feat: Add callable getters for non-eligible or non-enabled REST metho…

…ds (#1211)

This is a PR for Part 1 of #1117 (Override method with clearer exception messages for non-eligible and non-enabled Service RPCs). Opening this while I look at other possible approaches: 

Other approaches looked at/ to revisit:
- Override createCallableClassMembers to return Map<String, Expr> (Return either VariableExpr or ThrowExpr)
- Create a duplicate createCallableClassMembers (i.e. createInvalidCallableClassMembers) that copies functionality of createCallableClassMembers but returns Map<String, ThrowExpr>

Both approaches above had an issue when setting the return type for the callableGetter. ThrowExpr's type is always set as `UnsupportedOperationException` but the MethodDefinition's return type is not (i.e. for Streams it would be ServerStreamCallable or ClientStreamCallable/ Unary is UnaryCallable vs. Operation, etc.). Would need potentially need another mapping between callableName and method return type for ThrowExprs.

This PR's implementation is copied from: https://togithub.com/googleapis/gapic-generator-java/blob/8c5e17ba325b7711f9ba9501992ab48e736ffc18/gapic-generator-java/src/main/java/com/google/api/generator/gapic/composer/common/AbstractServiceStubClassComposer.java#L284-L302
- Use getCallableType(protoMethod) to get the correct return type for the RPC
- ThrowExpr's return type is set to `UnsupportedOperationException`

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

@@ -59,6 +59,7 @@
 import com.google.api.generator.gapic.model.Message;
 import com.google.api.generator.gapic.model.Method;
 import com.google.api.generator.gapic.model.Service;
+import com.google.api.generator.gapic.model.Transport;
 import com.google.api.generator.gapic.utils.JavaStyle;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
@@ -89,7 +90,7 @@ public abstract class AbstractTransportServiceStubClassComposer implements Class
   private static final String BACKGROUND_RESOURCES_MEMBER_NAME = "backgroundResources";
   private static final String CALLABLE_NAME = "Callable";
   private static final String CALLABLE_FACTORY_MEMBER_NAME = "callableFactory";
-  private static final String CALLABLE_CLASS_MEMBER_PATTERN = "%sCallable";
+  protected static final String CALLABLE_CLASS_MEMBER_PATTERN = "%sCallable";
   private static final String OPERATION_CALLABLE_CLASS_MEMBER_PATTERN = "%sOperationCallable";
   private static final String OPERATION_CALLABLE_NAME = "OperationCallable";
   // private static final String OPERATIONS_STUB_MEMBER_NAME = "operationsStub";
@@ -126,7 +127,8 @@ private static TypeStore createStaticTypes() {
             RequestParamsExtractor.class,
             ServerStreamingCallable.class,
             TimeUnit.class,
-            UnaryCallable.class);
+            UnaryCallable.class,
+            UnsupportedOperationException.class);
     return new TypeStore(concreteClazzes);
   }
 
@@ -190,6 +192,19 @@ public GapicClass generate(GapicContext context, Service service) {
             messageTypes,
             context.restNumericEnumsEnabled());
 
+    List<MethodDefinition> methodDefinitions =
+        createClassMethods(
+            context,
+            service,
+            typeStore,
+            classMemberVarExprs,
+            callableClassMemberVarExprs,
+            protoMethodNameToDescriptorVarExprs,
+            classStatements);
+    methodDefinitions.addAll(
+        createStubOverrideMethods(
+            classMemberVarExprs.get(BACKGROUND_RESOURCES_MEMBER_NAME), service));
+
     StubCommentComposer commentComposer =
         new StubCommentComposer(getTransportContext().transportNames().get(0));
 
@@ -204,22 +219,14 @@ public GapicClass generate(GapicContext context, Service service) {
             .setName(className)
             .setExtendsType(
                 typeStore.get(getTransportContext().classNames().getServiceStubClassName(service)))
-            .setMethods(
-                createClassMethods(
-                    context,
-                    service,
-                    typeStore,
-                    classMemberVarExprs,
-                    callableClassMemberVarExprs,
-                    protoMethodNameToDescriptorVarExprs,
-                    classStatements))
+            .setMethods(methodDefinitions)
             .setStatements(classStatements)
             .build();
     return GapicClass.create(kind, classDef);
   }
 
-  protected boolean isSupportedMethod(Method method) {
-    return true;
+  protected Transport getTransport() {
+    return Transport.GRPC;
   }
 
   protected abstract Statement createMethodDescriptorVariableDecl(
@@ -307,7 +314,7 @@ protected List<Statement> createMethodDescriptorVariableDecls(
       Map<String, Message> messageTypes,
       boolean restNumericEnumsEnabled) {
     return service.methods().stream()
-        .filter(this::isSupportedMethod)
+        .filter(x -> x.isSupportedByTransport(getTransport()))
         .map(
             m ->
                 createMethodDescriptorVariableDecl(
@@ -336,7 +343,7 @@ private static List<Statement> createClassMemberFieldDeclarations(
   protected Map<String, VariableExpr> createProtoMethodNameToDescriptorClassMembers(
       Service service, Class<?> descriptorClass) {
     return service.methods().stream()
-        .filter(this::isSupportedMethod)
+        .filter(x -> x.isSupportedByTransport(getTransport()))
         .collect(
             Collectors.toMap(
                 Method::name,
@@ -368,7 +375,7 @@ private Map<String, VariableExpr> createCallableClassMembers(
     Map<String, VariableExpr> callableClassMembers = new LinkedHashMap<>();
     // Using a for-loop because the output cardinality is not a 1:1 mapping to the input set.
     for (Method protoMethod : service.methods()) {
-      if (!isSupportedMethod(protoMethod)) {
+      if (!protoMethod.isSupportedByTransport(getTransport())) {
         continue;
       }
       String javaStyleProtoMethodName = JavaStyle.toLowerCamelCase(protoMethod.name());
@@ -470,9 +477,6 @@ protected List<MethodDefinition> createClassMethods(
             service,
             classMemberVarExprs.get(getTransportContext().transportOperationsStubNames().get(0))));
     javaMethods.addAll(createCallableGetterMethods(callableClassMemberVarExprs));
-    javaMethods.addAll(
-        createStubOverrideMethods(
-            classMemberVarExprs.get(BACKGROUND_RESOURCES_MEMBER_NAME), service));
     return javaMethods;
   }
 
@@ -660,7 +664,7 @@ protected List<MethodDefinition> createConstructorMethods(
     // Transport settings local variables.
     Map<String, VariableExpr> javaStyleMethodNameToTransportSettingsVarExprs =
         service.methods().stream()
-            .filter(this::isSupportedMethod)
+            .filter(x -> x.isSupportedByTransport(getTransport()))
             .collect(
                 Collectors.toMap(
                     m -> JavaStyle.toLowerCamelCase(m.name()),
@@ -684,7 +688,7 @@ protected List<MethodDefinition> createConstructorMethods(
 
     secondCtorExprs.addAll(
         service.methods().stream()
-            .filter(this::isSupportedMethod)
+            .filter(x -> x.isSupportedByTransport(getTransport()))
             .map(
                 m ->
                     createTransportSettingsInitExpr(
@@ -1055,7 +1059,7 @@ private List<MethodDefinition> createStubOverrideMethods(
 
   private boolean checkOperationPollingMethod(Service service) {
     return service.methods().stream()
-        .filter(this::isSupportedMethod)
+        .filter(x -> x.isSupportedByTransport(getTransport()))
         .anyMatch(Method::isOperationPollingMethod);
   }
 
@@ -1094,7 +1098,7 @@ private TypeStore createDynamicTypes(Service service, String stubPakkage) {
     typeStore.putAll(
         service.pakkage(),
         service.methods().stream()
-            .filter(this::isSupportedMethod)
+            .filter(x -> x.isSupportedByTransport(getTransport()))
             .filter(Method::isPaged)
             .map(m -> String.format(PAGED_RESPONSE_TYPE_NAME_PATTERN, m.name()))
             .collect(Collectors.toList()),
@@ -1103,7 +1107,7 @@ private TypeStore createDynamicTypes(Service service, String stubPakkage) {
     return typeStore;
   }
 
-  private static TypeNode getCallableType(Method protoMethod) {
+  protected static TypeNode getCallableType(Method protoMethod) {
     TypeNode callableType = FIXED_TYPESTORE.get("UnaryCallable");
     switch (protoMethod.stream()) {
       case CLIENT:

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

@@ -45,19 +45,21 @@
 import com.google.api.generator.engine.ast.Statement;
 import com.google.api.generator.engine.ast.StringObjectValue;
 import com.google.api.generator.engine.ast.ThisObjectValue;
+import com.google.api.generator.engine.ast.ThrowExpr;
 import com.google.api.generator.engine.ast.TypeNode;
 import com.google.api.generator.engine.ast.ValueExpr;
 import com.google.api.generator.engine.ast.VaporReference;
 import com.google.api.generator.engine.ast.Variable;
 import com.google.api.generator.engine.ast.VariableExpr;
 import com.google.api.generator.gapic.composer.common.AbstractTransportServiceStubClassComposer;
 import com.google.api.generator.gapic.composer.store.TypeStore;
+import com.google.api.generator.gapic.model.GapicContext;
 import com.google.api.generator.gapic.model.HttpBindings.HttpBinding;
 import com.google.api.generator.gapic.model.Message;
 import com.google.api.generator.gapic.model.Method;
-import com.google.api.generator.gapic.model.Method.Stream;
 import com.google.api.generator.gapic.model.OperationResponse;
 import com.google.api.generator.gapic.model.Service;
+import com.google.api.generator.gapic.model.Transport;
 import com.google.api.generator.gapic.utils.JavaStyle;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.BiMap;
@@ -115,10 +117,9 @@ private static TypeStore createStaticTypes() {
             TypeRegistry.class));
   }
 
-  protected boolean isSupportedMethod(Method method) {
-    return method.httpBindings() != null
-        && method.stream() != Stream.BIDI
-        && method.stream() != Stream.CLIENT;
+  @Override
+  protected Transport getTransport() {
+    return Transport.REST;
   }
 
   @Override
@@ -1248,4 +1249,56 @@ protected List<Statement> createTypeRegistry(Service service) {
                 .setValueExpr(typeRegistryBuilderExpr)
                 .build()));
   }
+
+  @Override
+  protected List<MethodDefinition> createClassMethods(
+      GapicContext context,
+      Service service,
+      TypeStore typeStore,
+      Map<String, VariableExpr> classMemberVarExprs,
+      Map<String, VariableExpr> callableClassMemberVarExprs,
+      Map<String, VariableExpr> protoMethodNameToDescriptorVarExprs,
+      List<Statement> classStatements) {
+    List<MethodDefinition> javaMethods = new ArrayList<>();
+    javaMethods.addAll(
+        super.createClassMethods(
+            context,
+            service,
+            typeStore,
+            classMemberVarExprs,
+            callableClassMemberVarExprs,
+            protoMethodNameToDescriptorVarExprs,
+            classStatements));
+    javaMethods.addAll(createInvalidClassMethods(service));
+    return javaMethods;
+  }
+
+  private List<MethodDefinition> createInvalidClassMethods(Service service) {
+    List<MethodDefinition> methodDefinitions = new ArrayList<>();
+    for (Method protoMethod : service.methods()) {
+      if (protoMethod.isSupportedByTransport(getTransport())) {
+        continue;
+      }
+      String javaStyleProtoMethodName = JavaStyle.toLowerCamelCase(protoMethod.name());
+      String callableName = String.format(CALLABLE_CLASS_MEMBER_PATTERN, javaStyleProtoMethodName);
+      methodDefinitions.add(
+          MethodDefinition.builder()
+              .setIsOverride(true)
+              .setScope(ScopeNode.PUBLIC)
+              .setName(callableName)
+              .setReturnType(getCallableType(protoMethod))
+              .setBody(
+                  Arrays.asList(
+                      ExprStatement.withExpr(
+                          ThrowExpr.builder()
+                              .setType(FIXED_TYPESTORE.get("UnsupportedOperationException"))
+                              .setMessageExpr(
+                                  String.format(
+                                      "Not implemented: %s(). %s transport is not implemented for this method yet.",
+                                      callableName, getTransport()))
+                              .build())))
+              .build());
+    }
+    return methodDefinitions;
+  }
 }

gapic-generator-java/src/main/java/com/google/api/generator/gapic/model/Method.java

@@ -99,6 +99,25 @@ public boolean isOperationPollingMethod() {
     return operationPollingMethod();
   }
 
+  /**
+   * Determines if method is both eligible and enabled for the Transport. GRPC+REST Transport is not
+   * supported as each transport's sub composers will invoke this method the specific transport
+   * (GRPC or REST)
+   *
+   * @param transport Expects either GRPC or REST Transport
+   * @return boolean if method should be generated for the transport
+   */
+  public boolean isSupportedByTransport(Transport transport) {
+    if (transport == Transport.REST) {
+      return httpBindings() != null && stream() != Stream.BIDI && stream() != Stream.CLIENT;
+    } else if (transport == Transport.GRPC) {
+      return true;
+    } else {
+      throw new IllegalArgumentException(
+          String.format("Invalid Transport: %s. Expecting GRPC or REST", transport.name()));
+    }
+  }
+
   public abstract Builder toBuilder();
 
   public static Builder builder() {

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

@@ -16,6 +16,7 @@ import com.google.api.gax.httpjson.ProtoMessageResponseParser;
 import com.google.api.gax.httpjson.ProtoRestSerializer;
 import com.google.api.gax.httpjson.longrunning.stub.HttpJsonOperationsStub;
 import com.google.api.gax.longrunning.OperationSnapshot;
+import com.google.api.gax.rpc.BidiStreamingCallable;
 import com.google.api.gax.rpc.ClientContext;
 import com.google.api.gax.rpc.OperationCallable;
 import com.google.api.gax.rpc.ServerStreamingCallable;
@@ -544,6 +545,18 @@ public class HttpJsonEchoStub extends EchoStub {
     return nestedBindingCallable;
   }
 
+  @Override
+  public BidiStreamingCallable<EchoRequest, EchoResponse> chatCallable() {
+    throw new UnsupportedOperationException(
+        "Not implemented: chatCallable(). REST transport is not implemented for this method yet.");
+  }
+
+  @Override
+  public UnaryCallable<EchoRequest, EchoResponse> noBindingCallable() {
+    throw new UnsupportedOperationException(
+        "Not implemented: noBindingCallable(). REST transport is not implemented for this method yet.");
+  }
+
   @Override
   public final void close() {
     try {

gapic-generator-java/src/test/java/com/google/api/generator/gapic/model/MethodTest.java

@@ -15,6 +15,7 @@
 package com.google.api.generator.gapic.model;
 
 import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertThrows;
 
 import com.google.api.generator.engine.ast.TypeNode;
 import com.google.api.generator.gapic.model.HttpBindings.HttpBinding;
@@ -112,4 +113,61 @@ public void shouldSetParamsExtractor_shouldReturnFalseIfHasNoHttpBindingsAndNoRo
     Method method = METHOD.toBuilder().setHttpBindings(null).setRoutingHeaderRule(null).build();
     assertThat(method.shouldSetParamsExtractor()).isFalse();
   }
+
+  @Test
+  public void
+      isSupportedByTransport_shouldReturnTrueIfHasHttpBindingsAndIsRESTEligibleForRESTTransport() {
+    Method methodNoStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.NONE).build();
+    assertThat(methodNoStreaming.isSupportedByTransport(Transport.REST)).isTrue();
+    Method methodServerSideStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.SERVER).build();
+    assertThat(methodServerSideStreaming.isSupportedByTransport(Transport.REST)).isTrue();
+  }
+
+  @Test
+  public void isSupportedByTransport_shouldReturnFalseIfNoHttpBindingsForRESTTransport() {
+    Method methodNoStreaming =
+        METHOD.toBuilder().setHttpBindings(null).setStream(Method.Stream.NONE).build();
+    assertThat(methodNoStreaming.isSupportedByTransport(Transport.REST)).isFalse();
+    Method methodServerSideStreaming =
+        METHOD.toBuilder().setHttpBindings(null).setStream(Method.Stream.SERVER).build();
+    assertThat(methodServerSideStreaming.isSupportedByTransport(Transport.REST)).isFalse();
+  }
+
+  @Test
+  public void
+      isSupportedByTransport_shouldReturnFalseIfHasHttpBindingsAndIsNotRESTEligibleForRESTTransport() {
+    Method methodClientSideStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.CLIENT).build();
+    assertThat(methodClientSideStreaming.isSupportedByTransport(Transport.REST)).isFalse();
+    Method methodBiDiStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.BIDI).build();
+    assertThat(methodBiDiStreaming.isSupportedByTransport(Transport.REST)).isFalse();
+  }
+
+  @Test
+  public void isSupportedByTransport_shouldReturnTrueForGRPCTransport() {
+    Method methodNoStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.NONE).build();
+    assertThat(methodNoStreaming.isSupportedByTransport(Transport.GRPC)).isTrue();
+    Method methodBiDiStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.BIDI).build();
+    assertThat(methodBiDiStreaming.isSupportedByTransport(Transport.GRPC)).isTrue();
+    Method methodNoStreamingNoHttpBindings =
+        METHOD.toBuilder().setStream(Method.Stream.NONE).build();
+    assertThat(methodNoStreamingNoHttpBindings.isSupportedByTransport(Transport.GRPC)).isTrue();
+    Method methodBiDiStreamingNoHttpBindings =
+        METHOD.toBuilder().setStream(Method.Stream.BIDI).build();
+    assertThat(methodBiDiStreamingNoHttpBindings.isSupportedByTransport(Transport.GRPC)).isTrue();
+  }
+
+  @Test
+  public void isSupportedByTransport_shouldThrowExceptionIfPassedGRPCRESTTransport() {
+    Method methodClientStreaming =
+        METHOD.toBuilder().setHttpBindings(HTTP_BINDINGS).setStream(Method.Stream.CLIENT).build();
+    assertThrows(
+        IllegalArgumentException.class,
+        () -> methodClientStreaming.isSupportedByTransport(Transport.GRPC_REST));
+  }
 }