2 files changed, 44 insertions, 9 deletions
diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 62c2f7af2..12deeacab 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -382,6 +382,10 @@ enum EncodedType {
   Struct = -0x21, // 0x5f
   Array = -0x22,  // 0x5e
   Sub = -0x30,    // 0x50
+  // prototype nominal forms we still parse
+  FuncSubtype = -0x23,   // 0x5d
+  StructSubtype = -0x24, // 0x5c
+  ArraySubtype = -0x25,  // 0x5b
   // isorecursive recursion groups
   Rec = -0x31, // 0x4f
   // block_type
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 9dcdbb73d..60a4bad77 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -1985,6 +1985,7 @@ void WasmBinaryBuilder::readTypes() {
       builder.createRecGroup(i, groupSize);
       form = getS32LEB();
     }
+    std::optional<uint32_t> superIndex;
     if (form == BinaryConsts::EncodedType::Sub) {
       uint32_t supers = getU32LEB();
       if (supers > 0) {
@@ -1992,24 +1993,54 @@ void WasmBinaryBuilder::readTypes() {
           throwError("Invalid type definition with " + std::to_string(supers) +
                      " supertypes");
         }
-        uint32_t superIndex = getU32LEB();
-        if (superIndex > builder.size()) {
-          throwError("Out of bounds supertype index " +
-                     std::to_string(superIndex));
-        }
-        builder[i].subTypeOf(builder[superIndex]);
+        superIndex = getU32LEB();
       }
       form = getS32LEB();
     }
-    if (form == BinaryConsts::EncodedType::Func) {
+    if (form == BinaryConsts::EncodedType::Func ||
+        form == BinaryConsts::EncodedType::FuncSubtype) {
       builder[i] = readSignatureDef();
-    } else if (form == BinaryConsts::EncodedType::Struct) {
+    } else if (form == BinaryConsts::EncodedType::Struct ||
+               form == BinaryConsts::EncodedType::StructSubtype) {
       builder[i] = readStructDef();
-    } else if (form == BinaryConsts::EncodedType::Array) {
+    } else if (form == BinaryConsts::EncodedType::Array ||
+               form == BinaryConsts::EncodedType::ArraySubtype) {
       builder[i] = Array(readFieldDef());
     } else {
       throwError("Bad type form " + std::to_string(form));
     }
+    if (form == BinaryConsts::EncodedType::FuncSubtype ||
+        form == BinaryConsts::EncodedType::StructSubtype ||
+        form == BinaryConsts::EncodedType::ArraySubtype) {
+      int64_t super = getS64LEB(); // TODO: Actually s33
+      if (super >= 0) {
+        superIndex = (uint32_t)super;
+      } else {
+        // Validate but otherwise ignore trivial supertypes.
+        HeapType basicSuper;
+        if (!getBasicHeapType(super, basicSuper)) {
+          throwError("Unrecognized supertype " + std::to_string(super));
+        }
+        if (form == BinaryConsts::EncodedType::FuncSubtype) {
+          if (basicSuper != HeapType::func) {
+            throwError(
+              "The only allowed trivial supertype for functions is func");
+          }
+        } else {
+          if (basicSuper != HeapType::data) {
+            throwError("The only allowed trivial supertype for structs and "
+                       "arrays is data");
+          }
+        }
+      }
+    }
+    if (superIndex) {
+      if (*superIndex > builder.size()) {
+        throwError("Out of bounds supertype index " +
+                   std::to_string(*superIndex));
+      }
+      builder[i].subTypeOf(builder[*superIndex]);
+    }
   }
 
   auto result = builder.build();