Don't panic on empty core rec groups in components

crates/environ/src/component/translate.rs

@@ -14,8 +14,8 @@ use indexmap::IndexMap;
 use std::collections::{HashMap, HashSet};
 use std::mem;
 use wasmparser::component_types::{
-    AliasableResourceId, ComponentCoreModuleTypeId, ComponentDefinedTypeId, ComponentEntityType,
-    ComponentFuncTypeId, ComponentInstanceTypeId, ComponentValType,
+    AliasableResourceId, ComponentCoreModuleTypeId, ComponentCoreTypeId, ComponentDefinedTypeId,
+    ComponentEntityType, ComponentFuncTypeId, ComponentInstanceTypeId, ComponentValType,
 };
 use wasmparser::types::Types;
 use wasmparser::{Chunk, ComponentExternName, Encoding, Parser, Payload, Validator};
@@ -903,17 +903,21 @@ impl<'a, 'data> Translator<'a, 'data> {
                     .core_type_count_in_component();
                 self.validator.core_type_section(&s)?;
                 let types = self.validator.types(0).unwrap();
-                for ty in s {
-                    match ty? {
-                        wasmparser::CoreType::Rec(group) => {
-                            let id = types.core_type_at_in_component(index).unwrap_sub();
+                let count = types.core_type_count_in_component();
+                while index < count {
+                    match types.core_type_at_in_component(index) {
+                        // The current type index is always the first type of
+                        // its rec group, so intern the group and then skip
+                        // past the rest of its types.
+                        ComponentCoreTypeId::Sub(id) => {
                             let group_id = types.rec_group_id_of(id);
                             self.types
                                 .module_types_builder()
                                 .intern_rec_group(types, group_id)?;
-                            index += u32::try_from(group.types().len()).unwrap();
+                            index +=
+                                u32::try_from(types.rec_group_elements(group_id).len()).unwrap();
                         }
-                        wasmparser::CoreType::Module(_) => index += 1,
+                        ComponentCoreTypeId::Module(_) => index += 1,
                     }
                 }
             }

tests/misc_testsuite/component-model/empty-rec-groups.wast

@@ -0,0 +1,6 @@
+;;! gc = true
+
+;; Empty core rec groups define no types.
+(component (core rec))
+(component (core rec) (core type (module)))
+(component (core type (sub (array i8))) (core rec))