[wasm] Allow any return count for JSPI export

R=clemensb@chromium.org

Bug: v8:12191, v8:13231
Change-Id: I0104f54ce5cdc022f22800d4aeec68aac481219d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3856573Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82769}

src/wasm/wasm-js.cc

@@ -1920,14 +1920,14 @@ bool IsSuspendingSignature(const i::wasm::FunctionSig* inner_sig,
   return true;
 }
 
-// Given {inner_sig}: externref ti* -> to
-// {outer_sig} must be: ti* -> externref
+// Given {inner_sig}: externref [ti*] -> [to*]
+// {outer_sig} must be: [ti*] -> [externref]
 bool IsPromisingSignature(const i::wasm::FunctionSig* inner_sig,
                           const i::wasm::FunctionSig* outer_sig) {
   if (inner_sig->parameter_count() != outer_sig->parameter_count() + 1) {
     return false;
   }
-  if (inner_sig->return_count() != 1 || outer_sig->return_count() != 1) {
+  if (outer_sig->return_count() != 1) {
     return false;
   }
   if (inner_sig->GetParam(0) != i::wasm::kWasmExternRef) return false;

test/mjsunit/wasm/stack-switching.js

@@ -19,7 +19,6 @@ function ToPromising(wasm_export) {
   let sig = WebAssembly.Function.type(wasm_export);
   assertTrue(sig.parameters.length > 0);
   assertEquals('externref', sig.parameters[0]);
-  assertEquals(1, sig.results.length);
   let wrapper_sig = {
     parameters: sig.parameters.slice(1),
     results: ['externref']
@@ -466,3 +465,16 @@ function TestNestedSuspenders(suspend) {
   print(arguments.callee.name);
   TestNestedSuspenders(false);
 })();
+
+(function Regress13231() {
+  print(arguments.callee.name);
+  // Check that a promising function with no return is allowed.
+  let builder = new WasmModuleBuilder();
+  let sig_v_r = makeSig([kWasmExternRef], []);
+  builder.addFunction("export", sig_v_r).addBody([]).exportFunc();
+  let instance = builder.instantiate();
+  let export_wrapper = ToPromising(instance.exports.export);
+  let export_sig = WebAssembly.Function.type(export_wrapper);
+  assertEquals([], export_sig.parameters);
+  assertEquals(['externref'], export_sig.results);
+})();