Fix binary writing of strings without GC enabled (#5836)

2 files changed, 22 insertions, 4 deletions

diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 639f4b848..3ceab828b 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -1519,14 +1519,20 @@ void WasmBinaryWriter::writeType(Type type) {
 
 void WasmBinaryWriter::writeHeapType(HeapType type) {
   // ref.null always has a bottom heap type in Binaryen IR, but those types are
-  // only actually valid with GC enabled. When GC is not enabled, emit the
-  // corresponding valid top types instead.
+  // only actually valid with GC. Otherwise, emit the corresponding valid top
+  // types instead.
   if (!wasm->features.hasGC()) {
     if (HeapType::isSubType(type, HeapType::func)) {
       type = HeapType::func;
-    } else {
-      assert(HeapType::isSubType(type, HeapType::ext));
+    } else if (HeapType::isSubType(type, HeapType::ext)) {
       type = HeapType::ext;
+    } else if (wasm->features.hasStrings()) {
+      // Strings are enabled, and this isn't a func or an ext, so it must be a
+      // string type (string or stringview), which we'll emit below, or a bottom
+      // type (which we must allow, because we wouldn't know whether to emit a
+      // string or stringview for it).
+    } else {
+      WASM_UNREACHABLE("invalid type without GC");
     }
   }
 
diff --git a/test/lit/binary/strings-nogc.test b/test/lit/binary/strings-nogc.test
new file mode 100644
index 000000000..7aa21d750
--- /dev/null
+++ b/test/lit/binary/strings-nogc.test
@@ -0,0 +1,12 @@
+;; Verify that we support strings in the binary format even without GC.
+
+;; RUN: wasm-opt --enable-reference-types  --enable-strings --roundtrip %s
+
+(module
+ (func $0
+  (local $0 stringref)
+  (local.set $0
+   (ref.null none)
+  )
+ )
+)