[Truffle] Don't taint from self in String#[](String).

Author: nirvdrum

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

@@ -1,4 +1,3 @@
 fails:String#[] with Range calls to_int on range arguments
 fails:String#[] with Range works with Range subclasses
 fails:String#[] with Regexp, index returns nil if there is no capture for the given index
-fails:String#[] with String taints resulting strings when other is tainted

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

@@ -1,7 +1,6 @@
 fails:String#slice with Range calls to_int on range arguments
 fails:String#slice with Range works with Range subclasses
 fails:String#slice with Regexp, index returns nil if there is no capture for the given index
-fails:String#slice with String taints resulting strings when other is tainted
 fails:String#slice! with index calls to_int on index
 fails:String#slice! with index returns the character given by the character index
 fails:String#slice! with index, length deletes and returns the substring at idx and the given length

truffle/src/main/java/org/jruby/truffle/nodes/cast/TaintResultNode.java

@@ -12,6 +12,7 @@
 
 import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.ControlFlowException;
 import com.oracle.truffle.api.nodes.ExplodeLoop;
 import com.oracle.truffle.api.nodes.UnexpectedResultException;
 import com.oracle.truffle.api.source.SourceSection;
@@ -70,6 +71,8 @@ public Object execute(VirtualFrame frame) {
 
         try {
             result = method.executeRubyBasicObject(frame);
+        } catch (DoNotTaintException e) {
+            return e.getResult();
         } catch (UnexpectedResultException e) {
             throw new UnsupportedOperationException(e);
         }
@@ -97,4 +100,18 @@ public Object execute(VirtualFrame frame) {
 
         return result;
     }
+
+    public static class DoNotTaintException extends ControlFlowException {
+        private static final long serialVersionUID = 5321304910918469059L;
+
+        private final Object result;
+
+        public DoNotTaintException(Object result) {
+            this.result = result;
+        }
+
+        public Object getResult() {
+            return result;
+        }
+    }
 }

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

@@ -612,7 +612,7 @@ public Object slice(VirtualFrame frame, RubyString string, RubyString matchStr,
                     dupNode = insert(DispatchHeadNodeFactory.createMethodCall(getContext()));
                 }
 
-                return dupNode.call(frame, matchStr, "dup", null);
+                throw new TaintResultNode.DoNotTaintException(dupNode.call(frame, matchStr, "dup", null));
             }
 
             return nil();