Add utility function for setting constants map

wgpu/src/backend/webgpu.rs

@@ -1875,10 +1875,9 @@ impl crate::context::Context for ContextWebGpu {
         let module: &<ContextWebGpu as crate::Context>::ShaderModuleData =
             downcast_ref(desc.vertex.module.data.as_ref());
         let mut mapped_vertex_state = webgpu_sys::GpuVertexState::new(&module.0.module);
-        let _ = js_sys::Reflect::set(
+        insert_constants_map(
             &mapped_vertex_state,
-            &"constants".into(),
-            &hashmap_to_jsvalue(desc.vertex.compilation_options.constants),
+            desc.vertex.compilation_options.constants,
         );
         mapped_vertex_state.entry_point(desc.vertex.entry_point);
 
@@ -1956,11 +1955,7 @@ impl crate::context::Context for ContextWebGpu {
                 downcast_ref(frag.module.data.as_ref());
             let mut mapped_fragment_desc =
                 webgpu_sys::GpuFragmentState::new(&module.0.module, &targets);
-            let _ = js_sys::Reflect::set(
-                &mapped_fragment_desc,
-                &"constants".into(),
-                &hashmap_to_jsvalue(frag.compilation_options.constants),
-            );
+            insert_constants_map(&mapped_vertex_state, frag.compilation_options.constants);
             mapped_fragment_desc.entry_point(frag.entry_point);
             mapped_desc.fragment(&mapped_fragment_desc);
         }
@@ -1987,11 +1982,7 @@ impl crate::context::Context for ContextWebGpu {
             downcast_ref(desc.module.data.as_ref());
         let mut mapped_compute_stage =
             webgpu_sys::GpuProgrammableStage::new(&shader_module.0.module);
-        let _ = js_sys::Reflect::set(
-            &mapped_compute_stage,
-            &"constants".into(),
-            &hashmap_to_jsvalue(desc.compilation_options.constants),
-        );
+        insert_constants_map(&mapped_compute_stage, desc.compilation_options.constants);
         mapped_compute_stage.entry_point(desc.entry_point);
         let auto_layout = wasm_bindgen::JsValue::from(webgpu_sys::GpuAutoLayoutMode::Auto);
         let mut mapped_desc = webgpu_sys::GpuComputePipelineDescriptor::new(
@@ -3826,12 +3817,30 @@ impl Drop for BufferMappedRange {
     }
 }
 
+/// Adds the constants map to the given pipeline descriptor if the map is nonempty.
+/// Logs an error if the map cannot be set.
+///
+/// This function is necessary because the constants array is not currently
+/// exposed by `wasm-bindgen`. See the following issues for details:
+/// - [gfx-rs/wgpu#5688](https://github.com/gfx-rs/wgpu/pull/5688)
+/// - [rustwasm/wasm-bindgen#3587](https://github.com/rustwasm/wasm-bindgen/issues/3587)
+fn insert_constants_map(target: &JsValue, map: &HashMap<String, f64>) {
+    if !map.is_empty() {
+        let result = js_sys::Reflect::set(target, &"constants".into(), &hashmap_to_jsvalue(map));
+
+        if let Err(error) = result {
+            log::error!("Failed to set constants map for pipeline: {error:?}");
+        }
+    }
+}
+
 /// Converts a hashmap to a Javascript object.
 fn hashmap_to_jsvalue(map: &HashMap<String, f64>) -> JsValue {
     let obj = js_sys::Object::new();
 
     for (k, v) in map.iter() {
-        let _ = js_sys::Reflect::set(&obj, &k.into(), &(*v).into());
+        js_sys::Reflect::set(&obj, &k.into(), &(*v).into())
+            .expect("Setting the values in a Javascript map should never fail");
     }
 
     JsValue::from(obj)