Improve error message for missing datasource at build time with an implicit persistence unit

Author: yrodiere

extensions/hibernate-orm/deployment/src/main/java/io/quarkus/hibernate/orm/deployment/HibernateOrmProcessor.java

@@ -914,8 +914,15 @@ private void handleHibernateORMWithNoPersistenceXml(
                 && !defaultJdbcDataSource.isPresent()) {
             String persistenceUnitName = PersistenceUnitUtil.DEFAULT_PERSISTENCE_UNIT_NAME;
             String dataSourceName = DataSourceUtil.DEFAULT_DATASOURCE_NAME;
-            throw PersistenceUnitUtil.unableToFindDataSource(persistenceUnitName, dataSourceName,
-                    DataSourceUtil.dataSourceNotConfigured(dataSourceName));
+            var cause = DataSourceUtil.dataSourceNotConfigured(dataSourceName);
+            throw new ConfigurationException(String.format(Locale.ROOT,
+                    "Persistence unit '%s' defines entities %s, but its datasource '%s' cannot be found: %s"
+                            + " Alternatively, disable Hibernate ORM by setting '%s=false', and the entities will be ignored.",
+                    persistenceUnitName, modelClassesAndPackagesForDefaultPersistenceUnit,
+                    dataSourceName,
+                    cause.getMessage(),
+                    HibernateOrmRuntimeConfig.extensionPropertyKey("enabled")),
+                    cause);
         }
 
         for (Entry<String, HibernateOrmConfigPersistenceUnit> persistenceUnitEntry : hibernateOrmConfig.namedPersistenceUnits()

extensions/hibernate-orm/deployment/src/test/java/io/quarkus/hibernate/orm/config/NoDatasourceTest.java

@@ -20,10 +20,12 @@ public class NoDatasourceTest {
             .overrideConfigKey("quarkus.datasource.jdbc", "false")
             .assertException(t -> assertThat(t)
                     .hasMessageContainingAll(
-                            "Unable to find datasource '<default>' for persistence unit '<default>'",
+                            "Persistence unit '<default>' defines entities [" + MyEntity.class.getName()
+                                    + "], but its datasource '<default>' cannot be found",
                             "Datasource '<default>' is not configured.",
                             "To solve this, configure datasource '<default>'",
-                            "Refer to https://quarkus.io/guides/datasource for guidance."));
+                            "Refer to https://quarkus.io/guides/datasource for guidance.",
+                            "Alternatively, disable Hibernate ORM by setting 'quarkus.hibernate-orm.enabled=false', and the entities will be ignored"));
 
     @Test
     public void test() {