base/check.h

// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_CHECK_H_
#define BASE_CHECK_H_

#include <iosfwd>

#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/dcheck_is_on.h"
#include "base/immediate_crash.h"
#include "base/location.h"

// This header defines the CHECK, DCHECK, and DPCHECK macros.
//
// CHECK dies with a fatal error if its condition is not true. It is not
// controlled by NDEBUG, so the check will be executed regardless of compilation
// mode.
//
// DCHECK, the "debug mode" check, is enabled depending on NDEBUG and
// DCHECK_ALWAYS_ON, and its severity depends on DCHECK_IS_CONFIGURABLE.
//
// (D)PCHECK is like (D)CHECK, but includes the system error code (c.f.
// perror(3)).
//
// Additional information can be streamed to these macros and will be included
// in the log output if the condition doesn't hold (you may need to include
// <ostream>):
//
//   CHECK(condition) << "Additional info.";
//
// The condition is evaluated exactly once. Even in build modes where e.g.
// DCHECK is disabled, the condition and any stream arguments are still
// referenced to avoid warnings about unused variables and functions.
//
// For the (D)CHECK_EQ, etc. macros, see base/check_op.h. However, that header
// is *significantly* larger than check.h, so try to avoid including it in
// header files.

namespace logging {

// Class used to explicitly ignore an ostream, and optionally a boolean value.
class VoidifyStream {
 public:
  VoidifyStream() = default;
  explicit VoidifyStream(bool) {}

  // This operator has lower precedence than << but higher than ?:
  void operator&(std::ostream&) {}
};

// Macro which uses but does not evaluate expr and any stream parameters.
#define EAT_CHECK_STREAM_PARAMS(expr) \
  true ? (void)0                      \
       : ::logging::VoidifyStream(expr) & (*::logging::g_swallow_stream)
BASE_EXPORT extern std::ostream* g_swallow_stream;

class LogMessage;

// Class used for raising a check error upon destruction.
class BASE_EXPORT CheckError {
 public:
  static CheckError Check(
      const char* condition,
      const base::Location& location = base::Location::Current());
  // Takes ownership over (free()s after using) `log_message_str`, for use with
  // CHECK_op macros.
  static CheckError CheckOp(
      char* log_message_str,
      const base::Location& location = base::Location::Current());

  static CheckError DCheck(
      const char* condition,
      const base::Location& location = base::Location::Current());
  // Takes ownership over (free()s after using) `log_message_str`, for use with
  // DCHECK_op macros.
  static CheckError DCheckOp(
      char* log_message_str,
      const base::Location& location = base::Location::Current());

  static CheckError DumpWillBeCheck(
      const char* condition,
      const base::Location& location = base::Location::Current());
  // Takes ownership over (free()s after using) `log_message_str`, for use with
  // DUMP_WILL_BE_CHECK_op macros.
  static CheckError DumpWillBeCheckOp(
      char* log_message_str,
      const base::Location& location = base::Location::Current());

  static CheckError PCheck(
      const char* condition,
      const base::Location& location = base::Location::Current());
  static CheckError PCheck(
      const base::Location& location = base::Location::Current());

  static CheckError DPCheck(
      const char* condition,
      const base::Location& location = base::Location::Current());

  static CheckError DumpWillBeNotReachedNoreturn(
      const base::Location& location = base::Location::Current());

  static CheckError NotImplemented(
      const char* function,
      const base::Location& location = base::Location::Current());

  // Stream for adding optional details to the error message.
  std::ostream& stream();

  // Try really hard to get the call site and callee as separate stack frames in
  // crash reports.
  NOMERGE NOINLINE NOT_TAIL_CALLED ~CheckError();

  CheckError(const CheckError&) = delete;
  CheckError& operator=(const CheckError&) = delete;

  template <typename T>
  std::ostream& operator<<(T&& streamed_type) {
    return stream() << streamed_type;
  }

 protected:
  // Takes ownership of `log_message`.
  explicit CheckError(LogMessage* log_message) : log_message_(log_message) {}

  LogMessage* const log_message_;
};

class BASE_EXPORT NotReachedError : public CheckError {
 public:
  static NotReachedError NotReached(
      const base::Location& location = base::Location::Current());

  // Used to trigger a NOTREACHED() without providing file or line while also
  // discarding log-stream arguments. See base/notreached.h.
  NOMERGE NOINLINE NOT_TAIL_CALLED static void TriggerNotReached();

  // TODO(crbug.com/851128): Mark [[noreturn]] once this is CHECK-fatal on all
  // builds.
  NOMERGE NOINLINE NOT_TAIL_CALLED ~NotReachedError();

 private:
  using CheckError::CheckError;
};

// TODO(crbug.com/851128): This should take the name of the above class once all
// callers of NOTREACHED() have migrated to the CHECK-fatal version.
class BASE_EXPORT NotReachedNoreturnError : public CheckError {
 public:
  explicit NotReachedNoreturnError(
      const base::Location& location = base::Location::Current());

  [[noreturn]] NOMERGE NOINLINE NOT_TAIL_CALLED ~NotReachedNoreturnError();
};

// A helper macro for checks that log to streams that makes it easier for the
// compiler to identify and warn about dead code, e.g.:
//
//   return 2;
//   NOTREACHED();
//
// The 'switch' is used to prevent the 'else' from being ambiguous when the
// macro is used in an 'if' clause such as:
// if (a == 1)
//   CHECK(Foo());
//
// TODO(crbug.com/1380930): Remove the const bool when the blink-gc plugin has
// been updated to accept `if (LIKELY(!field_))` as well as `if (!field_)`.
#define LOGGING_CHECK_FUNCTION_IMPL(check_stream, condition)              \
  switch (0)                                                              \
  case 0:                                                                 \
  default:                                                                \
    /* Hint to the optimizer that `condition` is unlikely to be false. */ \
    /* The optimizer can use this as a hint to place the failure path */  \
    /* out-of-line, e.g. at the tail of the function. */                  \
    if (const bool probably_true = static_cast<bool>(condition);          \
        LIKELY(ANALYZER_ASSUME_TRUE(probably_true)))                      \
      ;                                                                   \
    else                                                                  \
      (check_stream)

#if defined(OFFICIAL_BUILD) && !defined(NDEBUG)
#error "Debug builds are not expected to be optimized as official builds."
#endif  // defined(OFFICIAL_BUILD) && !defined(NDEBUG)

#if defined(OFFICIAL_BUILD) && !DCHECK_IS_ON()
// Note that this uses IMMEDIATE_CRASH_ALWAYS_INLINE to force-inline in debug
// mode as well. See LoggingTest.CheckCausesDistinctBreakpoints.
[[noreturn]] IMMEDIATE_CRASH_ALWAYS_INLINE void CheckFailure() {
  base::ImmediateCrash();
}

// Discard log strings to reduce code bloat.
//
// This is not calling BreakDebugger since this is called frequently, and
// calling an out-of-line function instead of a noreturn inline macro prevents
// compiler optimizations. Unlike the other check macros, this one does not use
// LOGGING_CHECK_FUNCTION_IMPL(), since it is incompatible with
// EAT_CHECK_STREAM_PARAMETERS().
#define CHECK(condition) \
  UNLIKELY(!(condition)) ? logging::CheckFailure() : EAT_CHECK_STREAM_PARAMS()

#define CHECK_WILL_STREAM() false

// Strip the conditional string from official builds.
#define PCHECK(condition) \
  LOGGING_CHECK_FUNCTION_IMPL(::logging::CheckError::PCheck(), condition)

#else

#define CHECK_WILL_STREAM() true

#define CHECK(condition)                                                \
  LOGGING_CHECK_FUNCTION_IMPL(::logging::CheckError::Check(#condition), \
                              condition)

#define PCHECK(condition)                                                \
  LOGGING_CHECK_FUNCTION_IMPL(::logging::CheckError::PCheck(#condition), \
                              condition)

#endif

#if DCHECK_IS_ON()

#define DCHECK(condition)                                                \
  LOGGING_CHECK_FUNCTION_IMPL(::logging::CheckError::DCheck(#condition), \
                              condition)
#define DPCHECK(condition)                                                \
  LOGGING_CHECK_FUNCTION_IMPL(::logging::CheckError::DPCheck(#condition), \
                              condition)

#else

#define DCHECK(condition) EAT_CHECK_STREAM_PARAMS(!(condition))
#define DPCHECK(condition) EAT_CHECK_STREAM_PARAMS(!(condition))

#endif  // DCHECK_IS_ON()

// The DUMP_WILL_BE_CHECK() macro provides a convenient way to non-fatally dump
// in official builds if a condition is false. This is used to more cautiously
// roll out a new CHECK() (or upgrade a DCHECK) where the caller isn't entirely
// sure that something holds true in practice (but asserts that it should). This
// is especially useful for platforms that have a low pre-stable population and
// code areas that are rarely exercised.
//
// On DCHECK builds this macro matches DCHECK behavior.
//
// This macro isn't optimized (preserves filename, line number and log messages
// in official builds), as they are expected to be in product temporarily. When
// using this macro, leave a TODO(crbug.com/nnnn) entry referring to a bug
// related to its rollout. Then put a NextAction on the bug to come back and
// clean this up (replace with a CHECK). A DUMP_WILL_BE_CHECK() that's been left
// untouched for a long time without bug updates suggests that issues that
// would've prevented enabling this CHECK have either not been discovered or
// have been resolved.
//
// Using this macro is preferred over direct base::debug::DumpWithoutCrashing()
// invocations as it communicates intent to eventually end up as a CHECK. It
// also preserves the log message so setting crash keys to get additional debug
// info isn't required as often.
#define DUMP_WILL_BE_CHECK(condition) \
  LOGGING_CHECK_FUNCTION_IMPL(        \
      ::logging::CheckError::DumpWillBeCheck(#condition), condition)

// Async signal safe checking mechanism.
[[noreturn]] BASE_EXPORT void RawCheckFailure(const char* message);
#define RAW_CHECK(condition)                                        \
  do {                                                              \
    if (UNLIKELY(!(condition))) {                                   \
      ::logging::RawCheckFailure("Check failed: " #condition "\n"); \
    }                                                               \
  } while (0)

}  // namespace logging

#endif  // BASE_CHECK_H_