Fix recursive raising FrozenError

Author: andrykonchin

CHANGELOG.md

@@ -15,6 +15,7 @@ Bug fixes:
 * Run context cleanup such as showing the output of tools when `SignalException` and `Interrupt` escape (@eregon).
 * Handle a new variable inside the `case` target expression correctly (#3377, @eregon).
 * The arguments of `Thread.new(*args, &block)` need to be marked as shared between multiple threads (#3179, @eregon).
+* Fix recursive raising `FrozenError` exception when redefined `#inspect` modifies an object (#3388, @andrykonchin).
 
 Compatibility:
 

spec/ruby/core/exception/frozen_error_spec.rb

@@ -20,3 +20,19 @@ def o.x; end
     end
   end
 end
+
+describe "Modifying a frozen object" do
+  context "#inspect is redefined and modifies the object" do
+    it "returns ... instead of String representation of object" do
+      object = Object.new
+      def object.inspect; @a = 1 end
+      def object.modify; @a = 2 end
+
+      object.freeze
+
+      # CRuby's message contains multiple whitespaces before '...'.
+      # So handle both multiple and single whitespace.
+      -> { object.modify }.should raise_error(FrozenError, /can't modify frozen .*?: \s*.../)
+    end
+  end
+end

src/main/java/org/truffleruby/core/exception/CoreExceptions.java

@@ -118,6 +118,13 @@ public String inspectReceiver(Object receiver) {
         return RubyGuards.getJavaString(rubyString);
     }
 
+    @TruffleBoundary
+    public String inspectFrozenObject(Object object) {
+        Object rubyString = DispatchNode.getUncached().call(
+                context.getCoreLibrary().truffleExceptionOperationsModule, "inspect_frozen_object", object);
+        return RubyGuards.getJavaString(rubyString);
+    }
+
     // ArgumentError
 
     public RubyException argumentErrorOneHashRequired(RubyBaseNode currentNode) {
@@ -295,7 +302,8 @@ public RubyException argumentErrorCantUnfreeze(Object self, Node currentNode) {
     @TruffleBoundary
     public RubyException frozenError(Object object, Node currentNode) {
         String className = LogicalClassNode.getUncached().execute(object).fields.getName();
-        return frozenError(StringUtils.format("can't modify frozen %s: %s", className, inspect(object)), currentNode,
+        String string = inspectFrozenObject(object);
+        return frozenError(StringUtils.format("can't modify frozen %s: %s", className, string), currentNode,
                 object);
     }
 

src/main/ruby/truffleruby/core/truffle/exception_operations.rb

@@ -91,6 +91,17 @@ def self.receiver_string(receiver)
       end
     end
 
+    # MRI: inspect_frozen_obj
+    def self.inspect_frozen_object(object)
+      string = nil
+
+      return '...' if Truffle::ThreadOperations.detect_recursion object do
+        string = Truffle::Type.rb_inspect(object)
+      end
+
+      string
+    end
+
     # default implementation of Exception#detailed_message hook
     def self.detailed_message(exception, highlight)
       message = StringValue exception.message.to_s