Fix JPA setup in Nomulus tool (#780)

* Fix JPA setup in Nomulus tool

Hibernate unnecessarily scans third-party classes in the Nomulus tool,
hitting a bug and fails to set up.

In this change we properly configured persistence.xml to include the orm mapping file (orm.xml) and disable 
auto detection, and provided a custom (NOOP) scanner
to work around Hibernate scanner bugs.

Also improved on the :core:registryIntegrationTest task to test for
JPA setup as well as dependency-packaging.

core/src/main/java/google/registry/persistence/NoopJpaEntityScanner.java

@@ -0,0 +1,45 @@
+// Copyright 2020 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.persistence;
+
+import com.google.common.collect.ImmutableSet;
+import org.hibernate.boot.archive.internal.StandardArchiveDescriptorFactory;
+import org.hibernate.boot.archive.scan.internal.ScanResultImpl;
+import org.hibernate.boot.archive.scan.internal.StandardScanner;
+import org.hibernate.boot.archive.scan.spi.ScanEnvironment;
+import org.hibernate.boot.archive.scan.spi.ScanOptions;
+import org.hibernate.boot.archive.scan.spi.ScanParameters;
+import org.hibernate.boot.archive.scan.spi.ScanResult;
+import org.hibernate.boot.archive.scan.spi.Scanner;
+
+/**
+ * A do-nothing {@link Scanner} for Hibernate that works around bugs in Hibernate's default
+ * implementation. This is required for the Nomulus tool.
+ *
+ * <p>Please refer to <a href="../../../../resources/META-INF/persistence.xml">persistence.xml</a>
+ * for more information.
+ */
+public class NoopJpaEntityScanner extends StandardScanner {
+
+  public NoopJpaEntityScanner() {
+    super(StandardArchiveDescriptorFactory.INSTANCE);
+  }
+
+  @Override
+  public ScanResult scan(
+      ScanEnvironment environment, ScanOptions options, ScanParameters parameters) {
+    return new ScanResultImpl(ImmutableSet.of(), ImmutableSet.of(), ImmutableSet.of());
+  }
+}

core/src/main/java/google/registry/tools/RegistryCli.java

@@ -112,8 +112,6 @@ final class RegistryCli implements AutoCloseable, CommandRunner {
     // Create all command instances. It would be preferrable to do this in the constructor, but
     // JCommander mutates the command instances and doesn't reset them so we have to do it for every
     // run.
-    // TODO(weiminyu): extract this into a standalone static method to simplify
-    //   :core:registryToolIntegrationTest
     try {
       for (Map.Entry<String, ? extends Class<? extends Command>> entry : commands.entrySet()) {
         Command command = entry.getValue().getDeclaredConstructor().newInstance();

core/src/main/resources/META-INF/persistence.xml

@@ -11,14 +11,33 @@
     <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
 
     <!--
-      All JPA entities must be enumerated here. JPA does not support auto detection.
+      All JPA entity-mapping files and annotated classes must be enumerated
+      here. Automatic entity detection is not part of the JPA spec. Explicit
+      declaration makes it easier to migrate to another provider.
 
-      Note that Hibernate's auto detection functionality (hibernate.archive.autodection)
-      does not meet our needs. It only scans archives, not the 'classes' folders. So we
-      are left with two options:
-      *  Move tests to another (sub)project. This is not a big problem, but feels unnatural.
-      *  Use Hibernate's ServiceRegistry for bootstrapping (not JPA-compliant)
+      Although Hibernate provides the auto detection functionality (configured by
+      the hibernate.archive.autodetection property), it relies on a fragile
+      scanner that can be broken by certain classes. For example, in the uber jar
+      for the Nomulus tool, a repackaged Guava class ( {@code
+      com.google.appengine.repackaged.com.google.common.html.LinkDetector})
+      from appengine-api-1.0-sdk:1.9.81 can break the scanner in
+      hibernate-core:5.4.17.Final. The large number of third-party classes also
+      makes JPA setup noticeably slower in the tool.
+
+      When auto detection is enabled in Hibernate, we also need a separate
+      persistence.xml for tests. See <a
+      href="https://stackoverflow.com/questions/61127082/hibernate-doesnt-find-entities-in-test">
+      this webpage</a> for an example.
+
+      Because of the reasons above, we disable auto detection in Hibernate.
+
+      When auto detection is disabled, Hibernate still invokes the scanner which always
+      goes over the archive that has this file. We need to override the default scanner
+      with an NOOP one for Nomulus tool.
     -->
+
+    <mapping-file>META-INF/orm.xml</mapping-file>
+
     <class>google.registry.model.billing.BillingEvent$Cancellation</class>
     <class>google.registry.model.billing.BillingEvent$OneTime</class>
     <class>google.registry.model.billing.BillingEvent$Recurring</class>
@@ -82,5 +101,12 @@
 
     <!-- TODO(weiminyu): check out application-layer validation. -->
     <validation-mode>NONE</validation-mode>
+    <properties>
+      <!-- Disables auto detection. -->
+      <property name="hibernate.archive.autodetection" value=""/>
+      <!-- NOOP scanner needed for Nomulus tool. -->
+      <property name="hibernate.archive.scanner"
+          value="google.registry.persistence.NoopJpaEntityScanner"/>
+    </properties>
   </persistence-unit>
 </persistence>