Allow fragment stage to have more outputs than the pipeline has (#2822)

Author: jinleili

wgpu-core/src/device/mod.rs

@@ -2774,16 +2774,14 @@ impl<A: HalApi> Device<A> {
                             },
                         )?;
                     }
-                    Some(&None) => {
-                        return Err(
-                            pipeline::CreateRenderPipelineError::InvalidFragmentOutputLocation(*i),
-                        );
-                    }
                     _ => {
-                        return Err(pipeline::CreateRenderPipelineError::ColorState(
-                            *i as u8,
-                            pipeline::ColorStateError::Missing,
-                        ));
+                        log::info!(
+                            "The fragment stage {:?} output @location({}) values are ignored",
+                            fragment_stage
+                                .as_ref()
+                                .map_or("", |stage| stage.entry_point),
+                            i
+                        );
                     }
                 }
             }

wgpu-core/src/pipeline.rs

@@ -280,8 +280,6 @@ pub struct RenderPipelineDescriptor<'a> {
 
 #[derive(Clone, Debug, Error)]
 pub enum ColorStateError {
-    #[error("output is missing")]
-    Missing,
     #[error("format {0:?} is not renderable")]
     FormatNotRenderable(wgt::TextureFormat),
     #[error("format {0:?} is not blendable")]
@@ -317,8 +315,6 @@ pub enum CreateRenderPipelineError {
     Device(#[from] DeviceError),
     #[error("pipeline layout is invalid")]
     InvalidLayout,
-    #[error("fragment output @location({0}) is invalid")]
-    InvalidFragmentOutputLocation(u32),
     #[error("unable to derive an implicit layout")]
     Implicit(#[from] ImplicitLayoutError),
     #[error("color state [{0}] is invalid")]