/\\([\\\]])/g,'$1'); return 'ID';
 <mu>.                            return 'INVALID';
 
 <INITIAL,mu><<EOF>>              return 'EOF';