Fix double decoration if a binding array contains a struct with a runtime array (#5776)

CHANGELOG.md

@@ -170,6 +170,10 @@ By @atlv24 in [#5383](https://github.com/gfx-rs/wgpu/pull/5383)
 
 - Added support for pipeline-overridable constants to the WebGPU backend by @DouglasDwyer in [#5688](https://github.com/gfx-rs/wgpu/pull/5688)
 
+#### Naga
+
+- In spv-out don't decorate a `BindingArray`'s type with `Block` if the type is a struct with a runtime array by @Vecvec in [#5776](https://github.com/gfx-rs/wgpu/pull/5776)
+
 ## v0.20.0 (2024-04-28)
 
 ### Major Changes

naga/src/back/spv/writer.rs

@@ -1763,8 +1763,27 @@ impl Writer {
             if let crate::AddressSpace::Storage { .. } = global_variable.space {
                 match ir_module.types[global_variable.ty].inner {
                     crate::TypeInner::BindingArray { base, .. } => {
-                        let decorated_id = self.get_type_id(LookupType::Handle(base));
-                        self.decorate(decorated_id, Decoration::Block, &[]);
+                        let ty = &ir_module.types[base];
+                        let mut should_decorate = true;
+                        // Check if the type has a runtime array.
+                        // A normal runtime array gets validated out,
+                        // so only structs can be with runtime arrays
+                        if let crate::TypeInner::Struct { ref members, .. } = ty.inner {
+                            // only the last member in a struct can be dynamically sized
+                            if let Some(last_member) = members.last() {
+                                if let &crate::TypeInner::Array {
+                                    size: crate::ArraySize::Dynamic,
+                                    ..
+                                } = &ir_module.types[last_member.ty].inner
+                                {
+                                    should_decorate = false;
+                                }
+                            }
+                        }
+                        if should_decorate {
+                            let decorated_id = self.get_type_id(LookupType::Handle(base));
+                            self.decorate(decorated_id, Decoration::Block, &[]);
+                        }
                     }
                     _ => (),
                 };

naga/tests/out/spv/binding-buffer-arrays.spvasm

@@ -19,7 +19,6 @@ OpMemberDecorate %10 0 Offset 0
 OpDecorate %11 NonWritable
 OpDecorate %11 DescriptorSet 0
 OpDecorate %11 Binding 0
-OpDecorate %7 Block
 OpDecorate %15 DescriptorSet 0
 OpDecorate %15 Binding 10
 OpDecorate %16 Block