[Ruby 3.0 support] Don't warn when uninitialized instance variable is accessed

CHANGELOG.md

@@ -19,6 +19,7 @@ Compatibility:
 * `Module#attr_*` methods now return an array of method names (#2498, @gogainda).
 * Fixed `Socket#(local|remote)_address` to retrieve family and type from the file descriptor (#2444, @larskanis).
 * Add `Thread.ignore_deadlock` accessor (#2453).
+* Do not warn when uninitialized instance variable is accessed (#2502, @andrykonchin).
 
 Performance:
 

spec/ruby/language/variables_spec.rb

@@ -822,3 +822,32 @@ def test
     result.should == 1
   end
 end
+
+describe "Instance variables" do
+  context "when instance variable is uninitialized" do
+    ruby_version_is ""..."3.0" do
+      it "warns about accessing uninitialized instance variable" do
+        obj = Object.new
+        def obj.foobar; a = @a; end
+
+        -> { obj.foobar }.should complain(/warning: instance variable @a not initialized/, verbose: true)
+      end
+    end
+
+    ruby_version_is "3.0" do
+      it "doesn't warn about accessing uninitialized instance variable" do
+        obj = Object.new
+        def obj.foobar; a = @a; end
+
+        -> { obj.foobar }.should_not complain(verbose: true)
+      end
+    end
+
+    it "doesn't warn at lazy initialization" do
+      obj = Object.new
+      def obj.foobar; @a ||= 42; end
+
+      -> { obj.foobar }.should_not complain(verbose: true)
+    end
+  end
+end

src/main/java/org/truffleruby/language/objects/ReadInstanceVariableNode.java

@@ -15,10 +15,8 @@
 import org.truffleruby.language.RubyContextSourceNode;
 import org.truffleruby.language.RubyDynamicObject;
 import org.truffleruby.language.RubyNode;
-import org.truffleruby.language.WarningNode;
 
 import com.oracle.truffle.api.CompilerDirectives;
-import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.object.DynamicObjectLibrary;
 import com.oracle.truffle.api.profiles.ConditionProfile;
@@ -29,7 +27,6 @@ public class ReadInstanceVariableNode extends RubyContextSourceNode {
 
     @Child private RubyNode receiver;
     @Child private DynamicObjectLibrary objectLibrary;
-    @Child private WarningNode warningNode;
 
     private final ConditionProfile objectProfile = ConditionProfile.create();
 
@@ -45,20 +42,12 @@ public Object execute(VirtualFrame frame) {
         if (objectProfile.profile(receiverObject instanceof RubyDynamicObject)) {
             final DynamicObjectLibrary objectLibrary = getObjectLibrary();
             final RubyDynamicObject dynamicObject = (RubyDynamicObject) receiverObject;
-            if (!objectLibrary.containsKey(dynamicObject, name)) {
-                warnNotInitialized();
-            }
             return objectLibrary.getOrDefault(dynamicObject, name, nil);
         } else {
             return nil;
         }
     }
 
-    @TruffleBoundary
-    private String getWarningMessage() {
-        return String.format("instance variable %s not initialized", name);
-    }
-
     @Override
     public Object isDefined(VirtualFrame frame, RubyLanguage language, RubyContext context) {
         final Object receiverObject = receiver.execute(frame);
@@ -87,15 +76,4 @@ private DynamicObjectLibrary getObjectLibrary() {
         return objectLibrary;
     }
 
-    private void warnNotInitialized() {
-        if (warningNode == null) {
-            CompilerDirectives.transferToInterpreterAndInvalidate();
-            warningNode = insert(new WarningNode());
-        }
-
-        if (warningNode.shouldWarn()) {
-            warningNode.warningMessage(getSourceSection(), getWarningMessage());
-        }
-    }
-
 }

src/main/java/org/truffleruby/parser/BodyTranslator.java

@@ -2424,8 +2424,6 @@ public RubyNode visitOpAsgnOrNode(OpAsgnOrParseNode node) {
         RubyNode rhs = node.getSecondNode().accept(this);
 
         // This is needed for class variables. Constants are handled separately in visitOpAsgnConstDeclNode.
-        // It is also needed for instance variables to prevent attempted read which may trigger "not initialized"
-        // warnings unintentionally.
         if (node.getFirstNode().needsDefinitionCheck()) {
             RubyNode defined = new DefinedNode(lhs);
             lhs = new AndNode(defined, lhs);

src/main/java/org/truffleruby/parser/ast/InstVarParseNode.java

@@ -80,4 +80,9 @@ public List<ParseNode> childNodes() {
     public void setName(String name) {
         this.name = name;
     }
+
+    @Override
+    public boolean needsDefinitionCheck() {
+        return false;
+    }
 }