1 files changed, 73 insertions, 0 deletions
diff --git a/js/src/tests/non262/ShadowRealms/function-return.js b/js/src/tests/non262/ShadowRealms/function-return.js
new file mode 100644
index 0000000000..d0853bcbb3
--- /dev/null
+++ b/js/src/tests/non262/ShadowRealms/function-return.js
@@ -0,0 +1,73 @@
+// |reftest| shell-option(--enable-shadow-realms) skip-if(!xulRuntime.shell)
+
+// The output of Function.prototype.toString must match the |NativeFunction| production.
+// https://tc39.es/ecma262/#sec-function.prototype.tostring
+//
+// NativeFunction :
+//   function NativeFunctionAccessor? PropertyName[~Yield, ~Await]? ( FormalParameters[~Yield, ~Await] ) { [ native code ] }
+//
+// NativeFunctionAccessor :
+//   get
+//   set
+
+function assertMatchesNativeFunction(f) {
+  var source = f.toString();
+
+  // Starts with "function".
+  assertEq(/^function\b/.test(source), true);
+
+  // Remove the optional |NativeFunctionAccessor| part.
+  var nativeAccesorRe = /^(?<start>\s*function)(?<accessor>\s+[gs]et)(?<end>\s+[^(].*)$/;
+  var match = nativeAccesorRe.exec(source);
+  if (match) {
+    source = match.groups.start + match.groups.end;
+  }
+
+  // The body must include the string "[native code".
+  var closeCurly = source.lastIndexOf("}");
+  var openCurly = source.lastIndexOf("{");
+  assertEq(openCurly < closeCurly, true);
+
+  var body = source.slice(openCurly + 1, closeCurly);
+  assertEq(/^\s*\[native code\]\s*$/.test(body), true);
+
+  // Verify |PropertyName| and |FormalParameters| are syntactically correct by parsing the source
+  // code. But we first need to replace the "[native code]" substring.
+  source = source.slice(0, openCurly) + "{}";
+
+  // Also prepend "void" to parse the function source code as a FunctionExpression, because we
+  // don't necessarily have a name part.
+  source = "void " + source;
+
+  try {
+    Function(source);
+  } catch {
+    assertEq(true, false, `${source} doesn't match NativeFunction`);
+  }
+}
+
+let sr = new ShadowRealm();
+var f = sr.evaluate("function f() { }; f");
+
+assertMatchesNativeFunction(f);
+
+f.name = "koala"
+assertMatchesNativeFunction(f);
+
+Object.defineProperty(f, "name", { writable: true, value: "koala" });
+assertMatchesNativeFunction(f);
+
+f.name = "panda"
+assertMatchesNativeFunction(f);
+
+f.name = "has whitespace, therefore shouldn't match the PropertyName production";
+assertMatchesNativeFunction(f);
+
+f.name = 123;
+assertMatchesNativeFunction(f);
+
+Object.defineProperty(f, "name", { get() { throw new Error("unexpected side-effect"); } });
+assertMatchesNativeFunction(f);
+
+if (typeof reportCompare === 'function')
+    reportCompare(true, true);