Merge pull request #1208 from atom/ks-erb-infinite-parse-loop

Prevent infinite loop in erb grammar

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]