Pop stack when rule is pushed without position advancement

Previously only the scope name was checked which allowed cases
were rules without scope names to grow the stack infinitely without
advancing the position.

Closes atom/language-ruby-on-rails#1

spec/text-mate-grammar-spec.coffee

@@ -635,11 +635,9 @@ describe "TextMateGrammar", ->
         expect(lastToken.value).toEqual ';'
 
     describe "HTML (Ruby - ERB)", ->
-      beforeEach ->
+      it "correctly parses strings inside tags", ->
         grammar = atom.syntax.selectGrammar('page.erb')
         lines = grammar.tokenizeLines '<% page_title "My Page" %>'
-
-      it "correctly parses strings inside tags", ->
         tokens = lines[0]
 
         expect(tokens[2].value).toEqual '"'
@@ -649,6 +647,16 @@ describe "TextMateGrammar", ->
         expect(tokens[4].value).toEqual '"'
         expect(tokens[4].scopes).toEqual ["text.html.erb", "meta.embedded.line.erb", "string.quoted.double.ruby", "punctuation.definition.string.end.ruby"]
 
+      it "does not loop infinitely on <%>", ->
+        atom.packages.activatePackage('language-html', sync: true)
+        atom.packages.activatePackage('language-ruby-on-rails', sync: true)
+
+        grammar = atom.syntax.selectGrammar('foo.html.erb')
+        [tokens] = grammar.tokenizeLines '<%>'
+        expect(tokens.length).toBe 1
+        expect(tokens[0].value).toEqual '<%>'
+        expect(tokens[0].scopes).toEqual ["text.html.erb"]
+
     describe "Unicode support", ->
       describe "Surrogate pair characters", ->
         beforeEach ->

src/text-mate-grammar.coffee

@@ -157,7 +157,16 @@ class TextMateGrammar
           ruleStack.pop()
         else if ruleStack.length > previousRuleStackLength # Stack size increased with zero length match
           [penultimateRule, lastRule] = ruleStack[-2..]
+
+          # Same exact rule was pushed but position wasn't advanced
+          if lastRule? and lastRule == penultimateRule
+            popStack = true
+
+          # Rule with same scope name as previous rule was pushed but position wasn't advanced
           if lastRule?.scopeName? and penultimateRule.scopeName == lastRule.scopeName
+            popStack = true
+
+          if popStack
             ruleStack.pop()
             tokens.push(new Token(
               value: line[position...line.length]