feat(gapic-generator-java): Cause a noop when no services are found

Author: diegomarquezp

gapic-generator-java/src/main/java/com/google/api/generator/Main.java

@@ -15,6 +15,7 @@
 package com.google.api.generator;
 
 import com.google.api.generator.gapic.Generator;
+import com.google.api.generator.gapic.protoparser.NoServicesFoundException;
 import com.google.protobuf.ExtensionRegistry;
 import com.google.protobuf.compiler.PluginProtos.CodeGeneratorRequest;
 import com.google.protobuf.compiler.PluginProtos.CodeGeneratorResponse;
@@ -25,7 +26,12 @@ public static void main(String[] args) throws IOException {
     ExtensionRegistry registry = ExtensionRegistry.newInstance();
     ProtoRegistry.registerAllExtensions(registry);
     CodeGeneratorRequest request = CodeGeneratorRequest.parseFrom(System.in, registry);
-    CodeGeneratorResponse response = Generator.generateGapic(request);
-    response.writeTo(System.out);
+    try {
+      CodeGeneratorResponse response = Generator.generateGapic(request);
+      response.writeTo(System.out);
+    } catch (NoServicesFoundException ex) {
+      // If no services are found in the protos we will no-op
+      System.err.println("No services found to generate");
+    }
   }
 }

gapic-generator-java/src/main/java/com/google/api/generator/gapic/Generator.java

@@ -14,19 +14,22 @@
 
 package com.google.api.generator.gapic;
 
+import com.google.api.gax.rpc.StatusCode.Code;
 import com.google.api.generator.gapic.composer.Composer;
 import com.google.api.generator.gapic.model.GapicClass;
 import com.google.api.generator.gapic.model.GapicContext;
 import com.google.api.generator.gapic.model.GapicPackageInfo;
 import com.google.api.generator.gapic.model.ReflectConfig;
+import com.google.api.generator.gapic.protoparser.NoServicesFoundException;
 import com.google.api.generator.gapic.protoparser.Parser;
 import com.google.api.generator.gapic.protowriter.Writer;
 import com.google.protobuf.compiler.PluginProtos.CodeGeneratorRequest;
 import com.google.protobuf.compiler.PluginProtos.CodeGeneratorResponse;
 import java.util.List;
 
 public class Generator {
-  public static CodeGeneratorResponse generateGapic(CodeGeneratorRequest request) {
+  public static CodeGeneratorResponse generateGapic(CodeGeneratorRequest request)
+      throws NoServicesFoundException {
     GapicContext context = Parser.parse(request);
     List<GapicClass> clazzes = Composer.composeServiceClasses(context);
     GapicPackageInfo packageInfo = Composer.composePackageInfo(context);

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

@@ -29,7 +29,7 @@
 import com.google.api.generator.gapic.model.GapicPackageInfo;
 import com.google.api.generator.gapic.model.Sample;
 import com.google.api.generator.gapic.model.Service;
-import com.google.common.base.Preconditions;
+import com.google.api.generator.gapic.protoparser.NoServicesFoundException;
 import com.google.common.base.Strings;
 import javax.annotation.Generated;
 
@@ -44,7 +44,9 @@ public class ClientLibraryPackageInfoComposer {
   private static final String SERVICE_DESCRIPTION_HEADER_PATTERN = "Service Description: %s";
 
   public static GapicPackageInfo generatePackageInfo(GapicContext context) {
-    Preconditions.checkState(!context.services().isEmpty(), "No services found to generate");
+    if (context.services().isEmpty()) {
+      throw new NoServicesFoundException("No services found to generate");
+    }
     // Pick some service's package, as we assume they are all the same.
     String libraryPakkage = context.services().get(0).pakkage();
 

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

@@ -0,0 +1,9 @@
+package com.google.api.generator.gapic.protoparser;
+
+public class NoServicesFoundException extends IllegalStateException {
+
+  public NoServicesFoundException() {}
+  public NoServicesFoundException(String message) {
+    super(message);
+  }
+}

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

@@ -115,7 +115,7 @@ public GapicParserException(String errorMessage) {
     }
   }
 
-  public static GapicContext parse(CodeGeneratorRequest request) {
+  public static GapicContext parse(CodeGeneratorRequest request) throws NoServicesFoundException {
     Optional<String> gapicYamlConfigPathOpt =
         PluginArgumentParser.parseGapicYamlConfigPath(request);
     Optional<List<GapicBatchingSettings>> batchingSettingsOpt =
@@ -175,7 +175,9 @@ public static GapicContext parse(CodeGeneratorRequest request) {
             mixinServices,
             transport);
 
-    Preconditions.checkState(!services.isEmpty(), "No services found to generate");
+    if (services.isEmpty()) {
+      throw new NoServicesFoundException();
+    }
 
     // TODO(vam-google): Figure out whether we should keep this allowlist or bring
     // back the unused resource names for all APIs.