feat: extract destination resource name and trace unary callables

Author: blakeli0

MODULE.bazel

@@ -0,0 +1,6 @@
+###############################################################################
+# Bazel now uses Bzlmod by default to manage external dependencies.
+# Please consider migrating your external dependencies from WORKSPACE to MODULE.bazel.
+#
+# For more details, please check https://github.com/bazelbuild/bazel/issues/18958
+###############################################################################

MODULE.bazel.lock

@@ -331,6 +331,16 @@ protected Expr createTransportSettingsInitExpr(
               .build();
     }
 
+    LambdaExpr extractor = createResourceNameExtractorClassInstance(method, messageTypes);
+    if (extractor != null) {
+      callSettingsBuilderExpr =
+          MethodInvocationExpr.builder()
+              .setExprReferenceExpr(callSettingsBuilderExpr)
+              .setMethodName("setResourceNameExtractor")
+              .setArguments(extractor)
+              .build();
+    }
+
     callSettingsBuilderExpr =
         MethodInvocationExpr.builder()
             .setExprReferenceExpr(callSettingsBuilderExpr)
@@ -1495,6 +1505,50 @@ private static Predicate<String> shouldAutoPopulate(Message methodRequestMessage
             .anyMatch(field -> field.name().equals(fieldName) && field.canBeAutoPopulated());
   }
 
+  @Nullable
+  protected static LambdaExpr createResourceNameExtractorClassInstance(
+      Method method, ImmutableMap<String, Message> messageTypes) {
+    Field resourceNameField = getDestinationResourceNameField(method, messageTypes);
+
+    if (resourceNameField == null) {
+      return null;
+    }
+
+    VariableExpr requestVarExpr = createRequestVarExpr(method);
+    List<Statement> bodyStatements = new ArrayList<>();
+    Expr returnExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(requestVarExpr)
+            .setMethodName(
+                String.format("get%s", JavaStyle.toUpperCamelCase(resourceNameField.name())))
+            .setReturnType(TypeNode.STRING)
+            .build();
+
+    return LambdaExpr.builder()
+        .setArguments(requestVarExpr.toBuilder().setIsDecl(true).build())
+        .setBody(bodyStatements)
+        .setReturnExpr(returnExpr)
+        .build();
+  }
+
+  private static Field getDestinationResourceNameField(
+      Method method, ImmutableMap<String, Message> messageTypes) {
+    if (method.inputType().reference() == null
+        || method.inputType().reference().fullName() == null) {
+      return null;
+    }
+    String methodRequestName = method.inputType().reference().fullName();
+    Message methodRequestMessage = messageTypes.get(methodRequestName);
+    if (methodRequestMessage == null) {
+      return null;
+    }
+
+    return methodRequestMessage.fields().stream()
+        .filter(f -> f.resourceReference() != null && !f.isRepeated())
+        .findFirst()
+        .orElse(null);
+  }
+
   protected LambdaExpr createRequestParamsExtractorClassInstance(
       Method method, List<Statement> classStatements) {
     List<Statement> bodyStatements = new ArrayList<>();

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

@@ -112,4 +112,14 @@ void generateGrpcServiceStubClass_bigQuery() {
     Assert.assertGoldenClass(this.getClass(), clazz, "GrpcBigQueryJobServiceStub.golden");
     Assert.assertEmptySamples(clazz.samples());
   }
+
+  @Test
+  void generateGrpcServiceStubClass_clientResourceNameExtractor() {
+    GapicContext context = GrpcTestProtoLoader.instance().parseClientResourceNameExtractorTesting();
+    Service service = context.services().get(0);
+    GapicClass clazz = GrpcServiceStubClassComposer.instance().generate(context, service);
+
+    Assert.assertGoldenClass(this.getClass(), clazz, "GrpcClientResourceNameExtractorStub.golden");
+    Assert.assertEmptySamples(clazz.samples());
+  }
 }

gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpc/GrpcServiceStubClassComposerTest.java

@@ -104,6 +104,7 @@ public class GrpcCallableNameTypeServiceStub extends CallableNameTypeServiceStub
                   builder.add("name", String.valueOf(request.getName()));
                   return builder.build();
                 })
+            .setResourceNameExtractor(request -> request.getName())
             .build();
     GrpcCallSettings<GetApiOperationRequest, ApiOperation> apiPagedTransportSettings =
         GrpcCallSettings.<GetApiOperationRequest, ApiOperation>newBuilder()
@@ -114,6 +115,7 @@ public class GrpcCallableNameTypeServiceStub extends CallableNameTypeServiceStub
                   builder.add("name", String.valueOf(request.getName()));
                   return builder.build();
                 })
+            .setResourceNameExtractor(request -> request.getName())
             .build();
 
     this.getApiOperationCallable =