[Nestmates] Unnecessary access widening bridge method generated since eclipse-jdt#4197 (eclipse-jdt#4206)

* Fixes eclipse-jdt#4204

Author: srikanth-sankaran

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/ast/TypeDeclaration.java

@@ -1794,14 +1794,14 @@ private final void updateNestRelations() {
 
 	ClassScope outerMostClassScope = this.scope;
 	Scope skope = this.scope;
-
+	boolean concreteType = true;
 	while (skope != null && skope.kind != Scope.COMPILATION_UNIT_SCOPE) {
 		switch (skope.kind) {
 			case Scope.METHOD_SCOPE :
 				ReferenceContext context = ((MethodScope) skope).referenceContext;
 				if (context instanceof LambdaExpression lambdaExpression) {
 					if (lambdaExpression != lambdaExpression.original) // transient unreal universe.
-						return;
+						concreteType = false;
 				}
 				break;
 			case Scope.CLASS_SCOPE:
@@ -1813,8 +1813,11 @@ private final void updateNestRelations() {
 
 	SourceTypeBinding nestHost =  outerMostClassScope != null ? outerMostClassScope.referenceContext.binding : null;
 	if (nestHost != null && !this.binding.equals(nestHost)) {
+		// https://bugs.eclipse.org/bugs/show_bug.cgi?id=572190 && https://github.com/eclipse-jdt/eclipse.jdt.core/issues/4204:
+		// The nest host is valid even for a transient type, but a transient type from a lambda copy is not a member of the nest host (its non-transient original is/will be)
 		this.binding.setNestHost(nestHost);
-		nestHost.addNestMember(this.binding);
+		if (concreteType)
+			nestHost.addNestMember(this.binding);
 	}
 }
 

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/LambdaExpressionsTest.java

@@ -26,6 +26,7 @@
 import org.eclipse.jdt.core.tests.compiler.regression.AbstractRegressionTest.JavacTestOptions.EclipseJustification;
 import org.eclipse.jdt.core.tests.compiler.regression.AbstractRegressionTest.JavacTestOptions.JavacHasABug;
 import org.eclipse.jdt.core.tests.util.Util;
+import org.eclipse.jdt.core.util.ClassFileBytesDisassembler;
 import org.eclipse.jdt.core.util.IAttributeNamesConstants;
 import org.eclipse.jdt.core.util.IClassFileAttribute;
 import org.eclipse.jdt.core.util.IClassFileReader;
@@ -8903,6 +8904,54 @@ public static void main(String [] args) {
 	  },
 	  "Callable");
 }
+// https://github.com/eclipse-jdt/eclipse.jdt.core/issues/4204
+// negative testing that the synthetic method - access - not present in the class declaring the private method accessed by a nestmate
+public void testIssue4204() throws Exception {
+
+	this.runConformTest(
+			new String[] {
+					"X.java",
+					"""
+					interface Base {
+						Base get(int x);
+					}
+					public class X {
+						private void privateMethod(int p) {
+							System.out.println("Private method called with " + p);
+						}
+					    <T> Base foo(Base b) {
+					        return b;
+					     }
+					    void bar(Base b) {
+					    	b.get(42);
+					    }
+					    void testCase() {
+					        bar(foo((int p)-> {
+					        	new Object() {
+					        		void foo() {
+					        			privateMethod(p);
+					        		}
+					        	}.foo();
+					        	return null;}
+					        ));
+					     }
+
+					    public static void main(String[] args) {
+							new X().testCase();
+						}
+					}
+					""",
+			},
+			"Private method called with 42");
+
+	if (this.complianceLevel >= ClassFileConstants.JDK11) {
+		String unExpectedPartialOutput = "access$";
+		verifyNegativeClassFile(unExpectedPartialOutput, "X.class", ClassFileBytesDisassembler.SYSTEM);
+	} else {
+		String expectedPartialOutput = "static synthetic void access$0(X arg0, int arg1);";
+		verifyClassFile(expectedPartialOutput, "X.class", ClassFileBytesDisassembler.SYSTEM);
+	}
+}
 public static Class testClass() {
 	return LambdaExpressionsTest.class;
 }