chore: Pre-DIREGAPIC Refactoring googleapis#1

 This is as minimal of a PR that I could make stuch that:
 1) It compiles and tests run single composer plus minimal
 2) All the key changes are present (abstract/grpc class, comment composer, class names, golden files move)

 I had to add a few quite ugly and artificial   constructs:
 fake `ClassComposer` under `composer` package which simply extends `composer.common.Composer` to void changing the rest of the classes
 put back static methods in `ClassNames` and `StubCommentComposer` and `TestProtoLoaderUtil` (for the same reasons as above). All of those chagnes are marked with `// TODO: remove after Pre-DIREGAPIC refactoring is fully merged` statement.

Author: vam-google

src/main/java/com/google/api/generator/gapic/composer/BUILD.bazel

@@ -18,7 +18,9 @@ java_library(
         "//src/main/java/com/google/api/generator/engine/writer",
         "//src/main/java/com/google/api/generator/gapic:status_java_proto",
         "//src/main/java/com/google/api/generator/gapic/composer/comment",
+        "//src/main/java/com/google/api/generator/gapic/composer/common",
         "//src/main/java/com/google/api/generator/gapic/composer/defaultvalue",
+        "//src/main/java/com/google/api/generator/gapic/composer/grpc",
         "//src/main/java/com/google/api/generator/gapic/composer/resourcename",
         "//src/main/java/com/google/api/generator/gapic/composer/samplecode",
         "//src/main/java/com/google/api/generator/gapic/composer/store",

src/main/java/com/google/api/generator/gapic/composer/ClassComposer.java

@@ -14,10 +14,5 @@
 
 package com.google.api.generator.gapic.composer;
 
-import com.google.api.generator.gapic.model.GapicClass;
-import com.google.api.generator.gapic.model.GapicContext;
-import com.google.api.generator.gapic.model.Service;
-
-public interface ClassComposer {
-  GapicClass generate(GapicContext context, Service serivce);
-}
+public interface ClassComposer
+    extends com.google.api.generator.gapic.composer.common.ClassComposer {}

src/main/java/com/google/api/generator/gapic/composer/Composer.java

@@ -17,6 +17,7 @@
 import com.google.api.generator.engine.ast.ClassDefinition;
 import com.google.api.generator.engine.ast.ScopeNode;
 import com.google.api.generator.gapic.composer.comment.CommentComposer;
+import com.google.api.generator.gapic.composer.grpc.ServiceSettingsClassComposer;
 import com.google.api.generator.gapic.composer.resourcename.ResourceNameHelperClassComposer;
 import com.google.api.generator.gapic.model.GapicClass;
 import com.google.api.generator.gapic.model.GapicClass.Kind;

src/main/java/com/google/api/generator/gapic/composer/ServiceStubSettingsClassComposer.java

@@ -985,7 +985,7 @@ private static List<MethodDefinition> createDefaultHelperAndGetterMethods(
     javaMethods.add(
         MethodDefinition.builder()
             .setHeaderCommentStatements(
-                SettingsCommentComposer.DEFAULT_GRPC_TRANSPORT_PROVIDER_BUILDER_METHOD_COMMENT)
+                SettingsCommentComposer.DEFAULT_TRANSPORT_PROVIDER_BUILDER_METHOD_COMMENT)
             .setScope(ScopeNode.PUBLIC)
             .setIsStatic(true)
             .setReturnType(returnType)

src/main/java/com/google/api/generator/gapic/composer/comment/SettingsCommentComposer.java

@@ -67,7 +67,7 @@ public class SettingsCommentComposer {
   public static final CommentStatement DEFAULT_CREDENTIALS_PROVIDER_BUILDER_METHOD_COMMENT =
       toSimpleComment("Returns a builder for the default credentials for this service.");
 
-  public static final CommentStatement DEFAULT_GRPC_TRANSPORT_PROVIDER_BUILDER_METHOD_COMMENT =
+  public static final CommentStatement DEFAULT_TRANSPORT_PROVIDER_BUILDER_METHOD_COMMENT =
       toSimpleComment("Returns a builder for the default ChannelProvider for this service.");
 
   public static final CommentStatement NEW_BUILDER_METHOD_COMMENT =

src/main/java/com/google/api/generator/gapic/composer/comment/StubCommentComposer.java

@@ -22,44 +22,69 @@
 public class StubCommentComposer {
   private static final String STUB_CLASS_HEADER_SUMMARY_PATTERN =
       "Base stub class for the %s service API.";
-  private static final String GRPC_CALLABLE_FACTORY_CLASS_HEADER_SUMMARY_PATTERN =
-      "gRPC callable factory implementation for the %s service API.";
-  private static final String GRPC_STUB_CLASS_HEADER_SUMMARY_PATTERN =
-      "gRPC stub implementation for the %s service API.";
+  private static final String TRANSPORT_CALLABLE_FACTORY_CLASS_HEADER_SUMMARY_PATTERN =
+      "%s callable factory implementation for the %s service API.";
+  private static final String TRANSPORT_STUB_CLASS_HEADER_SUMMARY_PATTERN =
+      "%s stub implementation for the %s service API.";
 
   private static final String ADVANCED_USAGE_DESCRIPTION = "This class is for advanced usage.";
   private static final String ADVANCED_USAGE_API_REFLECTION_DESCRIPTION =
       "This class is for advanced usage and reflects the underlying API directly.";
 
+  // TODO: remove after Pre-DIREGAPIC refactoring is fully merged
+  private static final StubCommentComposer GRPC_INSTANCE = new StubCommentComposer("gRPC");
+
+  private final String transportPrefix;
+
+  public StubCommentComposer(String transportPrefix) {
+    this.transportPrefix = transportPrefix;
+  }
+
+  // TODO: remove after Pre-DIREGAPIC refactoring is fully merged
   public static List<CommentStatement> createGrpcServiceStubClassHeaderComments(
       String serviceName, boolean isDeprecated) {
+    return GRPC_INSTANCE.createTransportServiceStubClassHeaderComments(serviceName, isDeprecated);
+  }
+
+  public List<CommentStatement> createTransportServiceStubClassHeaderComments(
+      String serviceName, boolean isDeprecated) {
     JavaDocComment.Builder javaDocBuilder = JavaDocComment.builder();
     if (isDeprecated) {
       javaDocBuilder = javaDocBuilder.setDeprecated(CommentComposer.DEPRECATED_CLASS_STRING);
     }
-
     return Arrays.asList(
         CommentComposer.AUTO_GENERATED_CLASS_COMMENT,
         CommentStatement.withComment(
             javaDocBuilder
-                .addComment(String.format(GRPC_STUB_CLASS_HEADER_SUMMARY_PATTERN, serviceName))
+                .addComment(
+                    String.format(
+                        TRANSPORT_STUB_CLASS_HEADER_SUMMARY_PATTERN, transportPrefix, serviceName))
                 .addParagraph(ADVANCED_USAGE_API_REFLECTION_DESCRIPTION)
                 .build()));
   }
 
+  // TODO: remove after Pre-DIREGAPIC refactoring is fully merged
   public static List<CommentStatement> createGrpcServiceCallableFactoryClassHeaderComments(
       String serviceName, boolean isDeprecated) {
+    return GRPC_INSTANCE.createTransportServiceCallableFactoryClassHeaderComments(
+        serviceName, isDeprecated);
+  }
+
+  public List<CommentStatement> createTransportServiceCallableFactoryClassHeaderComments(
+      String serviceName, boolean isDeprecated) {
     JavaDocComment.Builder javaDocBuilder = JavaDocComment.builder();
     if (isDeprecated) {
       javaDocBuilder = javaDocBuilder.setDeprecated(CommentComposer.DEPRECATED_CLASS_STRING);
     }
-
     return Arrays.asList(
         CommentComposer.AUTO_GENERATED_CLASS_COMMENT,
         CommentStatement.withComment(
             javaDocBuilder
                 .addComment(
-                    String.format(GRPC_CALLABLE_FACTORY_CLASS_HEADER_SUMMARY_PATTERN, serviceName))
+                    String.format(
+                        TRANSPORT_CALLABLE_FACTORY_CLASS_HEADER_SUMMARY_PATTERN,
+                        transportPrefix,
+                        serviceName))
                 .addParagraph(ADVANCED_USAGE_DESCRIPTION)
                 .build()));
   }