[Truffle] - String#downcase! and #capitalize! raise an exception when self is frozen

Author: lucasallan

spec/truffle/tags/core/string/capitalize_tags.txt

@@ -1,4 +1,3 @@
 fails:String#capitalize taints resulting string when self is tainted
 fails:String#capitalize is locale insensitive (only upcases a-z and only downcases A-Z)
-fails:String#capitalize returns subclass instances when called on a subclass
-fails:String#capitalize! raises a RuntimeError when self is frozen
+fails:String#capitalize returns subclass instances when called on a subclass

spec/truffle/tags/core/string/downcase_tags.txt

@@ -1,4 +1,3 @@
 fails:String#downcase is locale insensitive (only replaces A-Z)
 fails:String#downcase taints result when self is tainted
 fails:String#downcase returns a subclass instance for subclasses
-fails:String#downcase! raises a RuntimeError when self is frozen

truffle/src/main/java/org/jruby/truffle/nodes/core/StringNodes.java

@@ -774,12 +774,11 @@ public DowncaseBangNode(DowncaseBangNode prev) {
         public RubyBasicObject downcase(RubyString string) {
             notDesignedForCompilation();
 
+            string.checkFrozen(this);
             ByteList newByteList = StringNodesHelper.downcase(string);
 
             if (newByteList.equal(string.getBytes())) {
                 return getContext().getCoreLibrary().getNilObject();
-            } else if (string.isFrozen()) {
-                throw new RaiseException(getContext().getCoreLibrary().runtimeError("can't modify frozen string", this));
             } else {
                 string.set(newByteList);
                 return string;
@@ -1925,11 +1924,12 @@ public CapitalizeBangNode(CapitalizeBangNode prev) {
         @Specialization
         public RubyBasicObject capitalizeBang(RubyString string) {
             notDesignedForCompilation();
+
+            string.checkFrozen(this);
             String javaString = string.toString();
+
             if (javaString.isEmpty()) {
                 return getContext().getCoreLibrary().getNilObject();
-            } else if (string.isFrozen()) {
-                throw new RaiseException(getContext().getCoreLibrary().runtimeError("can't modify frozen string", this));
             } else {
                 final ByteList byteListString = StringNodesHelper.capitalize(string);