Add undefined and null literal support

This adds the UndefinedLiteral and NullLiteral to AST.

Fixes #990

12 files changed, 65 insertions, 2 deletions

diff --git a/docs/compiler-api.md b/docs/compiler-api.md
index 40ded8f..c09414f 100644
--- a/docs/compiler-api.md
+++ b/docs/compiler-api.md
@@ -164,6 +164,14 @@ interface NumberLiteral <: Literal {
     value: number;
     original: number;
 }
+
+interface UndefinedLiteral <: Literal {
+    type: "UndefinedLiteral";
+}
+
+interface NullLiteral <: Literal {
+    type: "NullLiteral";
+}
 ```
 
 
diff --git a/lib/handlebars/compiler/ast.js b/lib/handlebars/compiler/ast.js
index 45212b3..e5904c6 100644
--- a/lib/handlebars/compiler/ast.js
+++ b/lib/handlebars/compiler/ast.js
@@ -101,6 +101,18 @@ var AST = {
       this.value = bool === 'true';
   },
 
+  UndefinedLiteral: function(locInfo) {
+    this.loc = locInfo;
+    this.type = 'UndefinedLiteral';
+    this.original = this.value = undefined;
+  },
+
+  NullLiteral: function(locInfo) {
+    this.loc = locInfo;
+    this.type = 'NullLiteral';
+    this.original = this.value = null;
+  },
+
   Hash: function(pairs, locInfo) {
     this.loc = locInfo;
     this.type = 'Hash';
diff --git a/lib/handlebars/compiler/compiler.js b/lib/handlebars/compiler/compiler.js
index e1b4dfb..a39082d 100644
--- a/lib/handlebars/compiler/compiler.js
+++ b/lib/handlebars/compiler/compiler.js
@@ -273,6 +273,14 @@ Compiler.prototype = {
     this.opcode('pushLiteral', bool.value);
   },
 
+  UndefinedLiteral: function() {
+    this.opcode('pushLiteral', 'undefined');
+  },
+
+  NullLiteral: function() {
+    this.opcode('pushLiteral', 'null');
+  },
+
   Hash: function(hash) {
     var pairs = hash.pairs, i, l;
 
diff --git a/lib/handlebars/compiler/printer.js b/lib/handlebars/compiler/printer.js
index 55232cc..dcc73c3 100644
--- a/lib/handlebars/compiler/printer.js
+++ b/lib/handlebars/compiler/printer.js
@@ -124,6 +124,14 @@ PrintVisitor.prototype.BooleanLiteral = function(bool) {
   return "BOOLEAN{" + bool.value + "}";
 };
 
+PrintVisitor.prototype.UndefinedLiteral = function() {
+  return 'UNDEFINED';
+};
+
+PrintVisitor.prototype.NullLiteral = function() {
+  return 'NULL';
+};
+
 PrintVisitor.prototype.Hash = function(hash) {
   var pairs = hash.pairs;
   var joinedPairs = [];
diff --git a/lib/handlebars/compiler/visitor.js b/lib/handlebars/compiler/visitor.js
index 4101a4f..6e4168e 100644
--- a/lib/handlebars/compiler/visitor.js
+++ b/lib/handlebars/compiler/visitor.js
@@ -110,6 +110,8 @@ Visitor.prototype = {
   StringLiteral: function(/* string */) {},
   NumberLiteral: function(/* number */) {},
   BooleanLiteral: function(/* bool */) {},
+  UndefinedLiteral: function(/* literal */) {},
+  NullLiteral: function(/* literal */) {},
 
   Hash: function(hash) {
     this.acceptArray(hash.pairs);
diff --git a/spec/basic.js b/spec/basic.js
index 9b6678a..11002e4 100644
--- a/spec/basic.js
+++ b/spec/basic.js
@@ -66,6 +66,16 @@ describe("basic context", function() {
     shouldCompileTo('val: {{{val1/val2}}}', {val1: {val2: false}}, 'val: false');
   });
 
+  it('should handle undefined and null', function() {
+    shouldCompileTo('{{awesome undefined null}}',
+        {
+          awesome: function(_undefined, _null, options) {
+            return (_undefined === undefined) + ' ' + (_null === null) + ' ' + (typeof options);
+          }
+        },
+        'true true object');
+  });
+
   it("newlines", function() {
       shouldCompileTo("Alan's\nTest", {}, "Alan's\nTest");
       shouldCompileTo("Alan's\rTest", {}, "Alan's\rTest");
diff --git a/spec/javascript-compiler.js b/spec/javascript-compiler.js
index fb78658..f47ddeb 100644
--- a/spec/javascript-compiler.js
+++ b/spec/javascript-compiler.js
@@ -23,7 +23,7 @@ describe('javascript-compiler api', function() {
     // Tests nameLookup dot vs. bracket behavior.  Bracket is required in certain cases
     // to avoid errors in older browsers.
     it('should handle reserved words', function() {
-      shouldCompileTo("{{foo}} {{~null~}}", { foo: "food" }, "food");
+      shouldCompileTo("{{foo}} {{~[null]~}}", { foo: "food" }, "food");
     });
   });
   describe('#compilerInfo', function() {
diff --git a/spec/parser.js b/spec/parser.js
index 3d3dccf..6f5a660 100644
--- a/spec/parser.js
+++ b/spec/parser.js
@@ -58,6 +58,10 @@ describe('parser', function() {
     equals(ast_for("{{foo false}}"), "{{ PATH:foo [BOOLEAN{false}] }}\n");
   });
 
+  it('parses mustaches with undefined and null parameters', function() {
+    equals(ast_for("{{foo undefined null}}"), "{{ PATH:foo [UNDEFINED, NULL] }}\n");
+  });
+
   it('parses mutaches with DATA parameters', function() {
     equals(ast_for("{{foo @bar}}"), "{{ PATH:foo [@PATH:bar] }}\n");
   });
diff --git a/spec/tokenizer.js b/spec/tokenizer.js
index 0a5143b..26a1c3b 100644
--- a/spec/tokenizer.js
+++ b/spec/tokenizer.js
@@ -322,6 +322,13 @@ describe('Tokenizer', function() {
     shouldBeToken(result[2], "BOOLEAN", "false");
   });
 
+  it('tokenizes undefined and null', function() {
+    var result = tokenize('{{ foo undefined null }}');
+    shouldMatchTokens(result, ['OPEN', 'ID', 'UNDEFINED', 'NULL', 'CLOSE']);
+    shouldBeToken(result[2], 'UNDEFINED', 'undefined');
+    shouldBeToken(result[3], 'NULL', 'null');
+  });
+
   it('tokenizes hash arguments', function() {
     var result = tokenize("{{ foo bar=baz }}");
     shouldMatchTokens(result, ['OPEN', 'ID', 'ID', 'EQUALS', 'ID', 'CLOSE']);
diff --git a/spec/visitor.js b/spec/visitor.js
index 3217230..8b9ef9f 100644
--- a/spec/visitor.js
+++ b/spec/visitor.js
@@ -9,7 +9,7 @@ describe('Visitor', function() {
     // Simply run the thing and make sure it does not fail and that all of the
     // stub methods are executed
     var visitor = new Handlebars.Visitor();
-    visitor.accept(Handlebars.parse('{{foo}}{{#foo (bar 1 "1" true) foo=@data}}{{!comment}}{{> bar }} {{/foo}}'));
+    visitor.accept(Handlebars.parse('{{foo}}{{#foo (bar 1 "1" true undefined null) foo=@data}}{{!comment}}{{> bar }} {{/foo}}'));
   });
 
   it('should traverse to stubs', function() {
diff --git a/src/handlebars.l b/src/handlebars.l
index ace0263..55d8efc 100644
--- a/src/handlebars.l
+++ b/src/handlebars.l
@@ -102,6 +102,8 @@ ID    [^\s!"#%-,\.\/;->@\[-\^`\{-~]+/{LOOKAHEAD}
 <mu>"@"                          return 'DATA';
 <mu>"true"/{LITERAL_LOOKAHEAD}   return 'BOOLEAN';
 <mu>"false"/{LITERAL_LOOKAHEAD}  return 'BOOLEAN';
+<mu>"undefined"/{LITERAL_LOOKAHEAD} return 'UNDEFINED';
+<mu>"null"/{LITERAL_LOOKAHEAD}   return 'NULL';
 <mu>\-?[0-9]+(?:\.[0-9]+)?/{LITERAL_LOOKAHEAD} return 'NUMBER';
 <mu>"as"\s+"|"                   return 'OPEN_BLOCK_PARAMS';
 <mu>"|"                          return 'CLOSE_BLOCK_PARAMS';
diff --git a/src/handlebars.yy b/src/handlebars.yy
index 18f03b9..d724578 100644
--- a/src/handlebars.yy
+++ b/src/handlebars.yy
@@ -83,6 +83,8 @@ partial
 param
   : helperName -> $1
   | sexpr -> $1
+  | UNDEFINED -> new yy.UndefinedLiteral(yy.locInfo(@$))
+  | NULL -> new yy.NullLiteral(yy.locInfo(@$))
   ;
 
 sexpr