Reproduce IllegalAccessorError from repackaging+class merging

Bug: b/516829757
Change-Id: I58a06c6debf86fd16fab0b1905aeee4b511e971e

src/test/java/com/android/tools/r8/classmerging/horizontal/InstanceFieldMergingWithPackagePrivateFieldTypeTest.java

diff --git a/src/test/java/com/android/tools/r8/classmerging/horizontal/InstanceFieldMergingWithPackagePrivateFieldTypeTest.java b/src/test/java/com/android/tools/r8/classmerging/horizontal/InstanceFieldMergingWithPackagePrivateFieldTypeTest.java
new file mode 100644
index 0000000..5fc7827
--- /dev/null
+++ b/src/test/java/com/android/tools/r8/classmerging/horizontal/InstanceFieldMergingWithPackagePrivateFieldTypeTest.java
@@ -0,0 +1,104 @@
+// Copyright (c) 2026, the R8 project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+package com.android.tools.r8.classmerging.horizontal;
+
+import com.android.tools.r8.NeverClassInline;
+import com.android.tools.r8.NeverInline;
+import com.android.tools.r8.NoHorizontalClassMerging;
+import com.android.tools.r8.TestParameters;
+import com.android.tools.r8.references.Reference;
+import org.junit.Test;
+
+public class InstanceFieldMergingWithPackagePrivateFieldTypeTest
+    extends HorizontalClassMergingTestBase {
+
+  public InstanceFieldMergingWithPackagePrivateFieldTypeTest(TestParameters parameters) {
+    super(parameters);
+  }
+
+  @Test
+  public void testR8() throws Exception {
+    testForR8(parameters)
+        .addInnerClasses(getClass())
+        .addKeepMainRule(Main.class)
+        .addKeepClassAndMembersRules(PublicClass.class, PackagePrivateClass.class)
+        .addHorizontallyMergedClassesInspector(
+            inspector ->
+                inspector.assertIsCompleteMergeGroup(A.class, B.class).assertNoOtherClassesMerged())
+        .addRepackagingInspector(
+            inspector -> inspector.assertIsRepackaged(Reference.classFromClass(Consumer.class)))
+        .enableInliningAnnotations()
+        .enableNeverClassInliningAnnotations()
+        .enableNoHorizontalClassMergingAnnotations()
+        .setMinApi(parameters)
+        .compile()
+        .run(parameters.getRuntime(), Main.class)
+        .assertFailureWithErrorThatThrows(IllegalAccessError.class);
+  }
+
+  static class Main {
+
+    public static void main(String[] args) {
+      A a = new A(new PackagePrivateClass());
+      B b = new B(new Object());
+      Consumer.accept(a, b);
+      A.disableRepackaging();
+      B.disableRepackaging();
+    }
+  }
+
+  // Repackaged to another package.
+  @NoHorizontalClassMerging
+  public static class Consumer {
+
+    @NeverInline
+    public static void accept(A a, B b) {
+      PublicClass publicClass = a.f;
+      publicClass.doSomething();
+      System.out.println(b.f);
+    }
+  }
+
+  @NeverClassInline
+  public static class A {
+
+    public PackagePrivateClass f;
+
+    public A(PackagePrivateClass f) {
+      this.f = f;
+    }
+
+    @NeverInline
+    public static void disableRepackaging() {
+      System.out.println(Main.class); // Access package-private class.
+    }
+  }
+
+  @NeverClassInline
+  public static class B {
+
+    public Object f;
+
+    public B(Object f) {
+      this.f = f;
+    }
+
+    @NeverInline
+    public static void disableRepackaging() {
+      System.out.println(Main.class); // Access package-private class.
+    }
+  }
+
+  // Kept.
+  public static class PublicClass {
+
+    @NeverInline
+    public void doSomething() {
+      System.out.println("PublicClass!");
+    }
+  }
+
+  // Kept.
+  static class PackagePrivateClass extends PublicClass {}
+}

src/test/testbase/java/com/android/tools/r8/utils/codeinspector/RepackagingInspector.java

diff --git a/src/test/testbase/java/com/android/tools/r8/utils/codeinspector/RepackagingInspector.java b/src/test/testbase/java/com/android/tools/r8/utils/codeinspector/RepackagingInspector.java
index 7804ab1..3de5ec1 100644
--- a/src/test/testbase/java/com/android/tools/r8/utils/codeinspector/RepackagingInspector.java
+++ b/src/test/testbase/java/com/android/tools/r8/utils/codeinspector/RepackagingInspector.java
@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 package com.android.tools.r8.utils.codeinspector;
 
+import static org.junit.Assert.assertNotEquals;
+
 import com.android.tools.r8.graph.DexItemFactory;
 import com.android.tools.r8.graph.DexType;
 import com.android.tools.r8.references.ClassReference;
@@ -19,6 +21,11 @@
     this.repackagingLens = repackagingLens;
   }
 
+  public RepackagingInspector assertIsRepackaged(ClassReference classReference) {
+    assertNotEquals(classReference, getTarget(classReference));
+    return this;
+  }
+
   public ClassReference getSource(ClassReference classReference) {
     return getSource(ClassReferenceUtils.toDexType(classReference, dexItemFactory));
   }