Ensure classloader compatibility when generating dynamic subclass

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fix `ClassFormatError` when attempting to create a dynamic subclass for a class that has no package. ([Issue 638](https://github.com/jqno/equalsverifier/issues/638))
+- Fix `LinkageError` when running Quarkus dev mode and testing an abstract class. ([Issue 550](https://github.com/jqno/equalsverifier/issues/550))
 
 ## [3.12] - 2022-11-30
 

equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/Instantiator.java

@@ -93,12 +93,16 @@ public static synchronized <S> Class<S> giveDynamicSubclass(
             "$" +
             nameSuffix;
 
-        Class<S> existsAlready = (Class<S>) classForName(name);
+        Class<?> context = isSystemClass ? Instantiator.class : superclass;
+        ClassLoader classLoader = context.getClassLoader();
+
+        // `mvn quarkus:dev` does strange classloader stuff. We need to make sure that we
+        // check existence with the correct classloader. I don't know how to unit test this.
+        Class<S> existsAlready = (Class<S>) classForName(classLoader, name);
         if (existsAlready != null) {
             return existsAlready;
         }
 
-        Class<?> context = isSystemClass ? Instantiator.class : superclass;
         ClassLoadingStrategy<ClassLoader> cs = getClassLoadingStrategy(context);
         DynamicType.Builder<S> builder = new ByteBuddy()
             .with(TypeValidation.DISABLED)
@@ -107,7 +111,7 @@ public static synchronized <S> Class<S> giveDynamicSubclass(
 
         builder = modify.apply(builder);
 
-        return (Class<S>) builder.make().load(context.getClassLoader(), cs).getLoaded();
+        return (Class<S>) builder.make().load(classLoader, cs).getLoaded();
     }
 
     private static String getPackageName(Class<?> type) {

equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/Util.java

@@ -27,6 +27,24 @@ public static <T> Class<T> classForName(String className) {
         }
     }
 
+    /**
+     * Helper method to resolve a Class of a given name through a given ClassLoader.
+     *
+     * @param classLoader The class loader to resolve the class against.
+     * @param className The fully qualified name of the class to resolve.
+     * @param <T> The type of the class to resolve.
+     * @return The corresponding class if it exists, null otherwise.
+     */
+    @SuppressWarnings("unchecked")
+    public static <T> Class<T> classForName(ClassLoader classLoader, String className) {
+        try {
+            return (Class<T>) classLoader.loadClass(className);
+        } catch (ClassNotFoundException | VerifyError e) {
+            // Catching VerifyError fixes issue #147. I don't know how to unit test it.
+            return null;
+        }
+    }
+
     /**
      * Helper method to create an array of Classes.
      *

equalsverifier-core/src/test/java/nl/jqno/equalsverifier/internal/reflection/UtilTest.java

@@ -29,6 +29,20 @@ public void forNameReturnsNull_whenTypeDoesntExist() {
         assertNull(actual);
     }
 
+    @Test
+    public void forNameWithClassLoaderReturnsClass_whenTypeExists() {
+        ClassLoader cl = getClass().getClassLoader();
+        Class<?> actual = Util.classForName(cl, "java.util.GregorianCalendar");
+        assertEquals(actual, GregorianCalendar.class);
+    }
+
+    @Test
+    public void forNameWithClassLoaderReturnsNull_whenTypeDoesntExist() {
+        ClassLoader cl = getClass().getClassLoader();
+        Class<?> actual = Util.classForName(cl, "this.type.does.not.exist");
+        assertNull(actual);
+    }
+
     @Test
     public void classesReturnsItsArguments() {
         Class<?>[] expected = new Class<?>[] { String.class, Object.class };