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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_AUTOFILL_CORE_COMMON_LOGGING_LOG_MACROS_H_
#define COMPONENTS_AUTOFILL_CORE_COMMON_LOGGING_LOG_MACROS_H_
// Logging macro in the style of LOG(INFO) intended for
// chrome://autofill-internals.
//
// In `LOG_AF(logger) << expression`, the `expression` is evaluated only
// if the `logger` is active. The expression `logger` must be of type
// `LogManager` or `LogBuffer` or `LogManager*` or `LogBuffer`*.
//
// Support for other types of `logger` can be added by adding template
// specializations of `LoggerTraits`.
//
// This macro works as follows:
// LOG_AF(logger) << foo();
// expands to
// !active(logger) ? (void)0 : Voidify() & get_stream(logger) << foo();
// Due to the operator precedence, this is equivalent to:
// !active(logger) ? (void)0 : (Voidify() & (get_stream(logger) << foo()));
// If the logger is inactive, this is equivalent to the no-op
// (void)0;
// and otherwise it is equivalent to
// get_stream(logger) << foo();
#define LOG_AF(logger) \
!::autofill::internal::LoggerTraits<decltype(logger)>::active(logger) \
? (void)0 \
: ::autofill::internal::Voidify() & \
::autofill::internal::LoggerTraits<decltype(logger)>::get_stream( \
logger)
namespace autofill::internal {
// Traits for targets of LOG_AF(). There are currently specializations for
// `LogManager*` and `LogBuffer*`. The below is just a placeholder.
template <typename T>
struct LoggerTraits {
class Null {
public:
constexpr Null() = default;
template <typename U>
Null operator<<(const U&) {
return {};
}
};
// Returns true iff logging to should be enabled.
static bool active(const T& logger) {
static_assert(
false,
"Traits for this logger aren't visible. Are you missing an include of "
"log_manager.h and/or log_buffer.h?");
return false;
}
// Returns an object that implements the stream insertion operator
// operator<<().
static Null get_stream(const T& logger) {
static_assert(
false,
"Traits for this logger aren't visible. Are you missing an include of "
"log_manager.h and/or log_buffer.h?");
return {};
}
};
// This class is used to explicitly ignore values in the conditional
// logging macros. This avoids compiler warnings like "value computed
// is not used" and "statement has no effect".
class Voidify {
public:
constexpr Voidify() = default;
// This has to be an operator with a precedence lower than << but
// higher than ?:
template <typename U>
void operator&(const U&) {}
};
} // namespace autofill::internal
#endif // COMPONENTS_AUTOFILL_CORE_COMMON_LOGGING_LOG_MACROS_H_
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