4 files changed, 62 insertions, 7 deletions

diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 3f76a4421..9f298662b 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -430,7 +430,9 @@ enum Subsection {
   NameMemory = 6,
   NameGlobal = 7,
   NameElem = 8,
-  NameData = 9
+  NameData = 9,
+  // see: https://github.com/WebAssembly/gc/issues/193
+  NameField = 10
 };
 
 } // namespace UserSections
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index c0d7ab36e..c7096b154 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -795,6 +795,34 @@ void WasmBinaryWriter::writeNames() {
   // TODO: label, type, and element names
   // see: https://github.com/WebAssembly/extended-name-section
 
+  // GC field names
+  if (wasm->features.hasGC()) {
+    std::vector<HeapType> relevantTypes;
+    for (auto& type : types) {
+      if (type.isStruct() && wasm->typeNames.count(type) &&
+          !wasm->typeNames.at(type).fieldNames.empty()) {
+        relevantTypes.push_back(type);
+      }
+    }
+    if (!relevantTypes.empty()) {
+      auto substart =
+        startSubsection(BinaryConsts::UserSections::Subsection::NameField);
+      o << U32LEB(relevantTypes.size());
+      for (Index i = 0; i < relevantTypes.size(); i++) {
+        auto type = relevantTypes[i];
+        o << U32LEB(typeIndices[type]);
+        std::unordered_map<Index, Name>& fieldNames =
+          wasm->typeNames.at(type).fieldNames;
+        o << U32LEB(fieldNames.size());
+        for (auto& kv : fieldNames) {
+          o << U32LEB(kv.first);
+          writeEscapedName(kv.second.str);
+        }
+      }
+      finishSubsection(substart);
+    }
+  }
+
   finishSection(start);
 }
 
@@ -2908,6 +2936,26 @@ void WasmBinaryBuilder::readNames(size_t payloadLen) {
                     << std::to_string(index) << std::endl;
         }
       }
+    } else if (nameType == BinaryConsts::UserSections::Subsection::NameField) {
+      auto numTypes = getU32LEB();
+      for (size_t i = 0; i < numTypes; i++) {
+        auto typeIndex = getU32LEB();
+        bool validType =
+          typeIndex < types.size() && types[typeIndex].isStruct();
+        if (!validType) {
+          std::cerr << "warning: invalid field index in name field section\n";
+        }
+        auto numFields = getU32LEB();
+        NameProcessor processor;
+        for (size_t i = 0; i < numFields; i++) {
+          auto fieldIndex = getU32LEB();
+          auto rawName = getInlineString();
+          auto name = processor.process(rawName);
+          if (validType) {
+            wasm.typeNames[types[typeIndex]].fieldNames[fieldIndex] = name;
+          }
+        }
+      }
     } else {
       std::cerr << "warning: unknown name subsection with id "
                 << std::to_string(nameType) << " at " << pos << std::endl;
diff --git a/src/wasm/wasm-s-parser.cpp b/src/wasm/wasm-s-parser.cpp
index 15b9cd5cb..1271ff603 100644
--- a/src/wasm/wasm-s-parser.cpp
+++ b/src/wasm/wasm-s-parser.cpp
@@ -826,7 +826,12 @@ void SExpressionWasmBuilder::preParseHeapTypes(Element& module) {
   auto parseStructDef = [&](Element& elem, size_t typeIndex) {
     FieldList fields;
     for (Index i = 1; i < elem.size(); i++) {
-      fields.emplace_back(parseField(elem[i], fieldNames[typeIndex][i - 1]));
+      Name name;
+      fields.emplace_back(parseField(elem[i], name));
+      if (name.is()) {
+        // Only add the name to the map if it exists.
+        fieldNames[typeIndex][i - 1] = name;
+      }
     }
     return Struct(fields);
   };
diff --git a/test/heap-types.wast.fromBinary b/test/heap-types.wast.fromBinary
index 75dcae823..2fe6adbe1 100644
--- a/test/heap-types.wast.fromBinary
+++ b/test/heap-types.wast.fromBinary
@@ -1,11 +1,11 @@
 (module
- (type $struct.A (struct (field i32) (field f32) (field f64)))
+ (type $struct.A (struct (field i32) (field f32) (field $named f64)))
  (type $struct.B (struct (field i8) (field (mut i16)) (field (ref null $struct.A)) (field (mut (ref null $struct.A)))))
  (type $matrix (array (ref null $vector)))
  (type $vector (array (mut f64)))
  (type $anyref_=>_none (func (param anyref)))
  (type $parent (struct ))
- (type $struct.C (struct (field (mut f32))))
+ (type $struct.C (struct (field $named-mut (mut f32))))
  (type $none_=>_none (func))
  (type $rtt_1_$parent_=>_none (func (param (rtt 1 $parent))))
  (type $rtt_$parent_=>_none (func (param (rtt $parent))))
@@ -42,12 +42,12 @@
    )
   )
   (drop
-   (struct.get $struct.A 2
+   (struct.get $struct.A $named
     (local.get $x)
    )
   )
   (drop
-   (struct.get $struct.A 2
+   (struct.get $struct.A $named
     (local.get $x)
    )
   )
@@ -88,7 +88,7 @@
     (i32.const 1)
    )
   )
-  (struct.set $struct.C 0
+  (struct.set $struct.C $named-mut
    (ref.null $struct.C)
    (f32.const 100)
   )