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Diffstat (limited to 'mfbt/ResultExtensions.h')
| -rw-r--r-- | mfbt/ResultExtensions.h | 371 |
1 files changed, 371 insertions, 0 deletions
diff --git a/mfbt/ResultExtensions.h b/mfbt/ResultExtensions.h new file mode 100644 index 0000000000..97f197d800 --- /dev/null +++ b/mfbt/ResultExtensions.h @@ -0,0 +1,371 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * 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/. */ + +/* Extensions to the Result type to enable simpler handling of XPCOM/NSPR + * results. */ + +#ifndef mozilla_ResultExtensions_h +#define mozilla_ResultExtensions_h + +#include "mozilla/Assertions.h" +#include "nscore.h" +#include "prtypes.h" +#include "mozilla/dom/quota/RemoveParen.h" + +namespace mozilla { + +struct ErrorPropagationTag; + +// Allow nsresult errors to automatically convert to nsresult values, so MOZ_TRY +// can be used in XPCOM methods with Result<T, nserror> results. +template <> +class [[nodiscard]] GenericErrorResult<nsresult> { + nsresult mErrorValue; + + template <typename V, typename E2> + friend class Result; + + public: + explicit GenericErrorResult(nsresult aErrorValue) : mErrorValue(aErrorValue) { + MOZ_ASSERT(NS_FAILED(aErrorValue)); + } + + GenericErrorResult(nsresult aErrorValue, const ErrorPropagationTag&) + : GenericErrorResult(aErrorValue) {} + + operator nsresult() const { return mErrorValue; } +}; + +// Allow MOZ_TRY to handle `PRStatus` values. +template <typename E = nsresult> +inline Result<Ok, E> ToResult(PRStatus aValue); + +} // namespace mozilla + +#include "mozilla/Result.h" + +namespace mozilla { + +template <typename ResultType> +struct ResultTypeTraits; + +template <> +struct ResultTypeTraits<nsresult> { + static nsresult From(nsresult aValue) { return aValue; } +}; + +template <typename E> +inline Result<Ok, E> ToResult(nsresult aValue) { + if (NS_FAILED(aValue)) { + return Err(ResultTypeTraits<E>::From(aValue)); + } + return Ok(); +} + +template <typename E> +inline Result<Ok, E> ToResult(PRStatus aValue) { + if (aValue == PR_SUCCESS) { + return Ok(); + } + return Err(ResultTypeTraits<E>::From(NS_ERROR_FAILURE)); +} + +namespace detail { +template <typename R> +auto ResultRefAsParam(R& aResult) { + return &aResult; +} + +template <typename R, typename E, typename RArgMapper, typename Func, + typename... Args> +Result<R, E> ToResultInvokeInternal(const Func& aFunc, + const RArgMapper& aRArgMapper, + Args&&... aArgs) { + // XXX Thereotically, if R is a pointer to a non-refcounted type, this might + // be a non-owning pointer, but unless we find a case where this actually is + // relevant, it's safe to forbid any raw pointer result. + static_assert( + !std::is_pointer_v<R>, + "Raw pointer results are not supported, please specify a smart pointer " + "result type explicitly, so that getter_AddRefs is used"); + + R res; + nsresult rv = aFunc(std::forward<Args>(aArgs)..., aRArgMapper(res)); + if (NS_FAILED(rv)) { + return Err(ResultTypeTraits<E>::From(rv)); + } + return res; +} + +template <typename T> +struct outparam_as_pointer; + +template <typename T> +struct outparam_as_pointer<T*> { + using type = T*; +}; + +template <typename T> +struct outparam_as_reference; + +template <typename T> +struct outparam_as_reference<T*> { + using type = T&; +}; + +template <typename R, typename E, template <typename> typename RArg, + typename Func, typename... Args> +using to_result_retval_t = + decltype(std::declval<Func&>()( + std::declval<Args&&>()..., + std::declval<typename RArg<decltype(ResultRefAsParam( + std::declval<R&>()))>::type>()), + Result<R, E>(Err(ResultTypeTraits<E>::From(NS_ERROR_FAILURE)))); + +// There are two ToResultInvokeSelector overloads, which cover the cases of a) a +// pointer-typed output parameter, and b) a reference-typed output parameter, +// using to_result_retval_t in connection with outparam_as_pointer and +// outparam_as_reference type traits. These type traits may be specialized for +// types other than raw pointers to allow calling functions with argument types +// that implicitly convert/bind to a raw pointer/reference. The overload that is +// used is selected by expression SFINAE: the decltype expression in +// to_result_retval_t is only valid in either case. +template <typename R, typename E, typename Func, typename... Args> +auto ToResultInvokeSelector(const Func& aFunc, Args&&... aArgs) + -> to_result_retval_t<R, E, outparam_as_pointer, Func, Args...> { + return ToResultInvokeInternal<R, E>( + aFunc, [](R& res) -> decltype(auto) { return ResultRefAsParam(res); }, + std::forward<Args>(aArgs)...); +} + +template <typename R, typename E, typename Func, typename... Args> +auto ToResultInvokeSelector(const Func& aFunc, Args&&... aArgs) + -> to_result_retval_t<R, E, outparam_as_reference, Func, Args...> { + return ToResultInvokeInternal<R, E>( + aFunc, [](R& res) -> decltype(auto) { return *ResultRefAsParam(res); }, + std::forward<Args>(aArgs)...); +} + +} // namespace detail + +/** + * Adapts a function with a nsresult error type and an R* output parameter as + * the last parameter to a function returning a mozilla::Result<R, nsresult> + * object. + * + * This can also be used with member functions together with std::men_fn, e.g. + * + * nsCOMPtr<nsIFile> file = ...; + * auto existsOrErr = ToResultInvoke<bool>(std::mem_fn(&nsIFile::Exists), + * *file); + * + * but it is more convenient to use the member function version, which has the + * additional benefit of enabling the deduction of the success result type: + * + * nsCOMPtr<nsIFile> file = ...; + * auto existsOrErr = ToResultInvokeMember(*file, &nsIFile::Exists); + */ +template <typename R, typename E = nsresult, typename Func, typename... Args> +Result<R, E> ToResultInvoke(const Func& aFunc, Args&&... aArgs) { + return detail::ToResultInvokeSelector<R, E, Func, Args&&...>( + aFunc, std::forward<Args>(aArgs)...); +} + +namespace detail { +template <typename T> +struct tag { + using type = T; +}; + +template <typename... Ts> +struct select_last { + using type = typename decltype((tag<Ts>{}, ...))::type; +}; + +template <typename... Ts> +using select_last_t = typename select_last<Ts...>::type; + +template <> +struct select_last<> { + using type = void; +}; + +template <typename E, typename RArg, typename T, typename Func, + typename... Args> +auto ToResultInvokeMemberInternal(T& aObj, const Func& aFunc, Args&&... aArgs) { + if constexpr (std::is_pointer_v<RArg> || + (std::is_lvalue_reference_v<RArg> && + !std::is_const_v<std::remove_reference_t<RArg>>)) { + auto lambda = [&](RArg res) { + return (aObj.*aFunc)(std::forward<Args>(aArgs)..., res); + }; + return detail::ToResultInvokeSelector< + std::remove_reference_t<std::remove_pointer_t<RArg>>, E, + decltype(lambda)>(lambda); + } else { + // No output parameter present, return a Result<Ok, E> + return mozilla::ToResult<E>((aObj.*aFunc)(std::forward<Args>(aArgs)...)); + } +} + +// For use in MOZ_TO_RESULT_INVOKE_MEMBER/MOZ_TO_RESULT_INVOKE_MEMBER_TYPED. +template <typename T> +auto DerefHelper(const T&) -> T&; + +template <typename T> +auto DerefHelper(T*) -> T&; + +template <template <class> class SmartPtr, typename T, + typename = decltype(*std::declval<const SmartPtr<T>>())> +auto DerefHelper(const SmartPtr<T>&) -> T&; + +template <typename T> +using DerefedType = + std::remove_reference_t<decltype(DerefHelper(std::declval<const T&>()))>; +} // namespace detail + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>> +auto ToResultInvokeMember(T& aObj, nsresult (U::*aFunc)(XArgs...), + Args&&... aArgs) { + return detail::ToResultInvokeMemberInternal<E, + detail::select_last_t<XArgs...>>( + aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>> +auto ToResultInvokeMember(const T& aObj, nsresult (U::*aFunc)(XArgs...) const, + Args&&... aArgs) { + return detail::ToResultInvokeMemberInternal<E, + detail::select_last_t<XArgs...>>( + aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args> +auto ToResultInvokeMember(T* const aObj, nsresult (U::*aFunc)(XArgs...), + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args> +auto ToResultInvokeMember(const T* const aObj, + nsresult (U::*aFunc)(XArgs...) const, + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, template <class> class SmartPtr, typename T, + typename U, typename... XArgs, typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>, + typename = decltype(*std::declval<const SmartPtr<T>>())> +auto ToResultInvokeMember(const SmartPtr<T>& aObj, + nsresult (U::*aFunc)(XArgs...), Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, template <class> class SmartPtr, typename T, + typename U, typename... XArgs, typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>, + typename = decltype(*std::declval<const SmartPtr<T>>())> +auto ToResultInvokeMember(const SmartPtr<const T>& aObj, + nsresult (U::*aFunc)(XArgs...) const, + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +#if defined(XP_WIN) && !defined(_WIN64) +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>> +auto ToResultInvokeMember(T& aObj, nsresult (__stdcall U::*aFunc)(XArgs...), + Args&&... aArgs) { + return detail::ToResultInvokeMemberInternal<E, + detail::select_last_t<XArgs...>>( + aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>> +auto ToResultInvokeMember(const T& aObj, + nsresult (__stdcall U::*aFunc)(XArgs...) const, + Args&&... aArgs) { + return detail::ToResultInvokeMemberInternal<E, + detail::select_last_t<XArgs...>>( + aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args> +auto ToResultInvokeMember(T* const aObj, + nsresult (__stdcall U::*aFunc)(XArgs...), + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, typename T, typename U, typename... XArgs, + typename... Args> +auto ToResultInvokeMember(const T* const aObj, + nsresult (__stdcall U::*aFunc)(XArgs...) const, + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, template <class> class SmartPtr, typename T, + typename U, typename... XArgs, typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>, + typename = decltype(*std::declval<const SmartPtr<T>>())> +auto ToResultInvokeMember(const SmartPtr<T>& aObj, + nsresult (__stdcall U::*aFunc)(XArgs...), + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} + +template <typename E = nsresult, template <class> class SmartPtr, typename T, + typename U, typename... XArgs, typename... Args, + typename = std::enable_if_t<std::is_base_of_v<U, T>>, + typename = decltype(*std::declval<const SmartPtr<T>>())> +auto ToResultInvokeMember(const SmartPtr<const T>& aObj, + nsresult (__stdcall U::*aFunc)(XArgs...) const, + Args&&... aArgs) { + return ToResultInvokeMember<E>(*aObj, aFunc, std::forward<Args>(aArgs)...); +} +#endif + +// Macro version of ToResultInvokeMember for member functions. The macro has +// the advantage of not requiring spelling out the member function's declarator +// type name, at the expense of having a non-standard syntax. It can be used +// like this: +// +// nsCOMPtr<nsIFile> file; +// auto existsOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(file, Exists); +#define MOZ_TO_RESULT_INVOKE_MEMBER(obj, methodname, ...) \ + ::mozilla::ToResultInvokeMember( \ + (obj), &::mozilla::detail::DerefedType<decltype(obj)>::methodname, \ + ##__VA_ARGS__) + +// Macro version of ToResultInvokeMember for member functions, where the result +// type does not match the output parameter type. The macro has the advantage +// of not requiring spelling out the member function's declarator type name, at +// the expense of having a non-standard syntax. It can be used like this: +// +// nsCOMPtr<nsIFile> file; +// auto existsOrErr = +// MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(nsCOMPtr<nsIFile>, file, Clone); +#define MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(resultType, obj, methodname, ...) \ + ::mozilla::ToResultInvoke<MOZ_REMOVE_PAREN(resultType)>( \ + ::std::mem_fn( \ + &::mozilla::detail::DerefedType<decltype(obj)>::methodname), \ + (obj), ##__VA_ARGS__) + +} // namespace mozilla + +#endif // mozilla_ResultExtensions_h |