Add test for fragment outputs not covered by render attachments

Bug: dawn:962
Change-Id: I26412b8db598dc581f1c302f39e65dc0c45aa443
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/56802
Auto-Submit: Austin Eng <enga@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/tests/BUILD.gn

@@ -336,6 +336,7 @@ source_set("dawn_end2end_tests_sources") {
     "end2end/QueryTests.cpp",
     "end2end/QueueTests.cpp",
     "end2end/QueueTimelineTests.cpp",
+    "end2end/RenderAttachmentTests.cpp",
     "end2end/RenderBundleTests.cpp",
     "end2end/RenderPassLoadOpTests.cpp",
     "end2end/RenderPassTests.cpp",

src/tests/end2end/RenderAttachmentTests.cpp

@@ -0,0 +1,84 @@
+// Copyright 2021 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "tests/DawnTest.h"
+
+#include "utils/ComboRenderPipelineDescriptor.h"
+#include "utils/WGPUHelpers.h"
+
+class RenderAttachmentTest : public DawnTest {};
+
+// Test that it is ok to have more fragment outputs than color attachments.
+// There should be no backend validation errors or indexing out-of-bounds.
+TEST_P(RenderAttachmentTest, MoreFragmentOutputsThanAttachments) {
+    wgpu::ShaderModule vsModule = utils::CreateShaderModule(device, R"(
+        [[stage(vertex)]]
+        fn main() -> [[builtin(position)]] vec4<f32> {
+            return vec4<f32>(0.0, 0.0, 0.0, 1.0);
+        })");
+
+    wgpu::ShaderModule fsModule = utils::CreateShaderModule(device, R"(
+        struct Output {
+            [[location(0)]] color0 : vec4<f32>;
+            [[location(1)]] color1 : vec4<f32>;
+            [[location(2)]] color2 : vec4<f32>;
+            [[location(3)]] color3 : vec4<f32>;
+        };
+
+        [[stage(fragment)]]
+        fn main() -> Output {
+            var output : Output;
+            output.color0 = vec4<f32>(1.0, 0.0, 0.0, 1.0);
+            output.color1 = vec4<f32>(0.0, 1.0, 0.0, 1.0);
+            output.color2 = vec4<f32>(0.0, 0.0, 1.0, 1.0);
+            output.color3 = vec4<f32>(1.0, 1.0, 0.0, 1.0);
+            return output;
+        })");
+
+    // Fragment outputs 1, 2, 3 are written in the shader, but unused by the pipeline.
+    utils::ComboRenderPipelineDescriptor pipelineDesc;
+    pipelineDesc.vertex.module = vsModule;
+    pipelineDesc.cFragment.module = fsModule;
+    pipelineDesc.primitive.topology = wgpu::PrimitiveTopology::PointList;
+    pipelineDesc.cTargets[0].format = wgpu::TextureFormat::RGBA8Unorm;
+    pipelineDesc.cFragment.targetCount = 1;
+
+    wgpu::RenderPipeline pipeline = device.CreateRenderPipeline(&pipelineDesc);
+
+    wgpu::CommandEncoder encoder = device.CreateCommandEncoder();
+
+    wgpu::TextureDescriptor textureDesc;
+    textureDesc.size = {1, 1, 1};
+    textureDesc.format = wgpu::TextureFormat::RGBA8Unorm;
+    textureDesc.usage = wgpu::TextureUsage::RenderAttachment | wgpu::TextureUsage::CopySrc;
+
+    wgpu::Texture renderTarget = device.CreateTexture(&textureDesc);
+    utils::ComboRenderPassDescriptor renderPass({renderTarget.CreateView()});
+    wgpu::RenderPassEncoder pass = encoder.BeginRenderPass(&renderPass);
+    pass.SetPipeline(pipeline);
+    pass.Draw(1);
+    pass.EndPass();
+    wgpu::CommandBuffer commands = encoder.Finish();
+    queue.Submit(1, &commands);
+
+    EXPECT_PIXEL_RGBA8_EQ(RGBA8::kRed, renderTarget, 0, 0);
+}
+
+DAWN_INSTANTIATE_TEST(RenderAttachmentTest,
+                      D3D12Backend(),
+                      D3D12Backend({}, {"use_d3d12_render_pass"}),
+                      MetalBackend(),
+                      OpenGLBackend(),
+                      OpenGLESBackend(),
+                      VulkanBackend());