Add support for ref.null constant in WAST expectations (#8076)

Fixes `ref_null.wast` spec test and partially fixes `ref_is_null.wast`
and `select.wast`.

Author: stevenfontanella

scripts/test/shared.py

@@ -455,10 +455,9 @@ def get_tests(test_dir, extensions=[], recursive=False):
     'try_table.wast',  # Requires try_table interpretation
     'local_init.wast',  # Requires local validation to respect unnamed blocks
     'ref_func.wast',   # Requires rejecting undeclared functions references
-    'ref_is_null.wast',  # Requires ref.null wast constants
-    'ref_null.wast',     # Requires ref.null wast constants
+    'ref_is_null.wast',  # Requires support for non-nullable reference types in tables
     'return_call_indirect.wast',  # Requires more precise unreachable validation
-    'select.wast',  # Requires ref.null wast constants
+    'select.wast',  # Missing validation of type annotation on select
     'table.wast',  # Requires support for table default elements
     'unreached-invalid.wast',  # Requires more precise unreachable validation
     'array.wast',  # Requires support for table default elements

src/parser/wast-parser.cpp

@@ -213,6 +213,13 @@ Result<ExpectedResult> result(Lexer& in) {
     return lanes;
   }
 
+  if (in.takeSExprStart("ref.null")) {
+    if (!in.takeRParen()) {
+      return in.err("expected end of ref.null");
+    }
+    return NullRefResult{};
+  }
+
   if (in.takeSExprStart("ref.extern")) {
     if (!in.takeRParen()) {
       return in.err("expected end of ref.extern");

src/parser/wat-parser.h

@@ -63,6 +63,8 @@ struct RefResult {
   HeapType type;
 };
 
+struct NullRefResult {};
+
 enum class NaNKind { Canonical, Arithmetic };
 
 struct NaNResult {
@@ -74,7 +76,8 @@ using LaneResult = std::variant<Literal, NaNResult>;
 
 using LaneResults = std::vector<LaneResult>;
 
-using ExpectedResult = std::variant<Literal, RefResult, NaNResult, LaneResults>;
+using ExpectedResult =
+  std::variant<Literal, NullRefResult, RefResult, NaNResult, LaneResults>;
 
 using ExpectedResults = std::vector<ExpectedResult>;
 

src/tools/wasm-shell.cpp

@@ -342,6 +342,12 @@ struct Shell {
               << atIndex();
           return Err{err.str()};
         }
+      } else if ([[maybe_unused]] auto* nullRef =
+                   std::get_if<NullRefResult>(&expected)) {
+        if (!val.isNull()) {
+          err << "expected ref.null, got " << val << atIndex();
+          return Err{err.str()};
+        }
       } else if (auto* nan = std::get_if<NaNResult>(&expected)) {
         auto check = checkNaN(val, *nan);
         if (auto* e = check.getErr()) {