feat: Lambda-ize single-method anon classes (#815)

src/main/java/com/google/api/generator/engine/ast/MethodInvocationExpr.java

@@ -126,6 +126,9 @@ public MethodInvocationExpr build() {
           "generics",
           String.format("method invocation of %s", methodInvocationExpr.methodIdentifier().name()));
 
+      // TODO(v2): If type-checking is ever added for arguments, beware of lambdas and their type
+      // workarounds.
+
       return methodInvocationExpr;
     }
   }

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

@@ -613,13 +613,13 @@ private static Expr createPagedListDescriptorAssignExpr(
               .setReturnType(returnType)
               .build();
       thenExpr =
-              MethodInvocationExpr.builder()
-                  .setStaticReferenceType(
-                      TypeNode.withReference(ConcreteReference.withClazz(ImmutableList.class)))
-                  .setGenerics(Arrays.asList(repeatedResponseType.reference()))
-                  .setMethodName("of")
-                  .setReturnType(returnType)
-                  .build();
+          MethodInvocationExpr.builder()
+              .setStaticReferenceType(
+                  TypeNode.withReference(ConcreteReference.withClazz(ImmutableList.class)))
+              .setGenerics(Arrays.asList(repeatedResponseType.reference()))
+              .setMethodName("of")
+              .setReturnType(returnType)
+              .build();
       elseExpr = getResponsesExpr;
     }
     // While protobufs should not be null, this null-check is needed to protect against NPEs

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

@@ -30,14 +30,14 @@
 import com.google.api.gax.rpc.ServerStreamingCallable;
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.api.generator.engine.ast.AnnotationNode;
-import com.google.api.generator.engine.ast.AnonymousClassExpr;
 import com.google.api.generator.engine.ast.AssignmentExpr;
 import com.google.api.generator.engine.ast.CastExpr;
 import com.google.api.generator.engine.ast.ClassDefinition;
 import com.google.api.generator.engine.ast.CommentStatement;
 import com.google.api.generator.engine.ast.ConcreteReference;
 import com.google.api.generator.engine.ast.Expr;
 import com.google.api.generator.engine.ast.ExprStatement;
+import com.google.api.generator.engine.ast.LambdaExpr;
 import com.google.api.generator.engine.ast.MethodDefinition;
 import com.google.api.generator.engine.ast.MethodInvocationExpr;
 import com.google.api.generator.engine.ast.NewObjectExpr;
@@ -1165,23 +1165,14 @@ private static ClassDefinition createNestedRpcPagedResponseClass(
                 .setClazz(ApiFunction.class)
                 .setGenerics(Arrays.asList(methodPageType.reference(), thisClassType.reference()))
                 .build());
+
+    // Overrides ApiFunction.apply.
+    // (https://github.com/googleapis/api-common-java/blob/debf25960dea0367b0d3b5e16d57d76c1d01947e/src/main/java/com/google/api/core/ApiFunction.java).
     Expr pageToTransformExpr =
-        AnonymousClassExpr.builder()
-            .setType(anonClassType)
-            .setMethods(
-                Arrays.asList(
-                    MethodDefinition.builder()
-                        .setIsOverride(true)
-                        .setScope(ScopeNode.PUBLIC)
-                        .setReturnType(thisClassType)
-                        .setName("apply")
-                        .setArguments(inputVarExpr.toBuilder().setIsDecl(true).build())
-                        .setReturnExpr(
-                            NewObjectExpr.builder()
-                                .setType(thisClassType)
-                                .setArguments(inputVarExpr)
-                                .build())
-                        .build()))
+        LambdaExpr.builder()
+            .setArguments(inputVarExpr.toBuilder().setIsDecl(true).build())
+            .setReturnExpr(
+                NewObjectExpr.builder().setType(thisClassType).setArguments(inputVarExpr).build())
             .build();
 
     // createAsync method - return expression.
@@ -1739,9 +1730,7 @@ private static boolean isProtoEmptyType(TypeNode type) {
   private static void updateGapicMetadata(
       GapicContext context, String protoPackage, String javaPackage) {
     context.updateGapicMetadata(
-        context
-            .gapicMetadata()
-            .toBuilder()
+        context.gapicMetadata().toBuilder()
             .setProtoPackage(protoPackage)
             .setLibraryPackage(javaPackage)
             .build());

src/main/java/com/google/api/generator/gapic/composer/grpc/GrpcServiceStubClassComposer.java

@@ -16,13 +16,12 @@
 
 import com.google.api.gax.grpc.GrpcCallSettings;
 import com.google.api.gax.grpc.GrpcStubCallableFactory;
-import com.google.api.gax.rpc.RequestParamsExtractor;
-import com.google.api.generator.engine.ast.AnonymousClassExpr;
 import com.google.api.generator.engine.ast.AssignmentExpr;
 import com.google.api.generator.engine.ast.ConcreteReference;
 import com.google.api.generator.engine.ast.EnumRefExpr;
 import com.google.api.generator.engine.ast.Expr;
 import com.google.api.generator.engine.ast.ExprStatement;
+import com.google.api.generator.engine.ast.LambdaExpr;
 import com.google.api.generator.engine.ast.MethodDefinition;
 import com.google.api.generator.engine.ast.MethodInvocationExpr;
 import com.google.api.generator.engine.ast.ScopeNode;
@@ -223,7 +222,7 @@ protected Expr createTransportSettingsInitExpr(
           MethodInvocationExpr.builder()
               .setExprReferenceExpr(callSettingsBuilderExpr)
               .setMethodName("setParamsExtractor")
-              .setArguments(createRequestParamsExtractorAnonClass(method))
+              .setArguments(createRequestParamsExtractorClassInstance(method))
               .build();
     }
 
@@ -255,7 +254,7 @@ protected String getProtoRpcFullMethodName(Service protoService, Method protoMet
     return String.format("google.iam.v1.IAMPolicy/%s", protoMethod.name());
   }
 
-  private AnonymousClassExpr createRequestParamsExtractorAnonClass(Method method) {
+  private LambdaExpr createRequestParamsExtractorClassInstance(Method method) {
     Preconditions.checkState(
         method.hasHttpBindings(), String.format("Method %s has no HTTP binding", method.name()));
 
@@ -339,24 +338,13 @@ private AnonymousClassExpr createRequestParamsExtractorAnonClass(Method method)
             .setReturnType(returnType)
             .build();
 
-    MethodDefinition extractMethod =
-        MethodDefinition.builder()
-            .setIsOverride(true)
-            .setScope(ScopeNode.PUBLIC)
-            .setReturnType(returnType)
-            .setName("extract")
-            .setArguments(requestVarExpr.toBuilder().setIsDecl(true).build())
-            .setBody(
-                bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList()))
-            .setReturnExpr(returnExpr)
-            .build();
-
-    TypeNode anonClassType =
-        TypeNode.withReference(
-            ConcreteReference.builder()
-                .setClazz(RequestParamsExtractor.class)
-                .setGenerics(method.inputType().reference())
-                .build());
-    return AnonymousClassExpr.builder().setType(anonClassType).setMethods(extractMethod).build();
+    // Overrides extract().
+    // https://github.com/googleapis/gax-java/blob/8d45d186e36ae97b789a6f89d80ae5213a773b65/gax/src/main/java/com/google/api/gax/rpc/RequestParamsExtractor.java#L55
+    return LambdaExpr.builder()
+        .setArguments(requestVarExpr.toBuilder().setIsDecl(true).build())
+        .setBody(
+            bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList()))
+        .setReturnExpr(returnExpr)
+        .build();
   }
 }

src/main/java/com/google/api/generator/gapic/composer/grpc/MockServiceImplClassComposer.java

@@ -354,7 +354,7 @@ private static MethodDefinition createGenericClientStreamingProtoMethodOverride(
                     AssignmentExpr.builder()
                         .setVariableExpr(requestObserverVarExpr.toBuilder().setIsDecl(true).build())
                         .setValueExpr(
-                            createStreamObserverAnonymousClassExpr(
+                            createStreamObserverClassInstance(
                                 protoMethod,
                                 returnType,
                                 responseObserverVarExpr,
@@ -364,7 +364,7 @@ private static MethodDefinition createGenericClientStreamingProtoMethodOverride(
         .build();
   }
 
-  private static AnonymousClassExpr createStreamObserverAnonymousClassExpr(
+  private static AnonymousClassExpr createStreamObserverClassInstance(
       Method protoMethod,
       TypeNode classType,
       VariableExpr responseObserverVarExpr,

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

@@ -24,13 +24,13 @@
 import com.google.api.gax.httpjson.ProtoMessageResponseParser;
 import com.google.api.gax.httpjson.ProtoRestSerializer;
 import com.google.api.generator.engine.ast.AnnotationNode;
-import com.google.api.generator.engine.ast.AnonymousClassExpr;
 import com.google.api.generator.engine.ast.AssignmentExpr;
 import com.google.api.generator.engine.ast.ConcreteReference;
 import com.google.api.generator.engine.ast.EnumRefExpr;
 import com.google.api.generator.engine.ast.Expr;
 import com.google.api.generator.engine.ast.ExprStatement;
 import com.google.api.generator.engine.ast.IfStatement;
+import com.google.api.generator.engine.ast.LambdaExpr;
 import com.google.api.generator.engine.ast.MethodDefinition;
 import com.google.api.generator.engine.ast.MethodInvocationExpr;
 import com.google.api.generator.engine.ast.NewObjectExpr;
@@ -277,7 +277,7 @@ private List<Expr> getRequestFormatterExpr(Method protoMethod) {
                     ValueExpr.withValue(
                         StringObjectValue.withValue(
                             protoMethod.httpBindings().patternLowerCamel())),
-                    createFieldsExtractorAnonClass(
+                    createFieldsExtractorClassInstance(
                         protoMethod,
                         extractorVarType,
                         protoMethod.httpBindings().pathParameters(),
@@ -303,7 +303,7 @@ private List<Expr> getRequestFormatterExpr(Method protoMethod) {
             .apply(
                 "setQueryParamsExtractor",
                 Arrays.asList(
-                    createFieldsExtractorAnonClass(
+                    createFieldsExtractorClassInstance(
                         protoMethod,
                         extractorVarType,
                         protoMethod.httpBindings().queryParameters(),
@@ -316,7 +316,7 @@ private List<Expr> getRequestFormatterExpr(Method protoMethod) {
             .apply(
                 "setRequestBodyExtractor",
                 Arrays.asList(
-                    createFieldsExtractorAnonClass(
+                    createFieldsExtractorClassInstance(
                         protoMethod,
                         extractorVarType,
                         protoMethod.httpBindings().bodyParameters(),
@@ -356,7 +356,7 @@ private List<Expr> setResponseParserExpr(Method protoMethod) {
     return Collections.singletonList(expr);
   }
 
-  private Expr createFieldsExtractorAnonClass(
+  private Expr createFieldsExtractorClassInstance(
       Method method,
       TypeNode extractorReturnType,
       Set<HttpBinding> httpBindingFieldNames,
@@ -495,25 +495,13 @@ private Expr createFieldsExtractorAnonClass(
       }
     }
 
-    MethodDefinition extractMethod =
-        MethodDefinition.builder()
-            .setIsOverride(true)
-            .setScope(ScopeNode.PUBLIC)
-            .setReturnType(extractorReturnType)
-            .setName("extract")
-            .setArguments(requestVarExpr.toBuilder().setIsDecl(true).build())
-            .setBody(bodyStatements)
-            .setReturnExpr(returnExpr)
-            .build();
-
-    TypeNode anonClassType =
-        TypeNode.withReference(
-            ConcreteReference.builder()
-                .setClazz(FieldsExtractor.class)
-                .setGenerics(method.inputType().reference(), extractorReturnType.reference())
-                .build());
-
-    return AnonymousClassExpr.builder().setType(anonClassType).setMethods(extractMethod).build();
+    // Overrides FieldsExtractor
+    // (https://github.com/googleapis/gax-java/blob/12b18ee255d3fabe13bb3969df40753b29f830d5/gax-httpjson/src/main/java/com/google/api/gax/httpjson/FieldsExtractor.java).
+    return LambdaExpr.builder()
+        .setArguments(requestVarExpr.toBuilder().setIsDecl(true).build())
+        .setBody(bodyStatements)
+        .setReturnExpr(returnExpr)
+        .build();
   }
 
   private List<Expr> getHttpMethodTypeExpr(Method protoMethod) {

src/test/java/com/google/api/generator/gapic/composer/common/goldens/EchoClient.golden

@@ -1,6 +1,5 @@
 package com.google.showcase.v1beta1;
 
-import com.google.api.core.ApiFunction;
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutures;
 import com.google.api.core.BetaApi;
@@ -860,14 +859,7 @@ public class EchoClient implements BackgroundResource {
       ApiFuture<PagedExpandPage> futurePage =
           PagedExpandPage.createEmptyPage().createPageAsync(context, futureResponse);
       return ApiFutures.transform(
-          futurePage,
-          new ApiFunction<PagedExpandPage, PagedExpandPagedResponse>() {
-            @Override
-            public PagedExpandPagedResponse apply(PagedExpandPage input) {
-              return new PagedExpandPagedResponse(input);
-            }
-          },
-          MoreExecutors.directExecutor());
+          futurePage, input -> new PagedExpandPagedResponse(input), MoreExecutors.directExecutor());
     }
 
     private PagedExpandPagedResponse(PagedExpandPage page) {
@@ -941,12 +933,7 @@ public class EchoClient implements BackgroundResource {
           SimplePagedExpandPage.createEmptyPage().createPageAsync(context, futureResponse);
       return ApiFutures.transform(
           futurePage,
-          new ApiFunction<SimplePagedExpandPage, SimplePagedExpandPagedResponse>() {
-            @Override
-            public SimplePagedExpandPagedResponse apply(SimplePagedExpandPage input) {
-              return new SimplePagedExpandPagedResponse(input);
-            }
-          },
+          input -> new SimplePagedExpandPagedResponse(input),
           MoreExecutors.directExecutor());
     }
 

src/test/java/com/google/api/generator/gapic/composer/common/goldens/IdentityClient.golden

@@ -1,6 +1,5 @@
 package com.google.showcase.v1beta1;
 
-import com.google.api.core.ApiFunction;
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutures;
 import com.google.api.core.BetaApi;
@@ -644,14 +643,7 @@ public class IdentityClient implements BackgroundResource {
       ApiFuture<ListUsersPage> futurePage =
           ListUsersPage.createEmptyPage().createPageAsync(context, futureResponse);
       return ApiFutures.transform(
-          futurePage,
-          new ApiFunction<ListUsersPage, ListUsersPagedResponse>() {
-            @Override
-            public ListUsersPagedResponse apply(ListUsersPage input) {
-              return new ListUsersPagedResponse(input);
-            }
-          },
-          MoreExecutors.directExecutor());
+          futurePage, input -> new ListUsersPagedResponse(input), MoreExecutors.directExecutor());
     }
 
     private ListUsersPagedResponse(ListUsersPage page) {