Provide invalid class name in exception message

See gh-31612

spring-core/src/main/java/org/springframework/aot/generate/GeneratedFiles.java

@@ -161,7 +161,7 @@ public interface GeneratedFiles {
 
 	private static String getClassNamePath(String className) {
 		Assert.hasLength(className, "'className' must not be empty");
-		Assert.isTrue(isJavaIdentifier(className), "'className' must be a valid identifier");
+		Assert.isTrue(isJavaIdentifier(className), "'className' " + className + " must be a valid identifier");
 		return ClassUtils.convertClassNameToResourcePath(className) + ".java";
 	}
 

spring-core/src/test/java/org/springframework/aot/generate/GeneratedFilesTests.java

@@ -78,7 +78,7 @@ class GeneratedFilesTests {
 		assertThatIllegalArgumentException()
 				.isThrownBy(() -> this.generatedFiles
 						.addSourceFile("com/example/HelloWorld.java", "{}"))
-				.withMessage("'className' must be a valid identifier");
+				.withMessage("'className' com/example/HelloWorld.java must be a valid identifier");
 	}
 
 	@Test