1 files changed, 158 insertions, 0 deletions
diff --git a/dom/indexedDB/IDBResult.h b/dom/indexedDB/IDBResult.h
new file mode 100644
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+++ b/dom/indexedDB/IDBResult.h
@@ -0,0 +1,158 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_indexeddb_idbresult_h__
+#define mozilla_dom_indexeddb_idbresult_h__
+
+#include "mozilla/ErrorResult.h"
+#include "mozilla/ResultVariant.h"
+#include "mozilla/Variant.h"
+
+#include <type_traits>
+#include <utility>
+
+namespace mozilla::dom::indexedDB {
+
+// IDBSpecialValue represents two special return values, distinct from any other
+// value, used in several places in the IndexedDB spec.
+enum class IDBSpecialValue {
+  Failure,
+  Invalid,
+};
+
+namespace detail {
+
+template <IDBSpecialValue Value>
+using SpecialConstant = std::integral_constant<IDBSpecialValue, Value>;
+using FailureType = SpecialConstant<IDBSpecialValue::Failure>;
+using InvalidType = SpecialConstant<IDBSpecialValue::Invalid>;
+struct ExceptionType final {};
+}  // namespace detail
+
+// Put these in a subnamespace to avoid conflicts from the combination of 1.
+// using namespace mozilla::dom::indexedDB; in cpp files, 2. the unified build
+// and 3. mozilla::dom::Exception
+namespace SpecialValues {
+constexpr const detail::FailureType Failure;
+constexpr const detail::InvalidType Invalid;
+constexpr const detail::ExceptionType Exception;
+}  // namespace SpecialValues
+
+namespace detail {
+template <IDBSpecialValue... Elements>
+struct IsSortedSet;
+
+template <IDBSpecialValue First, IDBSpecialValue Second,
+          IDBSpecialValue... Rest>
+struct IsSortedSet<First, Second, Rest...>
+    : std::integral_constant<bool, IsSortedSet<First, Second>::value &&
+                                       IsSortedSet<Second, Rest...>::value> {};
+
+template <IDBSpecialValue First, IDBSpecialValue Second>
+struct IsSortedSet<First, Second>
+    : std::integral_constant<bool, (First < Second)> {};
+
+template <IDBSpecialValue First>
+struct IsSortedSet<First> : std::true_type {};
+
+template <>
+struct IsSortedSet<> : std::true_type {};
+
+template <IDBSpecialValue... S>
+class IDBError {
+  // This assertion ensures that permutations of the set of possible special
+  // values don't create distinct types.
+  static_assert(IsSortedSet<S...>::value,
+                "special value list must be sorted and unique");
+
+  template <IDBSpecialValue... U>
+  friend class IDBError;
+
+ public:
+  MOZ_IMPLICIT IDBError(nsresult aRv) : mVariant(ErrorResult{aRv}) {}
+
+  IDBError(ExceptionType, ErrorResult&& aErrorResult)
+      : mVariant(std::move(aErrorResult)) {}
+
+  template <IDBSpecialValue Special>
+  MOZ_IMPLICIT IDBError(SpecialConstant<Special>)
+      : mVariant(SpecialConstant<Special>{}) {}
+
+  IDBError(IDBError&&) = default;
+  IDBError& operator=(IDBError&&) = default;
+
+  // Construct an IDBResult from another IDBResult whose set of possible special
+  // values is a subset of this one's.
+  template <IDBSpecialValue... U>
+  MOZ_IMPLICIT IDBError(IDBError<U...>&& aOther)
+      : mVariant(aOther.mVariant.match(
+            [](auto& aVariant) { return VariantType{std::move(aVariant)}; })) {}
+
+  bool Is(ExceptionType) const { return mVariant.template is<ErrorResult>(); }
+
+  template <IDBSpecialValue Special>
+  bool Is(SpecialConstant<Special>) const {
+    return mVariant.template is<SpecialConstant<Special>>();
+  }
+
+  ErrorResult& AsException() { return mVariant.template as<ErrorResult>(); }
+
+  template <typename... SpecialValueMappers>
+  ErrorResult ExtractErrorResult(SpecialValueMappers... aSpecialValueMappers) {
+#if defined(__clang__) || (defined(__GNUC__) && __GNUC__ >= 8)
+    return mVariant.match(
+        [](ErrorResult& aException) { return std::move(aException); },
+        [aSpecialValueMappers](const SpecialConstant<S>& aSpecialValue) {
+          return ErrorResult{aSpecialValueMappers(aSpecialValue)};
+        }...);
+#else
+    // gcc 7 doesn't accept the kind of parameter pack expansion above,
+    // probably due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47226
+    return mVariant.match([aSpecialValueMappers...](auto& aValue) {
+      if constexpr (std::is_same_v<ErrorResult&, decltype(aValue)>) {
+        return std::move(aValue);
+      } else {
+        return ErrorResult{aSpecialValueMappers(aValue)...};
+      }
+    });
+#endif
+  }
+
+  template <typename... SpecialValueMappers>
+  nsresult ExtractNSResult(SpecialValueMappers... aSpecialValueMappers) {
+    return mVariant.match(
+        [](ErrorResult& aException) { return aException.StealNSResult(); },
+        aSpecialValueMappers...);
+  }
+
+ protected:
+  using VariantType = Variant<ErrorResult, SpecialConstant<S>...>;
+
+  VariantType mVariant;
+};
+}  // namespace detail
+
+// Represents a return value of an IndexedDB algorithm. T is the type of the
+// regular return value, while S is a list of special values that can be
+// returned by the particular algorithm.
+template <typename T, IDBSpecialValue... S>
+using IDBResult = Result<T, detail::IDBError<S...>>;
+
+template <nsresult E>
+nsresult InvalidMapsTo(const indexedDB::detail::InvalidType&) {
+  return E;
+}
+
+inline detail::IDBError<> IDBException(nsresult aRv) {
+  return {SpecialValues::Exception, ErrorResult{aRv}};
+}
+
+template <IDBSpecialValue Special>
+detail::IDBError<Special> IDBError(detail::SpecialConstant<Special> aResult) {
+  return {aResult};
+}
+
+}  // namespace mozilla::dom::indexedDB
+
+#endif  // mozilla_dom_indexeddb_idbresult_h__