proper logging and documentation for semi-deprecation of 'hibernate.dialect'

and code cleanup

Author: gavinking

hibernate-core/src/main/java/org/hibernate/cfg/AvailableSettings.java

@@ -475,6 +475,11 @@ public interface AvailableSettings {
 	 * By default, Hibernate will attempt to automatically determine the dialect from the
 	 * {@linkplain #URL JDBC URL} and JDBC metadata, so this setting is not usually necessary.
 	 *
+	 * @apiNote As of Hibernate 6, this property should not be explicitly specified,
+	 *          except when using a custom user-written implementation of {@code Dialect}.
+	 *          Instead, applications should allow Hibernate to select the {@code Dialect}
+	 *          automatically.
+	 *
 	 * @see org.hibernate.dialect.Dialect
 	 */
 	String DIALECT = "hibernate.dialect";

hibernate-core/src/main/java/org/hibernate/dialect/DB2Dialect.java

@@ -108,6 +108,9 @@
  * A {@linkplain Dialect SQL dialect} for DB2 for LUW (Linux, Unix, and Windows) version 10.5 and above.
  *
  * @author Gavin King
+ *
+ * @see DB2iDialect
+ * @see DB2zDialect
  */
 public class DB2Dialect extends Dialect {
 

hibernate-core/src/main/java/org/hibernate/engine/jdbc/dialect/internal/DialectFactoryImpl.java

@@ -84,9 +84,9 @@ public void setDialectResolver(DialectResolver dialectResolver) {
 	@Override
 	public Dialect buildDialect(Map<String,Object> configValues, DialectResolutionInfoSource resolutionInfoSource) throws HibernateException {
 		final Object dialectReference = configValues.get( AvailableSettings.DIALECT );
-		Dialect dialect = !isEmpty( dialectReference ) ?
-				constructDialect( dialectReference, resolutionInfoSource ) :
-				determineDialect( resolutionInfoSource );
+		Dialect dialect = !isEmpty( dialectReference )
+				? constructDialect( dialectReference, resolutionInfoSource )
+				: determineDialect( resolutionInfoSource );
 		logSelectedDialect( dialect );
 		return dialect;
 	}
@@ -105,6 +105,9 @@ private static void logSelectedDialect(Dialect dialect) {
 				DEPRECATION_LOGGER.deprecatedDialect( dialectClass.getSimpleName() );
 			}
 		}
+		else if ( Dialect.class.getPackage() == dialectClass.getPackage() ) {
+			DEPRECATION_LOGGER.automaticDialect( dialectClass.getSimpleName() );
+		}
 	}
 
 	@SuppressWarnings("SimplifiableIfStatement")
@@ -129,7 +132,7 @@ private Dialect constructDialect(Object dialectReference, DialectResolutionInfoS
 					(dialectClass) -> {
 						try {
 							try {
-								if (resolutionInfoSource != null) {
+								if ( resolutionInfoSource != null ) {
 									return dialectClass.getConstructor( DialectResolutionInfo.class ).newInstance(
 											resolutionInfoSource.getDialectResolutionInfo()
 									);
@@ -157,7 +160,7 @@ private Dialect constructDialect(Object dialectReference, DialectResolutionInfoS
 			final String dialectFqn = dialectReference.toString();
 			if ( LEGACY_DIALECTS.contains( dialectFqn ) ) {
 				throw new StrategySelectionException(
-						"Couldn't load the dialect class for the `hibernate.dialect` [" + dialectFqn + "], " +
+						"Couldn't load the dialect class for the 'hibernate.dialect' [" + dialectFqn + "], " +
 								"because the application is missing a dependency on the hibernate-community-dialects module. " +
 								"Hibernate 6.2 dropped support for database versions that are unsupported by vendors  " +
 								"and code for old versions was moved to the hibernate-community-dialects module. " +