Turn ALLOW_TO_STRING into a debug flag as in most cases it's OK to store the byte[]

* And preventing {RubyString,Rope}#toString() calls is really challenging
  and does not seem worth it.

(cherry picked from commit b4fcc2c)

Author: eregon

src/main/java/org/truffleruby/core/rope/ManagedRope.java

@@ -54,12 +54,14 @@ public final byte[] getBytes() {
 
     @Override
     public final String toString() {
-        assert ALLOW_TO_STRING;
-
-        final byte[] bytesBefore = bytes;
-        final String string = RopeOperations.decodeOrEscapeBinaryRope(this, RopeOperations.flattenBytes(this));
-        assert bytes == bytesBefore : "bytes should not be modified by Rope#toString() as otherwise inspecting a Rope would have a side effect";
-        return string;
+        if (DEBUG_ROPE_BYTES) {
+            final byte[] bytesBefore = bytes;
+            final String string = RopeOperations.decodeOrEscapeBinaryRope(this, RopeOperations.flattenBytes(this));
+            assert bytes == bytesBefore : "bytes should not be modified by Rope#toString() as otherwise inspecting a Rope would have a side effect";
+            return string;
+        } else {
+            return RopeOperations.decodeRope(this);
+        }
     }
 
 }

src/main/java/org/truffleruby/core/rope/NativeRope.java

@@ -184,7 +184,6 @@ public int hashCode() {
 
     @Override
     public String toString() {
-        assert ALLOW_TO_STRING;
         return toLeafRope().toString();
     }
 

src/main/java/org/truffleruby/core/rope/Rope.java

@@ -20,8 +20,8 @@ public abstract class Rope implements Comparable<Rope> {
     // NativeRope, RepeatingRope, 3 LeafRope, ConcatRope, SubstringRope, 1 LazyRope
     public static final int NUMBER_OF_CONCRETE_CLASSES = 8;
 
-    // Useful for debugging. Setting to false allow to catch wrong usages.
-    protected static final boolean ALLOW_TO_STRING = false;
+    // Useful for debugging. Setting to true avoids ManagedRope#toString to populate bytes as a side-effect of the debugger calling toString().
+    protected static final boolean DEBUG_ROPE_BYTES = false;
 
     public final Encoding encoding;
     private final int byteLength;