Add initial support for anyref as an opaque type (#2294)

Another round of trying to push upstream things from my fork.

This PR only adds support for anyref itself as an opaque type. It does NOT implement the full [reference types proposal](https://github.com/WebAssembly/reference-types/blob/master/proposals/reference-types/Overview.md)--so no table.get/set/grow/etc or ref.null, ref.func, etc.

Figured it was easier to review and merge as we go, especially if I did something fundamentally wrong.

***

I did put it under the `--enable-reference-types` flag as I imagine that even though this PR doesn't complete the full feature set, it probably is the right home. Lmk if not.

I'll also be adding a few github comments to places I want to point out/question.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 1efa24b48..d01502e9b 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -381,7 +381,9 @@ enum EncodedType {
   v128 = -0x5, // 0x7b
   // elem_type
   AnyFunc = -0x10, // 0x70
-  // reference type
+  // opaque reference type
+  anyref = -0x11, // 0x6f
+  // exception reference type
   exnref = -0x18, // 0x68
   // func_type form
   Func = -0x20, // 0x60
@@ -406,6 +408,7 @@ extern const char* SignExtFeature;
 extern const char* SIMD128Feature;
 extern const char* ExceptionHandlingFeature;
 extern const char* TailCallFeature;
+extern const char* ReferenceTypesFeature;
 
 enum Subsection {
   NameFunction = 1,
@@ -903,6 +906,9 @@ inline S32LEB binaryType(Type type) {
     case v128:
       ret = BinaryConsts::EncodedType::v128;
       break;
+    case anyref:
+      ret = BinaryConsts::EncodedType::anyref;
+      break;
     case exnref:
       ret = BinaryConsts::EncodedType::exnref;
       break;