[GR-18163] Simplify String#-@

PullRequest: truffleruby/3403

Author: andrykonchin

spec/ruby/core/string/shared/dedup.rb

@@ -38,6 +38,16 @@
     dynamic.send(@method).should equal("this string is frozen".send(@method).freeze)
   end
 
+  it "does not deduplicate a frozen string when it has instance variables" do
+    dynamic = %w(this string is frozen).join(' ')
+    dynamic.instance_variable_set(:@a, 1)
+    dynamic.freeze
+
+    dynamic.send(@method).should_not equal("this string is frozen".freeze)
+    dynamic.send(@method).should_not equal("this string is frozen".send(@method).freeze)
+    dynamic.send(@method).should equal(dynamic)
+  end
+
   ruby_version_is "3.0" do
     it "interns the provided string if it is frozen" do
       dynamic = "this string is unique and frozen #{rand}".freeze

src/main/java/org/truffleruby/core/kernel/KernelNodes.java

@@ -1150,6 +1150,29 @@ protected RubyArray instanceVariables(Object self) {
 
     }
 
+    @Primitive(name = "any_instance_variable?")
+    public abstract static class AnyInstanceVariableNode extends PrimitiveArrayArgumentsNode {
+
+        @Specialization(limit = "getDynamicObjectCacheLimit()")
+        protected boolean any(RubyDynamicObject self,
+                @CachedLibrary("self") DynamicObjectLibrary objectLibrary) {
+            Object[] keys = objectLibrary.getKeyArray(self);
+
+            for (Object key : keys) {
+                if (key instanceof String) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        @Specialization(guards = "!isRubyDynamicObject(self)")
+        protected boolean noVariablesInImmutableObject(Object self) {
+            return false;
+        }
+    }
+
     @CoreMethod(names = { "is_a?", "kind_of?" }, required = 1)
     public abstract static class KernelIsANode extends CoreMethodArrayArgumentsNode {
 

src/main/ruby/truffleruby/core/string.rb

@@ -1247,7 +1247,7 @@ def -@
     str = frozen? ? self : dup.freeze
     if Primitive.string_interned?(self)
       self
-    elsif !(str.instance_variables).empty?
+    elsif Primitive.any_instance_variable?(str)
       str
     else
       Primitive.string_intern(str)