Implement CreateBufferMapped in dawn_native for MAP_WRITE buffers only.

This is the first command to return a struct. This patch also
updates the code generator to support structure return values.

Bug: dawn:7
Change-Id: Ie8acec895c0ec88429672138ffc900032fbbc447
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/4780
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/tests/end2end/BufferTests.cpp

@@ -229,3 +229,48 @@ DAWN_INSTANTIATE_TEST(BufferSetSubDataTests,
                      MetalBackend,
                      OpenGLBackend,
                      VulkanBackend);
+
+class CreateBufferMappedTests : public DawnTest {};
+
+// Test that the simplest CreateBufferMapped works.
+TEST_P(CreateBufferMappedTests, SmallSyncWrite) {
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = 4;
+    descriptor.usage = dawn::BufferUsageBit::MapWrite | dawn::BufferUsageBit::TransferSrc;
+
+    uint32_t myData = 230502;
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    memcpy(result.data, &myData, sizeof(myData));
+    result.buffer.Unmap();
+
+    EXPECT_BUFFER_U32_EQ(myData, result.buffer, 0);
+}
+
+// Test CreateBufferMapped for a large buffer
+TEST_P(CreateBufferMappedTests, LargeSyncWrite) {
+    constexpr uint64_t kDataSize = 1000 * 1000;
+    std::vector<uint32_t> myData;
+    for (uint32_t i = 0; i < kDataSize; ++i) {
+        myData.push_back(i);
+    }
+
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = static_cast<uint64_t>(kDataSize * sizeof(uint32_t));
+    descriptor.usage = dawn::BufferUsageBit::MapWrite | dawn::BufferUsageBit::TransferSrc;
+
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    memcpy(result.data, myData.data(), kDataSize * sizeof(uint32_t));
+    result.buffer.Unmap();
+
+    EXPECT_BUFFER_U32_RANGE_EQ(myData.data(), result.buffer, 0, kDataSize);
+}
+
+DAWN_INSTANTIATE_TEST(CreateBufferMappedTests,
+                      D3D12Backend,
+                      MetalBackend,
+                      OpenGLBackend,
+                      VulkanBackend);

src/tests/unittests/validation/BufferValidationTests.cpp

@@ -82,6 +82,15 @@ class BufferValidationTest : public ValidationTest {
             return device.CreateBuffer(&descriptor);
         }
 
+        dawn::CreateBufferMappedResult CreateBufferMapped(uint64_t size,
+                                                          dawn::BufferUsageBit usage) {
+            dawn::BufferDescriptor descriptor;
+            descriptor.size = size;
+            descriptor.usage = usage;
+
+            return device.CreateBufferMapped(&descriptor);
+        }
+
         dawn::Queue queue;
 
     private:
@@ -183,6 +192,14 @@ TEST_F(BufferValidationTest, MapWriteSuccess) {
     buf.Unmap();
 }
 
+// Test the success case for CreateBufferMapped
+TEST_F(BufferValidationTest, CreateBufferMappedSuccess) {
+    dawn::CreateBufferMappedResult result = CreateBufferMapped(4, dawn::BufferUsageBit::MapWrite);
+    ASSERT_NE(result.data, nullptr);
+    ASSERT_EQ(result.dataLength, 4u);
+    result.buffer.Unmap();
+}
+
 // Test map reading a buffer with wrong current usage
 TEST_F(BufferValidationTest, MapReadWrongUsage) {
     dawn::BufferDescriptor descriptor;