Bug 1637605 - Add support for polymorphic return values to ToResultInvoke. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D75294

mfbt/tests/gtest/TestResultExtensions.cpp

@@ -7,6 +7,7 @@
 #include "gtest/gtest.h"
 
 #include "mozilla/ResultExtensions.h"
+#include "nsLocalFile.h"
 
 #include <functional>
 
@@ -47,6 +48,12 @@ class TestClass {
 
   nsresult NonOverloadedNoOutput(int aIn) { return NS_OK; }
   nsresult NonOverloadedNoOutputFails(int aIn) { return NS_ERROR_FAILURE; }
+
+  nsresult PolymorphicNoInput(nsIFile** aOut) {
+    *aOut = MakeAndAddRef<nsLocalFile>().take();
+    return NS_OK;
+  }
+  nsresult PolymorphicNoInputFails(nsIFile** aOut) { return NS_ERROR_FAILURE; }
 };
 }  // namespace
 
@@ -205,3 +212,35 @@ TEST(ResultExtensions_ToResultInvoke, MemberFunction_NoOutput)
     ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
   }
 }
+
+TEST(ResultExtensions_ToResultInvoke, PolymorphicPointerResult_nsCOMPtr_Result)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = ToResultInvoke<nsCOMPtr<nsIFile>>(
+        std::mem_fn(&TestClass::PolymorphicNoInput), foo);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<nsCOMPtr<nsIFile>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_NE(nullptr, valOrErr.inspect());
+
+    ASSERT_EQ(ToResultInvoke<nsString>(std::mem_fn(&nsIFile::GetPath),
+                                       *MakeRefPtr<nsLocalFile>())
+                  .inspect(),
+              ToResultInvoke<nsString>(std::mem_fn(&nsIFile::GetPath),
+                                       valOrErr.inspect())
+                  .inspect());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvoke<nsCOMPtr<nsIFile>>(
+        std::mem_fn(&TestClass::PolymorphicNoInputFails), foo);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<nsCOMPtr<nsIFile>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}

xpcom/base/nsCOMPtr.h

@@ -1507,4 +1507,20 @@ RefPtr<T> ToRefPtr(nsCOMPtr<T>&& aObj) {
   return aObj.forget();
 }
 
+// Integration with ResultExtensions.h
+template <typename R>
+auto ResultRefAsParam(nsCOMPtr<R>& aResult) {
+  return getter_AddRefs(aResult);
+}
+
+namespace mozilla::detail {
+template <typename T>
+struct outparam_as_pointer;
+
+template <typename T>
+struct outparam_as_pointer<nsGetterAddRefs<T>> {
+  using type = T**;
+};
+}  // namespace mozilla::detail
+
 #endif  // !defined(nsCOMPtr_h___)