fix: ensure render pipelines have at least 1 target

CHANGELOG.md

@@ -90,6 +90,10 @@ By @stefnotch in [#5410](https://github.com/gfx-rs/wgpu/pull/5410)
 
 ### Bug Fixes
 
+### General
+
+- Ensure render pipelines have at least 1 target. By @ErichDonGubler in [#5715](https://github.com/gfx-rs/wgpu/pull/5715)
+
 #### Vulkan
 
 - Fix enablement of subgroup ops extension on Vulkan devices that don't support Vulkan 1.3. By @cwfitzgerald in [#5624](https://github.com/gfx-rs/wgpu/pull/5624).

tests/tests/pipeline.rs

@@ -35,3 +35,46 @@ static PIPELINE_DEFAULT_LAYOUT_BAD_MODULE: GpuTestConfiguration = GpuTestConfigu
             pipeline.get_bind_group_layout(0);
         });
     });
+
+const TRIVIAL_VERTEX_SHADER_DESC: wgpu::ShaderModuleDescriptor = wgpu::ShaderModuleDescriptor {
+    label: Some("trivial vertex shader"),
+    source: wgpu::ShaderSource::Wgsl(std::borrow::Cow::Borrowed(
+        "@vertex fn main() -> @builtin(position) vec4<f32> { return vec4<f32>(0); }",
+    )),
+};
+
+#[gpu_test]
+static NO_TARGETLESS_RENDER: GpuTestConfiguration = GpuTestConfiguration::new()
+    .parameters(TestParameters::default())
+    .run_sync(|ctx| {
+        fail(&ctx.device, || {
+            // Testing multisampling is important, because some backends don't behave well if one
+            // tries to compile code in an unsupported multisample count. Failing to validate here
+            // has historically resulted in requesting the back end to compile code.
+            for power_of_two in [1, 2, 4, 8, 16, 32, 64] {
+                ctx.device
+                    .create_render_pipeline(&wgpu::RenderPipelineDescriptor {
+                        label: None,
+                        layout: None,
+                        vertex: wgpu::VertexState {
+                            module: &ctx.device.create_shader_module(TRIVIAL_VERTEX_SHADER_DESC),
+                            entry_point: "main",
+                            compilation_options: Default::default(),
+                            buffers: &[],
+                        },
+                        primitive: Default::default(),
+                        depth_stencil: None,
+                        multisample: wgpu::MultisampleState {
+                            count: power_of_two,
+                            ..Default::default()
+                        },
+                        fragment: None,
+                        multiview: None,
+                        cache: None,
+                    });
+            }
+        })
+        // TODO: concrete error message:
+        // At least one color attachment or depth-stencil attachment was expected, but no
+        // render target for the pipeline was specified.
+    });

wgpu-core/src/device/resource.rs

@@ -3044,8 +3044,11 @@ impl<A: HalApi> Device<A> {
             );
         }
 
+        let mut target_specified = false;
+
         for (i, cs) in color_targets.iter().enumerate() {
             if let Some(cs) = cs.as_ref() {
+                target_specified = true;
                 let error = loop {
                     if cs.write_mask.contains_invalid_bits() {
                         break Some(pipeline::ColorStateError::InvalidWriteMask(cs.write_mask));
@@ -3073,6 +3076,7 @@ impl<A: HalApi> Device<A> {
                     if !hal::FormatAspects::from(cs.format).contains(hal::FormatAspects::COLOR) {
                         break Some(pipeline::ColorStateError::FormatNotColor(cs.format));
                     }
+
                     if desc.multisample.count > 1
                         && !format_features
                             .flags
@@ -3091,6 +3095,7 @@ impl<A: HalApi> Device<A> {
                                 .supported_sample_counts(),
                         ));
                     }
+
                     if let Some(blend_mode) = cs.blend {
                         for factor in [
                             blend_mode.color.src_factor,
@@ -3130,6 +3135,7 @@ impl<A: HalApi> Device<A> {
         }
 
         if let Some(ds) = depth_stencil_state {
+            target_specified = true;
             let error = loop {
                 let format_features = self.describe_format_features(adapter, ds.format)?;
                 if !format_features
@@ -3180,6 +3186,10 @@ impl<A: HalApi> Device<A> {
             }
         }
 
+        if !target_specified {
+            return Err(pipeline::CreateRenderPipelineError::NoTargetSpecified);
+        }
+
         // Get the pipeline layout from the desc if it is provided.
         let pipeline_layout = match desc.layout {
             Some(pipeline_layout_id) => {

wgpu-core/src/pipeline.rs

@@ -495,6 +495,11 @@ pub enum CreateRenderPipelineError {
     PipelineExpectsShaderToUseDualSourceBlending,
     #[error("Shader entry point expects the pipeline to make use of dual-source blending.")]
     ShaderExpectsPipelineToUseDualSourceBlending,
+    #[error("{}", concat!(
+        "At least one color attachment or depth-stencil attachment was expected, ",
+        "but no render target for the pipeline was specified."
+    ))]
+    NoTargetSpecified,
 }
 
 bitflags::bitflags! {