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/* -*- 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
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