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Diffstat (limited to 'mfbt/DbgMacro.h')
| -rw-r--r-- | mfbt/DbgMacro.h | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/mfbt/DbgMacro.h b/mfbt/DbgMacro.h new file mode 100644 index 0000000000..3247b993c0 --- /dev/null +++ b/mfbt/DbgMacro.h @@ -0,0 +1,206 @@ +/* -*- 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/. */ + +#ifndef mozilla_DbgMacro_h +#define mozilla_DbgMacro_h + +/* a MOZ_DBG macro that outputs a wrapped value to stderr then returns it */ + +#include "mozilla/MacroForEach.h" +#include "mozilla/Span.h" + +#include <stdio.h> +#include <sstream> + +template <typename T> +class nsTSubstring; + +#ifdef ANDROID +# include <android/log.h> +#endif + +namespace mozilla { + +namespace detail { + +// Predicate to check whether T can be inserted into an ostream. +template <typename T, typename = decltype(std::declval<std::ostream&>() + << std::declval<T>())> +std::true_type supports_os_test(const T&); +std::false_type supports_os_test(...); + +template <typename T> +using supports_os = decltype(supports_os_test(std::declval<T>())); + +} // namespace detail + +// Helper function to write a value to an ostream. +// +// This handles pointer values where the type being pointed to supports being +// inserted into an ostream, and we write out the value being pointed to in +// addition to the pointer value. +template <typename T> +auto DebugValue(std::ostream& aOut, T* aValue) + -> std::enable_if_t<mozilla::detail::supports_os<T>::value, std::ostream&> { + if (aValue) { + aOut << *aValue << " @ " << aValue; + } else { + aOut << "null"; + } + return aOut; +} + +// Helper function to write a value to an ostream. +// +// This handles all pointer types that cannot be dereferenced and inserted into +// an ostream. +template <typename T> +auto DebugValue(std::ostream& aOut, T* aValue) + -> std::enable_if_t<!mozilla::detail::supports_os<T>::value, + std::ostream&> { + return aOut << aValue; +} + +// Helper function to write a value to an ostream. +// +// This handles XPCOM string types. +template <typename T> +auto DebugValue(std::ostream& aOut, const T& aValue) + -> std::enable_if_t<std::is_base_of<nsTSubstring<char>, T>::value || + std::is_base_of<nsTSubstring<char16_t>, T>::value, + std::ostream&> { + return aOut << '"' << aValue << '"'; +} + +// Helper function to write a value to an ostream. +// +// This handles all other types. +template <typename T> +auto DebugValue(std::ostream& aOut, const T& aValue) + -> std::enable_if_t<!std::is_base_of<nsTSubstring<char>, T>::value && + !std::is_base_of<nsTSubstring<char16_t>, T>::value, + std::ostream&> { + return aOut << aValue; +} + +namespace detail { + +// Helper function template for MOZ_DBG. +template <typename T> +auto&& MozDbg(const char* aFile, int aLine, const char* aExpression, + T&& aValue) { + std::ostringstream s; + s << "[MozDbg] [" << aFile << ':' << aLine << "] " << aExpression << " = "; + mozilla::DebugValue(s, std::forward<T>(aValue)); + s << '\n'; +#ifdef ANDROID + __android_log_print(ANDROID_LOG_INFO, "Gecko", "%s", s.str().c_str()); +#else + fputs(s.str().c_str(), stderr); +#endif + return std::forward<T>(aValue); +} + +} // namespace detail + +} // namespace mozilla + +template <class ElementType, size_t Extent> +std::ostream& operator<<(std::ostream& aOut, + const mozilla::Span<ElementType, Extent>& aSpan) { + aOut << '['; + if (!aSpan.IsEmpty()) { + aOut << aSpan[0]; + for (size_t i = 1; i < aSpan.Length(); ++i) { + aOut << ", " << aSpan[i]; + } + } + return aOut << ']'; +} + +// Don't define this for char[], since operator<<(ostream&, char*) is already +// defined. +template <typename T, size_t N, + typename = std::enable_if_t<!std::is_same<T, char>::value>> +std::ostream& operator<<(std::ostream& aOut, const T (&aArray)[N]) { + return aOut << mozilla::Span(aArray); +} + +// MOZ_DBG is a macro like the Rust dbg!() macro -- it will print out the +// expression passed to it to stderr and then return the value. It is not +// available in MOZILLA_OFFICIAL builds, so you shouldn't land any uses of it in +// the tree. +// +// It should work for any type T that has an operator<<(std::ostream&, const T&) +// defined for it. +// +// Note 1: Using MOZ_DBG may cause copies to be made of temporary values: +// +// struct A { +// A(int); +// A(const A&); +// +// int x; +// }; +// +// void f(A); +// +// f(A{1}); // may (and, in C++17, will) elide the creation of a temporary +// // for A{1} and instead initialize the function argument +// // directly using the A(int) constructor +// +// f(MOZ_DBG(A{1})); // will create and return a temporary for A{1}, which +// // then will be passed to the A(const A&) copy +// // constructor to initialize f's argument +// +// Note 2: MOZ_DBG cannot be used to wrap a prvalue that is being used to +// initialize an object if its type has no move constructor: +// +// struct B { +// B() = default; +// B(B&&) = delete; +// }; +// +// B b1 = B(); // fine, initializes b1 directly +// +// B b2 = MOZ_DBG(B()); // compile error: MOZ_DBG needs to materialize a +// // temporary for B() so it can be passed to +// // operator<<, but that temporary is returned from +// // MOZ_DBG as an rvalue reference and so wants to +// // invoke B's move constructor to initialize b2 +#ifndef MOZILLA_OFFICIAL +# define MOZ_DBG(...) \ + mozilla::detail::MozDbg(__FILE__, __LINE__, #__VA_ARGS__, __VA_ARGS__) +#endif + +// Helper macro for MOZ_DEFINE_DBG. +#define MOZ_DBG_FIELD(name_) << #name_ << " = " << aValue.name_ + +// Macro to define an operator<<(ostream&) for a struct or class that displays +// the type name and the values of the specified member variables. Must be +// called inside the struct or class. +// +// For example: +// +// struct Point { +// float x; +// float y; +// +// MOZ_DEFINE_DBG(Point, x, y) +// }; +// +// generates an operator<< that outputs strings like +// "Point { x = 1.0, y = 2.0 }". +#define MOZ_DEFINE_DBG(type_, ...) \ + friend std::ostream& operator<<(std::ostream& aOut, const type_& aValue) { \ + return aOut << #type_ \ + << (MOZ_ARG_COUNT(__VA_ARGS__) == 0 ? "" : " { ") \ + MOZ_FOR_EACH_SEPARATED(MOZ_DBG_FIELD, (<< ", "), (), \ + (__VA_ARGS__)) \ + << (MOZ_ARG_COUNT(__VA_ARGS__) == 0 ? "" : " }"); \ + } + +#endif // mozilla_DbgMacro_h |