Fix validation errors for struct.wait (#8394)

Prior to #8378, any `assert_invalid` assertions that required a feature
to be enabled spuriously succeeded even if the test would otherwise
wrongly pass validation. The checks that were in wasm-validator.cpp
didn't run if the ref was null or unreachable, which is wrong because
the type + field index immediates could still be wrong.

Move these assertions to IRBuilder where we have the type immediate
available.

Verified by removing the assert_invalid parts and checking that the
error message matches what's in the test.

Part of #8315.

src/wasm/wasm-ir-builder.cpp

diff --git a/src/wasm/wasm-ir-builder.cpp b/src/wasm/wasm-ir-builder.cpp
index 7cc87a0..1e7463e 100644
--- a/src/wasm/wasm-ir-builder.cpp
+++ b/src/wasm/wasm-ir-builder.cpp
@@ -2250,6 +2250,16 @@
   if (!type.isStruct()) {
     return Err{"expected struct type annotation on struct.wait"};
   }
+  // This is likely checked in the caller by the `fieldidx` parser.
+  if (index >= type.getStruct().fields.size()) {
+    return Err{"struct.wait field index out of bounds"};
+  }
+
+  if (type.getStruct().fields.at(index).packedType !=
+      Field::PackedType::WaitQueue) {
+    return Err{"struct.wait field index must contain a `waitqueue`"};
+  }
+
   StructWait curr(wasm.allocator);
   curr.index = index;
   CHECK_ERR(ChildPopper{*this}.visitStructWait(&curr, type));

src/wasm/wasm-validator.cpp

diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index f79c96a..ae862a3 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -3517,25 +3517,12 @@
                 curr,
                 "struct.wait timeout must be an i64");
 
-  if (curr->ref->type == Type::unreachable || curr->ref->type.isNull()) {
-    return;
-  }
-
-  // In practice this likely fails during parsing instead.
-  if (!shouldBeTrue(curr->index <
-                      curr->ref->type.getHeapType().getStruct().fields.size(),
-                    curr,
-                    "struct.wait index immediate should be less than the field "
-                    "count of the struct")) {
-    return;
-  }
-
-  shouldBeTrue(curr->ref->type.getHeapType()
-                   .getStruct()
-                   .fields.at(curr->index)
-                   .packedType == Field::WaitQueue,
-               curr,
-               "struct.wait struct field must be a waitqueue");
+  // Checks to the ref argument's type are done in IRBuilder where we have the
+  // type annotation immediate available. We check that
+  // * The reference arg is a subtype of the type immediate
+  // * The index immediate is a valid field index of the type immediate (and
+  // thus valid for the reference's type too)
+  // * The index points to a packed waitqueue field
 }
 
 void FunctionValidator::visitArrayNew(ArrayNew* curr) {

test/spec/waitqueue.wast

diff --git a/test/spec/waitqueue.wast b/test/spec/waitqueue.wast
index 7383d4e..8e83708 100644
--- a/test/spec/waitqueue.wast
+++ b/test/spec/waitqueue.wast
@@ -4,7 +4,7 @@
     (func (param $expected i32) (param $timeout i64) (result i32)
       (struct.wait $t 0 (ref.null $t) (local.get $expected) (local.get $timeout))
     )
-  ) "struct.wait struct field must be a waitqueue"
+  ) "struct.wait struct field index must contain a `waitqueue`"
 )
 
 (assert_invalid
@@ -38,7 +38,7 @@
 
 ;; unreachable is allowed
 (module
-  (type $t (struct (field i32)))
+  (type $t (struct (field waitqueue)))
   (func (param $expected i32) (param $timeout i64) (result i32)
     (struct.wait $t 0 (unreachable) (local.get $expected) (local.get $timeout))
   )