Validate RefAsNonNull (#6785)

Fixes #6781

src/wasm/wasm-validator.cpp

@@ -2230,10 +2230,19 @@ void FunctionValidator::visitRefIsNull(RefIsNull* curr) {
 }
 
 void FunctionValidator::visitRefAs(RefAs* curr) {
+  if (curr->value->type != Type::unreachable &&
+      !shouldBeTrue(
+        curr->value->type.isRef(), curr, "ref.as value must be reference")) {
+    return;
+  }
   switch (curr->op) {
-    default:
-      // TODO: validate all the other ref.as_*
+    case RefAsNonNull: {
+      shouldBeTrue(
+        getModule()->features.hasReferenceTypes(),
+        curr,
+        "ref.as requires reference-types [--enable-reference-types]");
       break;
+    }
     case AnyConvertExtern: {
       shouldBeTrue(getModule()->features.hasGC(),
                    curr,

src/wasm/wasm.cpp

@@ -1223,7 +1223,13 @@ void ArrayInitElem::finalize() {
 }
 
 void RefAs::finalize() {
-  if (value->type == Type::unreachable) {
+  // An unreachable child means we are unreachable. Also set ourselves to
+  // unreachable when the child is invalid (say, it is an i32 or some other non-
+  // reference), which avoids getHeapType() erroring right after us (in this
+  // situation, the validator will report an error later).
+  // TODO: Remove that part when we solve the validation issue more generally,
+  //       see https://github.com/WebAssembly/binaryen/issues/6781
+  if (!value->type.isRef()) {
     type = Type::unreachable;
     return;
   }

test/lit/validation/non-ref.wast

@@ -0,0 +1,13 @@
+;; RUN: not wasm-opt %s -all 2>&1 | filecheck %s
+
+;; CHECK: ref.as value must be reference
+
+(module
+  (func $test
+    (drop
+      (ref.as_non_null
+        (i32.const 42)
+      )
+    )
+  )
+)