Bug 1659680 - QM: Introduce ToResultGet and use it in EnsureStorageIsInitialized; r=dom-workers-and-storage-reviewers,sg

Differential Revision: https://phabricator.services.mozilla.com/D87422

dom/quota/ActorsParent.cpp

@@ -6426,15 +6426,9 @@ nsresult QuotaManager::EnsureStorageIsInitialized() {
     }
   }
 
-  // TODO: Convert to QM_TRY_VAR once we have an adapter for it.
-  nsCOMPtr<mozIStorageService> ss;
-  {
-    nsresult rv;
-    ss = do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
-    if (NS_WARN_IF(NS_FAILED(rv))) {
-      return rv;
-    }
-  }
+  QM_TRY_VAR(auto ss, ToResultGet<nsCOMPtr<mozIStorageService>>(
+                          MOZ_SELECT_OVERLOAD(do_GetService),
+                          MOZ_STORAGE_SERVICE_CONTRACTID));
 
   QM_TRY_VAR(auto connection,
              ToResultInvoke<nsCOMPtr<mozIStorageConnection>>(

dom/quota/QuotaCommon.h

@@ -21,6 +21,13 @@
 #define MOZ_REMOVE_PAREN_HELPER3(...) MOZ_REMOVE_PAREN_HELPER4_##__VA_ARGS__
 #define MOZ_REMOVE_PAREN_HELPER4_MOZ_REMOVE_PAREN_HELPER
 
+// See https://florianjw.de/en/passing_overloaded_functions.html
+// TODO: Add a test for this macro.
+#define MOZ_SELECT_OVERLOAD(func)                         \
+  [](auto&&... aArgs) -> decltype(auto) {                 \
+    return func(std::forward<decltype(aArgs)>(aArgs)...); \
+  }
+
 #define BEGIN_QUOTA_NAMESPACE \
   namespace mozilla {         \
   namespace dom {             \
@@ -447,6 +454,17 @@ auto ErrToOkOrErr(nsresult aValue) -> Result<V, nsresult> {
   return Err(aValue);
 }
 
+// TODO: Maybe move this to mfbt/ResultExtensions.h
+template <typename R, typename Func, typename... Args>
+Result<R, nsresult> ToResultGet(const Func& aFunc, Args&&... aArgs) {
+  nsresult rv;
+  R res = aFunc(std::forward<Args>(aArgs)..., &rv);
+  if (NS_FAILED(rv)) {
+    return Err(rv);
+  }
+  return res;
+}
+
 namespace dom {
 namespace quota {
 

dom/quota/test/gtest/TestQuotaCommon.cpp

@@ -379,3 +379,63 @@ TEST(QuotaCommon_ErrToOkOrErr, NsresultToNsCOMPtr_nullptr_Err)
   EXPECT_TRUE(res.isErr());
   EXPECT_EQ(res.unwrapErr(), NS_ERROR_UNEXPECTED);
 }
+
+TEST(QuotaCommon_ToResultGet, Lambda_NoInput)
+{
+  auto task = [](nsresult* aRv) -> int32_t {
+    *aRv = NS_OK;
+    return 42;
+  };
+
+  auto res = ToResultGet<int32_t>(task);
+
+  static_assert(std::is_same_v<decltype(res), Result<int32_t, nsresult>>);
+
+  EXPECT_TRUE(res.isOk());
+  EXPECT_EQ(res.unwrap(), 42);
+}
+
+TEST(QuotaCommon_ToResultGet, Lambda_NoInput_Err)
+{
+  auto task = [](nsresult* aRv) -> int32_t {
+    *aRv = NS_ERROR_FAILURE;
+    return -1;
+  };
+
+  auto res = ToResultGet<int32_t>(task);
+
+  static_assert(std::is_same_v<decltype(res), Result<int32_t, nsresult>>);
+
+  EXPECT_TRUE(res.isErr());
+  EXPECT_EQ(res.unwrapErr(), NS_ERROR_FAILURE);
+}
+
+TEST(QuotaCommon_ToResultGet, Lambda_WithInput)
+{
+  auto task = [](int32_t aValue, nsresult* aRv) -> int32_t {
+    *aRv = NS_OK;
+    return aValue * 2;
+  };
+
+  auto res = ToResultGet<int32_t>(task, 42);
+
+  static_assert(std::is_same_v<decltype(res), Result<int32_t, nsresult>>);
+
+  EXPECT_TRUE(res.isOk());
+  EXPECT_EQ(res.unwrap(), 84);
+}
+
+TEST(QuotaCommon_ToResultGet, Lambda_WithInput_Err)
+{
+  auto task = [](int32_t aValue, nsresult* aRv) -> int32_t {
+    *aRv = NS_ERROR_FAILURE;
+    return -1;
+  };
+
+  auto res = ToResultGet<int32_t>(task, 42);
+
+  static_assert(std::is_same_v<decltype(res), Result<int32_t, nsresult>>);
+
+  EXPECT_TRUE(res.isErr());
+  EXPECT_EQ(res.unwrapErr(), NS_ERROR_FAILURE);
+}