[wasm-gc] Fix i31ref decoding and some error messages

Bug: v8:7748
Change-Id: I4d6aef3ab503ffc9b9624b6d65d74f36141d550d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2403258
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69880}

src/wasm/function-body-decoder-impl.h

@@ -211,7 +211,8 @@ ValueType read_value_type(Decoder* decoder, const byte* pc,
     case kLocalExternRef:
     case kLocalI31Ref: {
       HeapType heap_type = HeapType::from_code(code);
-      ValueType result = ValueType::Ref(heap_type, kNullable);
+      ValueType result = ValueType::Ref(
+          heap_type, code == kLocalI31Ref ? kNonNullable : kNullable);
       if (!VALIDATE(enabled.contains(feature_for_heap_type(heap_type)))) {
         decoder->errorf(
             pc, "invalid value type '%s', enable with --experimental-wasm-%s",
@@ -234,7 +235,7 @@ ValueType read_value_type(Decoder* decoder, const byte* pc,
       Nullability nullability = code == kLocalOptRef ? kNullable : kNonNullable;
       if (!VALIDATE(enabled.has_typed_funcref())) {
         decoder->errorf(pc,
-                        "Invalid type 'ref%s', enable with "
+                        "Invalid type '(ref%s <heaptype>)', enable with "
                         "--experimental-wasm-typed-funcref",
                         nullability == kNullable ? " null" : "");
         return kWasmBottom;

src/wasm/module-decoder.cc

@@ -561,7 +561,9 @@ class ModuleDecoderImpl : public Decoder {
         }
         case kWasmStructTypeCode: {
           if (!enabled_features_.has_gc()) {
-            errorf(pc(), "struct types are part of the GC proposal");
+            errorf(pc(),
+                   "invalid struct type definition, enable with "
+                   "--experimental-wasm-gc");
             break;
           }
           const StructType* s = consume_struct(module_->signature_zone.get());
@@ -572,7 +574,9 @@ class ModuleDecoderImpl : public Decoder {
         }
         case kWasmArrayTypeCode: {
           if (!enabled_features_.has_gc()) {
-            errorf(pc(), "array types are part of the GC proposal");
+            errorf(pc(),
+                   "invalid array type definition, enable with "
+                   "--experimental-wasm-gc");
             break;
           }
           const ArrayType* type = consume_array(module_->signature_zone.get());