Wire: Add support for nullptr objects as arguments

BUG=dawn:5

Change-Id: I84c80796e9bdfbcf59fafdd38d33ab2101a1d795
Reviewed-on: https://dawn-review.googlesource.com/1541
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

generator/templates/dawn_wire/WireClient.cpp

@@ -215,6 +215,9 @@ namespace dawn_wire {
                 // Implementation of the ObjectIdProvider interface
                 {% for type in by_category["object"] %}
                     ObjectId GetId({{as_cType(type.name)}} object) const override {
+                        if (object == nullptr) {
+                            return 0;
+                        }
                         return reinterpret_cast<{{as_wireType(type)}}>(object)->id;
                     }
                 {% endfor %}

generator/templates/dawn_wire/WireServer.cpp

@@ -358,6 +358,11 @@ namespace dawn_wire {
                 // Implementation of the ObjectIdResolver interface
                 {% for type in by_category["object"] %}
                     DeserializeResult GetFromId(ObjectId id, {{as_cType(type.name)}}* out) const override {
+                        if (id == 0) {
+                            *out = nullptr;
+                            return DeserializeResult::Success;
+                        }
+
                         auto data = mKnown{{type.name.CamelCase()}}.Get(id);
                         if (data == nullptr) {
                             return DeserializeResult::FatalError;

src/tests/unittests/WireTests.cpp

@@ -328,7 +328,7 @@ TEST_F(WireTests, CStringArgument) {
 }
 
 // Test that the wire is able to send objects as value arguments
-TEST_F(WireTests, DISABLED_ObjectAsValueArgument) {
+TEST_F(WireTests, ObjectAsValueArgument) {
     // Create pipeline
     dawnComputePipelineDescriptor pipelineDesc;
     pipelineDesc.nextInChain = nullptr;
@@ -485,6 +485,46 @@ TEST_F(WireTests, StructureOfStructureArrayArgument) {
     FlushClient();
 }
 
+// Test passing nullptr instead of objects - object as value version
+TEST_F(WireTests, NullptrAsValue) {
+    dawnCommandBufferBuilder builder = dawnDeviceCreateCommandBufferBuilder(device);
+    dawnComputePassEncoder pass = dawnCommandBufferBuilderBeginComputePass(builder);
+    dawnComputePassEncoderSetComputePipeline(pass, nullptr);
+
+    dawnCommandBufferBuilder apiBuilder = api.GetNewCommandBufferBuilder();
+    EXPECT_CALL(api, DeviceCreateCommandBufferBuilder(apiDevice))
+        .WillOnce(Return(apiBuilder));
+
+    dawnComputePassEncoder apiPass = api.GetNewComputePassEncoder();
+    EXPECT_CALL(api, CommandBufferBuilderBeginComputePass(apiBuilder))
+        .WillOnce(Return(apiPass));
+
+    EXPECT_CALL(api, ComputePassEncoderSetComputePipeline(apiPass, nullptr))
+        .Times(1);
+
+    FlushClient();
+}
+
+// Test passing nullptr instead of objects - array of objects version
+TEST_F(WireTests, NullptrInArray) {
+    dawnBindGroupLayout nullBGL = nullptr;
+
+    dawnPipelineLayoutDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.numBindGroupLayouts = 1;
+    descriptor.bindGroupLayouts = &nullBGL;
+
+    dawnDeviceCreatePipelineLayout(device, &descriptor);
+    EXPECT_CALL(api, DeviceCreatePipelineLayout(apiDevice, MatchesLambda([](const dawnPipelineLayoutDescriptor* desc) -> bool {
+        return desc->nextInChain == nullptr &&
+            desc->numBindGroupLayouts == 1 &&
+            desc->bindGroupLayouts[0] == nullptr;
+    })))
+        .WillOnce(Return(nullptr));
+
+    FlushClient();
+}
+
 // Test that the server doesn't forward calls to error objects or with error objects
 // Also test that when GetResult is called on an error builder, the error callback is fired
 // TODO(cwallez@chromium.org): This test is disabled because the introduction of encoders breaks