[RT] Support expressions in element segments (#3666)

This PR adds support for `ref.null t` as a valid element segment
item. The abbreviated format of `(elem ... func $f $g...)` is kept in
both printing and binary emitting if all items are `ref.func`s. Public
APIs aren't updated in this PR.

1 files changed, 27 insertions, 7 deletions

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 4346fe705..6dfd495c0 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -2704,6 +2704,18 @@ struct PrintSExpression : public UnifiedExpressionVisitor<PrintSExpression> {
     if (curr->data.empty()) {
       return;
     }
+    bool allElementsRefFunc =
+      std::all_of(curr->data.begin(), curr->data.end(), [](Expression* entry) {
+        return entry->is<RefFunc>();
+      });
+    auto printElemType = [&]() {
+      if (allElementsRefFunc) {
+        TypeNamePrinter(o, currModule).print(HeapType::func);
+      } else {
+        TypeNamePrinter(o, currModule).print(Type::funcref);
+      }
+    };
+
     doIndent(o, indent);
     o << '(';
     printMedium(o, "elem");
@@ -2714,7 +2726,7 @@ struct PrintSExpression : public UnifiedExpressionVisitor<PrintSExpression> {
 
     if (curr->table.is()) {
       // TODO(reference-types): check for old-style based on the complete spec
-      if (currModule->tables.size() > 1) {
+      if (!allElementsRefFunc || currModule->tables.size() > 1) {
         // tableuse
         o << " (table ";
         printName(curr->table, o);
@@ -2724,18 +2736,26 @@ struct PrintSExpression : public UnifiedExpressionVisitor<PrintSExpression> {
       o << ' ';
       visit(curr->offset);
 
-      if (currModule->tables.size() > 1) {
+      if (!allElementsRefFunc || currModule->tables.size() > 1) {
         o << ' ';
-        TypeNamePrinter(o, currModule).print(HeapType::func);
+        printElemType();
       }
     } else {
       o << ' ';
-      TypeNamePrinter(o, currModule).print(HeapType::func);
+      printElemType();
     }
 
-    for (auto name : curr->data) {
-      o << ' ';
-      printName(name, o);
+    if (allElementsRefFunc) {
+      for (auto* entry : curr->data) {
+        auto* refFunc = entry->cast<RefFunc>();
+        o << ' ';
+        printName(refFunc->func, o);
+      }
+    } else {
+      for (auto* entry : curr->data) {
+        o << ' ';
+        printExpression(entry, o);
+      }
     }
     o << ')' << maybeNewLine;
   }