fix: Generator to skip generation for empty services. (#3051)

fixes #2750
Skip parsing a service if no RPCs found for. 
In the scenario that only one service with no RPCs or all services have
no RPCs, falls back to #2460

This pr also reverts a change brought by #985, and removes the relevant
tests. For more context, this has been discussed
[here](#2750 (comment)).

---------

Co-authored-by: Lawrence Qiu <lawrenceqiu@google.com>

Author: zhumin8

gapic-generator-java/src/main/java/com/google/api/generator/gapic/composer/samplecode/ServiceClientHeaderSampleComposer.java

@@ -52,10 +52,6 @@ public static Sample composeClassHeaderSample(
       TypeNode clientType,
       Map<String, ResourceName> resourceNames,
       Map<String, Message> messageTypes) {
-    if (service.methods().isEmpty()) {
-      return ServiceClientMethodSampleComposer.composeEmptyServiceSample(clientType, service);
-    }
-
     // Use the first pure unary RPC method's sample code as showcase, if no such method exists, use
     // the first method in the service's methods list.
     Method method =

gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java

@@ -435,6 +435,17 @@ public static List<Service> parseService(
       Transport transport) {
 
     return fileDescriptor.getServices().stream()
+        .filter(
+            serviceDescriptor -> {
+              List<MethodDescriptor> methodsList = serviceDescriptor.getMethods();
+              if (methodsList.isEmpty()) {
+                LOGGER.warning(
+                    String.format(
+                        "Service %s has no RPC methods and will not be generated",
+                        serviceDescriptor.getName()));
+              }
+              return !methodsList.isEmpty();
+            })
         .map(
             s -> {
               // Workaround for a missing default_host and oauth_scopes annotation from a service

gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpcrest/ServiceClientClassComposerTest.java

@@ -40,20 +40,6 @@ void generateServiceClasses() {
     Assert.assertCodeEquals(goldenFilePath, visitor.write());
   }
 
-  @Test
-  void generateServiceClassesEmpty() {
-    GapicContext context = GrpcRestTestProtoLoader.instance().parseShowcaseEcho();
-    Service echoProtoService = context.services().get(1);
-    GapicClass clazz = ServiceClientClassComposer.instance().generate(context, echoProtoService);
-
-    JavaWriterVisitor visitor = new JavaWriterVisitor();
-    clazz.classDefinition().accept(visitor);
-    GoldenFileWriter.saveCodegenToFile(this.getClass(), "EchoEmpty.golden", visitor.write());
-    Path goldenFilePath =
-        Paths.get(GoldenFileWriter.getGoldenDir(this.getClass()), "EchoEmpty.golden");
-    Assert.assertCodeEquals(goldenFilePath, visitor.write());
-  }
-
   @Test
   void generateServiceClassesWicked() {
     GapicContext context = GrpcRestTestProtoLoader.instance().parseShowcaseWicked();

gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpcrest/goldens/EchoEmpty.golden

@@ -692,6 +692,19 @@ void testServiceWithoutApiVersionParsed() {
     assertNull(parsedBookshopService.apiVersion());
   }
 
+  @Test
+  void parseServiceWithNoMethodsTest() {
+    FileDescriptor fileDescriptor =
+        com.google.api.service.without.methods.test.ServiceWithNoMethodsOuterClass.getDescriptor();
+    Map<String, Message> messageTypes = Parser.parseMessages(fileDescriptor);
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(fileDescriptor);
+    List<com.google.api.generator.gapic.model.Service> services =
+        Parser.parseService(
+            fileDescriptor, messageTypes, resourceNames, Optional.empty(), new HashSet<>());
+    assertEquals(1, services.size());
+    assertEquals("EchoWithMethods", services.get(0).overriddenName());
+  }
+
   private void assertMethodArgumentEquals(
       String name, TypeNode type, List<TypeNode> nestedFields, MethodArgument argument) {
     assertEquals(name, argument.name());

gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/ParserTest.java

@@ -163,11 +163,6 @@ service Echo {
   }
 }
 
-// Generator should not fail when encounter a service without methods
-service EchoEmpy {
-  option (google.api.default_host) = "localhost:7469";
-}
-
 // A severity enum used to test enum capabilities in GAPIC surfaces
 enum Severity {
   UNNECESSARY = 0;

gapic-generator-java/src/test/proto/echo_grpcrest.proto

@@ -0,0 +1,131 @@
+// Copyright 2018 Google LLC
+//
+// 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
+//
+//     https://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.
+
+syntax = "proto3";
+
+import "google/api/annotations.proto";
+import "google/api/client.proto";
+import "google/api/field_behavior.proto";
+import "google/api/field_info.proto";
+import "google/api/resource.proto";
+import "google/longrunning/operations.proto";
+import "google/protobuf/duration.proto";
+import "google/protobuf/timestamp.proto";
+import "google/rpc/status.proto";
+
+package google.api.service.without.methods.test.v1;
+
+option java_package = "com.google.api.service.without.methods.test";
+option java_multiple_files = true;
+option java_outer_classname = "ServiceWithNoMethodsOuterClass";
+
+option (google.api.resource_definition) = {
+  type: "showcase.googleapis.com/AnythingGoes"
+  pattern: "*"
+};
+// This proto is used to test scenarios where a service does not have any rpc methods
+
+// This service is used as control group when it is not empty.
+service EchoWithMethods {
+  // This service is meant to only run locally on the port 7469 (keypad digits
+  // for "show").
+  option (google.api.default_host) = "localhost:7469";
+  option (google.api.oauth_scopes) =
+      "https://www.googleapis.com/auth/cloud-platform";
+
+  // This method simply echos the request. This method is showcases unary rpcs.
+  rpc EchoWithMethod(EchoRequest) returns (EchoResponse) {
+    option (google.api.http) = {
+      post: "/v1beta1/echo:echo"
+      body: "*"
+    };
+    option (google.api.method_signature) = "content";
+    option (google.api.method_signature) = "error";
+    option (google.api.method_signature) = "content,severity";
+    option (google.api.method_signature) = "name";
+    option (google.api.method_signature) = "parent";
+    option (google.api.method_signature) = "";
+  }
+}
+
+// This service is to test when no method specified.
+service EchoWithoutMethods {
+  // This service is meant to only run locally on the port 7469 (keypad digits
+  // for "show").
+  option (google.api.default_host) = "localhost:7469";
+  option (google.api.oauth_scopes) =
+    "https://www.googleapis.com/auth/cloud-platform";
+}
+
+// A severity enum used to test enum capabilities in GAPIC surfaces
+enum Severity {
+  UNNECESSARY = 0;
+  NECESSARY = 1;
+  URGENT = 2;
+  CRITICAL = 3;
+}
+
+message Foobar {
+  option (google.api.resource) = {
+    type: "showcase.googleapis.com/Foobar"
+    pattern: "projects/{project}/foobars/{foobar}"
+    pattern: "projects/{project}/chocolate/variants/{variant}/foobars/{foobar}"
+    pattern: "foobars/{foobar}"
+    pattern: "bar_foos/{bar_foo}/foobars/{foobar}"
+    pattern: "*"
+  };
+
+  string name = 1;
+  string info = 2;
+}
+
+// The request message used for the Echo, Collect and Chat methods.
+// If content or opt are set in this message then the request will succeed.
+// If status is set in this message
+// then the status will be returned as an error.
+message EchoRequest {
+  string name = 5 [
+    (google.api.resource_reference).type = "showcase.googleapis.com/Foobar",
+    (google.api.field_behavior) = REQUIRED
+  ];
+
+  string parent = 6 [
+    (google.api.resource_reference).child_type =
+        "showcase.googleapis.com/AnythingGoes",
+    (google.api.field_behavior) = REQUIRED
+  ];
+
+  oneof response {
+    // The content to be echoed by the server.
+    string content = 1;
+
+    // The error to be thrown by the server.
+    google.rpc.Status error = 2;
+  }
+
+  // The severity to be echoed by the server.
+  Severity severity = 3;
+
+  Foobar foobar = 4;
+}
+
+// The response message for the Echo methods.
+message EchoResponse {
+  // The content specified in the request.
+  string content = 1;
+
+  // The severity specified in the request.
+  Severity severity = 2;
+}
+

gapic-generator-java/src/test/proto/service_with_no_methods.proto

@@ -440,6 +440,24 @@
     "allDeclaredClasses": true,
     "allPublicClasses": true
   },
+  {
+    "name": "com.google.api.TypeReference",
+    "queryAllDeclaredConstructors": true,
+    "queryAllPublicConstructors": true,
+    "queryAllDeclaredMethods": true,
+    "allPublicMethods": true,
+    "allDeclaredClasses": true,
+    "allPublicClasses": true
+  },
+  {
+    "name": "com.google.api.TypeReference$Builder",
+    "queryAllDeclaredConstructors": true,
+    "queryAllPublicConstructors": true,
+    "queryAllDeclaredMethods": true,
+    "allPublicMethods": true,
+    "allDeclaredClasses": true,
+    "allPublicClasses": true
+  },
   {
     "name": "com.google.cloud.location.GetLocationRequest",
     "queryAllDeclaredConstructors": true,