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//===--- raw_ostream.h - Raw output stream ----------------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

//  This file defines the raw_ostream class.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_RAW_OSTREAM_H

#define LLVM_SUPPORT_RAW_OSTREAM_H

#include "llvm/ADT/SmallVector.h"

#include "llvm/ADT/StringRef.h"

#include "llvm/Support/DataTypes.h"

#include <cassert>

#include <cstddef>

#include <cstdint>

#include <cstring>

#include <optional>

#include <string>

#include <string_view>

#include <system_error>

#include <type_traits>

namespace llvm {

class Duration;

class formatv_object_base;

class format_object_base;

class FormattedString;

class FormattedNumber;

class FormattedBytes;

template <class T> class [[nodiscard]] Expected;

namespace sys {

namespace fs {

enum FileAccess : unsigned;

enum OpenFlags : unsigned;

enum CreationDisposition : unsigned;

class FileLocker;

} // end namespace fs

} // end namespace sys

/// This class implements an extremely fast bulk output stream that can *only*

/// output to a stream.  It does not support seeking, reopening, rewinding, line

/// buffered disciplines etc. It is a simple buffer that outputs

/// a chunk at a time.

class raw_ostream {

public:

  // Class kinds to support LLVM-style RTTI.

  enum class OStreamKind {

    OK_OStream,

    OK_FDStream,

  };

private:

  OStreamKind Kind;

  /// The buffer is handled in such a way that the buffer is

  /// uninitialized, unbuffered, or out of space when OutBufCur >=

  /// OutBufEnd. Thus a single comparison suffices to determine if we

  /// need to take the slow path to write a single character.

  ///

  /// The buffer is in one of three states:

  ///  1. Unbuffered (BufferMode == Unbuffered)

  ///  1. Uninitialized (BufferMode != Unbuffered && OutBufStart == 0).

  ///  2. Buffered (BufferMode != Unbuffered && OutBufStart != 0 &&

  ///               OutBufEnd - OutBufStart >= 1).

  ///

  /// If buffered, then the raw_ostream owns the buffer if (BufferMode ==

  /// InternalBuffer); otherwise the buffer has been set via SetBuffer and is

  /// managed by the subclass.

  ///

  /// If a subclass installs an external buffer using SetBuffer then it can wait

  /// for a \see write_impl() call to handle the data which has been put into

  /// this buffer.

  char *OutBufStart, *OutBufEnd, *OutBufCur;

  bool ColorEnabled = false;

  /// Optional stream this stream is tied to. If this stream is written to, the

  /// tied-to stream will be flushed first.

  raw_ostream *TiedStream = nullptr;

  enum class BufferKind {

    Unbuffered = 0,

    InternalBuffer,

    ExternalBuffer

  } BufferMode;

public:

  // color order matches ANSI escape sequence, don't change

  enum class Colors {

    BLACK = 0,

    RED,

    GREEN,

    YELLOW,

    BLUE,

    MAGENTA,

    CYAN,

    WHITE,

    SAVEDCOLOR,

    RESET,

  };

  static constexpr Colors BLACK = Colors::BLACK;

  static constexpr Colors RED = Colors::RED;

  static constexpr Colors GREEN = Colors::GREEN;

  static constexpr Colors YELLOW = Colors::YELLOW;

  static constexpr Colors BLUE = Colors::BLUE;

  static constexpr Colors MAGENTA = Colors::MAGENTA;

  static constexpr Colors CYAN = Colors::CYAN;

  static constexpr Colors WHITE = Colors::WHITE;

  static constexpr Colors SAVEDCOLOR = Colors::SAVEDCOLOR;

  static constexpr Colors RESET = Colors::RESET;

  explicit raw_ostream(bool unbuffered = false,

                       OStreamKind K = OStreamKind::OK_OStream)

      : Kind(K), BufferMode(unbuffered ? BufferKind::Unbuffered

                                       : BufferKind::InternalBuffer) {

    // Start out ready to flush.

    OutBufStart = OutBufEnd = OutBufCur = nullptr;

  }

  raw_ostream(const raw_ostream &) = delete;

  void operator=(const raw_ostream &) = delete;

  virtual ~raw_ostream();

  /// tell - Return the current offset with the file.

  uint64_t tell() const { return current_pos() + GetNumBytesInBuffer(); }

  OStreamKind get_kind() const { return Kind; }

  //===--------------------------------------------------------------------===//

  // Configuration Interface

  //===--------------------------------------------------------------------===//

  /// If possible, pre-allocate \p ExtraSize bytes for stream data.

  /// i.e. it extends internal buffers to keep additional ExtraSize bytes.

  /// So that the stream could keep at least tell() + ExtraSize bytes

  /// without re-allocations. reserveExtraSpace() does not change

  /// the size/data of the stream.

  virtual void reserveExtraSpace(uint64_t ExtraSize) {}

  /// Set the stream to be buffered, with an automatically determined buffer

  /// size.

  void SetBuffered();

  /// Set the stream to be buffered, using the specified buffer size.

  void SetBufferSize(size_t Size) {

    flush();

    SetBufferAndMode(new char[Size], Size, BufferKind::InternalBuffer);

  }

  size_t GetBufferSize() const {

    // If we're supposed to be buffered but haven't actually gotten around

    // to allocating the buffer yet, return the value that would be used.

    if (BufferMode != BufferKind::Unbuffered && OutBufStart == nullptr)

      return preferred_buffer_size();

    // Otherwise just return the size of the allocated buffer.

    return OutBufEnd - OutBufStart;

  }

  /// Set the stream to be unbuffered. When unbuffered, the stream will flush

  /// after every write. This routine will also flush the buffer immediately

  /// when the stream is being set to unbuffered.

  void SetUnbuffered() {

    flush();

    SetBufferAndMode(nullptr, 0, BufferKind::Unbuffered);

  }

  size_t GetNumBytesInBuffer() const {

    return OutBufCur - OutBufStart;

  }

  //===--------------------------------------------------------------------===//

  // Data Output Interface

  //===--------------------------------------------------------------------===//

  void flush() {

    if (OutBufCur != OutBufStart)

      flush_nonempty();

  }

  raw_ostream &operator<<(char C) {

    if (OutBufCur >= OutBufEnd)

      return write(C);

    *OutBufCur++ = C;

    return *this;

  }

  raw_ostream &operator<<(unsigned char C) {

    if (OutBufCur >= OutBufEnd)

      return write(C);

    *OutBufCur++ = C;

    return *this;

  }

  raw_ostream &operator<<(signed char C) {

    if (OutBufCur >= OutBufEnd)

      return write(C);

    *OutBufCur++ = C;

    return *this;

  }

  raw_ostream &operator<<(StringRef Str) {

    // Inline fast path, particularly for strings with a known length.

    size_t Size = Str.size();

    // Make sure we can use the fast path.

    if (Size > (size_t)(OutBufEnd - OutBufCur))

      return write(Str.data(), Size);

    if (Size) {

      memcpy(OutBufCur, Str.data(), Size);

      OutBufCur += Size;

    }

    return *this;

  }

#if defined(__cpp_char8_t)

  // When using `char8_t *` integers or pointers are written to the ostream

  // instead of UTF-8 code as one might expect. This might lead to unexpected

  // behavior, especially as `u8""` literals are of type `char8_t*` instead of

  // type `char_t*` from C++20 onwards. Thus we disallow using them with

  // raw_ostreams.

  // If you have u8"" literals to stream, you can rewrite them as ordinary

  // literals with escape sequences

  // e.g.  replace `u8"\u00a0"` by `"\xc2\xa0"`

  // or use `reinterpret_cast`:

  // e.g. replace `u8"\u00a0"` by `reinterpret_cast<const char *>(u8"\u00a0")`

  raw_ostream &operator<<(const char8_t *Str) = delete;

#endif

  raw_ostream &operator<<(const char *Str) {

    // Inline fast path, particularly for constant strings where a sufficiently

    // smart compiler will simplify strlen.

    return this->operator<<(StringRef(Str));

  }

  raw_ostream &operator<<(const std::string &Str) {

    // Avoid the fast path, it would only increase code size for a marginal win.

    return write(Str.data(), Str.length());

  }

  raw_ostream &operator<<(const std::string_view &Str) {

    return write(Str.data(), Str.length());

  }

  raw_ostream &operator<<(const SmallVectorImpl<char> &Str) {

    return write(Str.data(), Str.size());

  }

  raw_ostream &operator<<(unsigned long N);

  raw_ostream &operator<<(long N);

  raw_ostream &operator<<(unsigned long long N);

  raw_ostream &operator<<(long long N);

  raw_ostream &operator<<(const void *P);

  raw_ostream &operator<<(unsigned int N) {

    return this->operator<<(static_cast<unsigned long>(N));

  }

  raw_ostream &operator<<(int N) {

    return this->operator<<(static_cast<long>(N));

  }

  raw_ostream &operator<<(double N);

  /// Output \p N in hexadecimal, without any prefix or padding.

  raw_ostream &write_hex(unsigned long long N);

  // Change the foreground color of text.

  raw_ostream &operator<<(Colors C);

  /// Output a formatted UUID with dash separators.

  using uuid_t = uint8_t[16];

  raw_ostream &write_uuid(const uuid_t UUID);

  /// Output \p Str, turning '\\', '\t', '\n', '"', and anything that doesn't

  /// satisfy llvm::isPrint into an escape sequence.

  raw_ostream &write_escaped(StringRef Str, bool UseHexEscapes = false);

  raw_ostream &write(unsigned char C);

  raw_ostream &write(const char *Ptr, size_t Size);

  // Formatted output, see the format() function in Support/Format.h.

  raw_ostream &operator<<(const format_object_base &Fmt);

  // Formatted output, see the leftJustify() function in Support/Format.h.

  raw_ostream &operator<<(const FormattedString &);

  // Formatted output, see the formatHex() function in Support/Format.h.

  raw_ostream &operator<<(const FormattedNumber &);

  // Formatted output, see the formatv() function in Support/FormatVariadic.h.

  raw_ostream &operator<<(const formatv_object_base &);

  // Formatted output, see the format_bytes() function in Support/Format.h.

  raw_ostream &operator<<(const FormattedBytes &);

  /// indent - Insert 'NumSpaces' spaces.

  raw_ostream &indent(unsigned NumSpaces);

  /// write_zeros - Insert 'NumZeros' nulls.

  raw_ostream &write_zeros(unsigned NumZeros);

  /// Changes the foreground color of text that will be output from this point

  /// forward.

  /// @param Color ANSI color to use, the special SAVEDCOLOR can be used to

  /// change only the bold attribute, and keep colors untouched

  /// @param Bold bold/brighter text, default false

  /// @param BG if true change the background, default: change foreground

  /// @returns itself so it can be used within << invocations

  virtual raw_ostream &changeColor(enum Colors Color, bool Bold = false,

                                   bool BG = false);

  /// Resets the colors to terminal defaults. Call this when you are done

  /// outputting colored text, or before program exit.

  virtual raw_ostream &resetColor();

  /// Reverses the foreground and background colors.

  virtual raw_ostream &reverseColor();

  /// This function determines if this stream is connected to a "tty" or

  /// "console" window. That is, the output would be displayed to the user

  /// rather than being put on a pipe or stored in a file.

  virtual bool is_displayed() const { return false; }

  /// This function determines if this stream is displayed and supports colors.

  /// The result is unaffected by calls to enable_color().

  virtual bool has_colors() const { return is_displayed(); }

  // Enable or disable colors. Once enable_colors(false) is called,

  // changeColor() has no effect until enable_colors(true) is called.

  virtual void enable_colors(bool enable) { ColorEnabled = enable; }

  bool colors_enabled() const { return ColorEnabled; }

  /// Tie this stream to the specified stream. Replaces any existing tied-to

  /// stream. Specifying a nullptr unties the stream.

  void tie(raw_ostream *TieTo) { TiedStream = TieTo; }

  //===--------------------------------------------------------------------===//

  // Subclass Interface

  //===--------------------------------------------------------------------===//

private:

  /// The is the piece of the class that is implemented by subclasses.  This

  /// writes the \p Size bytes starting at

  /// \p Ptr to the underlying stream.

  ///

  /// This function is guaranteed to only be called at a point at which it is

  /// safe for the subclass to install a new buffer via SetBuffer.

  ///

  /// \param Ptr The start of the data to be written. For buffered streams this

  /// is guaranteed to be the start of the buffer.

  ///

  /// \param Size The number of bytes to be written.

  ///

  /// \invariant { Size > 0 }

  virtual void write_impl(const char *Ptr, size_t Size) = 0;

  /// Return the current position within the stream, not counting the bytes

  /// currently in the buffer.

  virtual uint64_t current_pos() const = 0;

protected:

  /// Use the provided buffer as the raw_ostream buffer. This is intended for

  /// use only by subclasses which can arrange for the output to go directly

  /// into the desired output buffer, instead of being copied on each flush.

  void SetBuffer(char *BufferStart, size_t Size) {

    SetBufferAndMode(BufferStart, Size, BufferKind::ExternalBuffer);

  }

  /// Return an efficient buffer size for the underlying output mechanism.

  virtual size_t preferred_buffer_size() const;

  /// Return the beginning of the current stream buffer, or 0 if the stream is

  /// unbuffered.

  const char *getBufferStart() const { return OutBufStart; }

  //===--------------------------------------------------------------------===//

  // Private Interface

  //===--------------------------------------------------------------------===//

private:

  /// Install the given buffer and mode.

  void SetBufferAndMode(char *BufferStart, size_t Size, BufferKind Mode);

  /// Flush the current buffer, which is known to be non-empty. This outputs the

  /// currently buffered data and resets the buffer to empty.

  void flush_nonempty();

  /// Copy data into the buffer. Size must not be greater than the number of

  /// unused bytes in the buffer.

  void copy_to_buffer(const char *Ptr, size_t Size);

  /// Compute whether colors should be used and do the necessary work such as

  /// flushing. The result is affected by calls to enable_color().

  bool prepare_colors();

  /// Flush the tied-to stream (if present) and then write the required data.

  void flush_tied_then_write(const char *Ptr, size_t Size);

  virtual void anchor();

};

/// Call the appropriate insertion operator, given an rvalue reference to a

/// raw_ostream object and return a stream of the same type as the argument.

template <typename OStream, typename T>

std::enable_if_t<!std::is_reference<OStream>::value &&

                     std::is_base_of<raw_ostream, OStream>::value,

                 OStream &&>

operator<<(OStream &&OS, const T &Value) {

  OS << Value;

  return std::move(OS);

}

/// An abstract base class for streams implementations that also support a

/// pwrite operation. This is useful for code that can mostly stream out data,

/// but needs to patch in a header that needs to know the output size.

class raw_pwrite_stream : public raw_ostream {

  virtual void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) = 0;

  void anchor() override;

public:

  explicit raw_pwrite_stream(bool Unbuffered = false,

                             OStreamKind K = OStreamKind::OK_OStream)

      : raw_ostream(Unbuffered, K) {}

  void pwrite(const char *Ptr, size_t Size, uint64_t Offset) {

#ifndef NDEBUG

    uint64_t Pos = tell();

    // /dev/null always reports a pos of 0, so we cannot perform this check

    // in that case.

    if (Pos)

      assert(Size + Offset <= Pos && "We don't support extending the stream");

#endif

    pwrite_impl(Ptr, Size, Offset);

  }

};

//===----------------------------------------------------------------------===//

// File Output Streams

//===----------------------------------------------------------------------===//

/// A raw_ostream that writes to a file descriptor.

///

class raw_fd_ostream : public raw_pwrite_stream {

  int FD;

  bool ShouldClose;

  bool SupportsSeeking = false;

  bool IsRegularFile = false;

  mutable std::optional<bool> HasColors;

#ifdef _WIN32

  /// True if this fd refers to a Windows console device. Mintty and other

  /// terminal emulators are TTYs, but they are not consoles.

  bool IsWindowsConsole = false;

#endif

  std::error_code EC;

  uint64_t pos = 0;

  /// See raw_ostream::write_impl.

  void write_impl(const char *Ptr, size_t Size) override;

  void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) override;

  /// Return the current position within the stream, not counting the bytes

  /// currently in the buffer.

  uint64_t current_pos() const override { return pos; }

  /// Determine an efficient buffer size.

  size_t preferred_buffer_size() const override;

  void anchor() override;

protected:

  /// Set the flag indicating that an output error has been encountered.

  void error_detected(std::error_code EC) { this->EC = EC; }

  /// Return the file descriptor.

  int get_fd() const { return FD; }

  // Update the file position by increasing \p Delta.

  void inc_pos(uint64_t Delta) { pos += Delta; }

public:

  /// Open the specified file for writing. If an error occurs, information

  /// about the error is put into EC, and the stream should be immediately

  /// destroyed;

  /// \p Flags allows optional flags to control how the file will be opened.

  ///

  /// As a special case, if Filename is "-", then the stream will use

  /// STDOUT_FILENO instead of opening a file. This will not close the stdout

  /// descriptor.

  raw_fd_ostream(StringRef Filename, std::error_code &EC);

  raw_fd_ostream(StringRef Filename, std::error_code &EC,

                 sys::fs::CreationDisposition Disp);

  raw_fd_ostream(StringRef Filename, std::error_code &EC,

                 sys::fs::FileAccess Access);

  raw_fd_ostream(StringRef Filename, std::error_code &EC,

                 sys::fs::OpenFlags Flags);

  raw_fd_ostream(StringRef Filename, std::error_code &EC,

                 sys::fs::CreationDisposition Disp, sys::fs::FileAccess Access,

                 sys::fs::OpenFlags Flags);

  /// FD is the file descriptor that this writes to.  If ShouldClose is true,

  /// this closes the file when the stream is destroyed. If FD is for stdout or

  /// stderr, it will not be closed.

  raw_fd_ostream(int fd, bool shouldClose, bool unbuffered = false,

                 OStreamKind K = OStreamKind::OK_OStream);

  ~raw_fd_ostream() override;

  /// Manually flush the stream and close the file. Note that this does not call

  /// fsync.

  void close();

  bool supportsSeeking() const { return SupportsSeeking; }

  bool isRegularFile() const { return IsRegularFile; }

  /// Flushes the stream and repositions the underlying file descriptor position

  /// to the offset specified from the beginning of the file.

  uint64_t seek(uint64_t off);

  bool is_displayed() const override;

  bool has_colors() const override;

  std::error_code error() const { return EC; }

  /// Return the value of the flag in this raw_fd_ostream indicating whether an

  /// output error has been encountered.

  /// This doesn't implicitly flush any pending output.  Also, it doesn't

  /// guarantee to detect all errors unless the stream has been closed.

  bool has_error() const { return bool(EC); }

  /// Set the flag read by has_error() to false. If the error flag is set at the

  /// time when this raw_ostream's destructor is called, report_fatal_error is

  /// called to report the error. Use clear_error() after handling the error to

  /// avoid this behavior.

  ///

  ///   "Errors should never pass silently.

  ///    Unless explicitly silenced."

  ///      - from The Zen of Python, by Tim Peters

  ///

  void clear_error() { EC = std::error_code(); }

  /// Locks the underlying file.

  ///

  /// @returns RAII object that releases the lock upon leaving the scope, if the

  ///          locking was successful. Otherwise returns corresponding

  ///          error code.

  ///

  /// The function blocks the current thread until the lock become available or

  /// error occurs.

  ///

  /// Possible use of this function may be as follows:

  ///

  ///   @code{.cpp}

  ///   if (auto L = stream.lock()) {

  ///     // ... do action that require file to be locked.

  ///   } else {

  ///     handleAllErrors(std::move(L.takeError()), [&](ErrorInfoBase &EIB) {

  ///       // ... handle lock error.

  ///     });

  ///   }

  ///   @endcode

  [[nodiscard]] Expected<sys::fs::FileLocker> lock();

  /// Tries to lock the underlying file within the specified period.

  ///

  /// @returns RAII object that releases the lock upon leaving the scope, if the

  ///          locking was successful. Otherwise returns corresponding

  ///          error code.

  ///

  /// It is used as @ref lock.

  [[nodiscard]] Expected<sys::fs::FileLocker>

  tryLockFor(Duration const &Timeout);

};

/// This returns a reference to a raw_fd_ostream for standard output. Use it

/// like: outs() << "foo" << "bar";

raw_fd_ostream &outs();

/// This returns a reference to a raw_ostream for standard error.

/// Use it like: errs() << "foo" << "bar";

/// By default, the stream is tied to stdout to ensure stdout is flushed before

/// stderr is written, to ensure the error messages are written in their

/// expected place.

raw_fd_ostream &errs();

/// This returns a reference to a raw_ostream which simply discards output.

raw_ostream &nulls();

//===----------------------------------------------------------------------===//

// File Streams

//===----------------------------------------------------------------------===//

/// A raw_ostream of a file for reading/writing/seeking.

///

class raw_fd_stream : public raw_fd_ostream {

public:

  /// Open the specified file for reading/writing/seeking. If an error occurs,

  /// information about the error is put into EC, and the stream should be

  /// immediately destroyed.

  raw_fd_stream(StringRef Filename, std::error_code &EC);

  /// This reads the \p Size bytes into a buffer pointed by \p Ptr.

  ///

  /// \param Ptr The start of the buffer to hold data to be read.

  ///

  /// \param Size The number of bytes to be read.

  ///

  /// On success, the number of bytes read is returned, and the file position is

  /// advanced by this number. On error, -1 is returned, use error() to get the

  /// error code.

  ssize_t read(char *Ptr, size_t Size);

  /// Check if \p OS is a pointer of type raw_fd_stream*.

  static bool classof(const raw_ostream *OS);

};

//===----------------------------------------------------------------------===//

// Output Stream Adaptors

//===----------------------------------------------------------------------===//

/// A raw_ostream that writes to an std::string.  This is a simple adaptor

/// class. This class does not encounter output errors.

/// raw_string_ostream operates without a buffer, delegating all memory

/// management to the std::string. Thus the std::string is always up-to-date,

/// may be used directly and there is no need to call flush().

class raw_string_ostream : public raw_ostream {

  std::string &OS;

  /// See raw_ostream::write_impl.

  void write_impl(const char *Ptr, size_t Size) override;

  /// Return the current position within the stream, not counting the bytes

  /// currently in the buffer.

  uint64_t current_pos() const override { return OS.size(); }

public:

  explicit raw_string_ostream(std::string &O) : OS(O) {

    SetUnbuffered();

  }

  /// Returns the string's reference. In most cases it is better to simply use

  /// the underlying std::string directly.

  /// TODO: Consider removing this API.

  std::string &str() { return OS; }

  void reserveExtraSpace(uint64_t ExtraSize) override {

    OS.reserve(tell() + ExtraSize);

  }

};

/// A raw_ostream that writes to an SmallVector or SmallString.  This is a

/// simple adaptor class. This class does not encounter output errors.

/// raw_svector_ostream operates without a buffer, delegating all memory

/// management to the SmallString. Thus the SmallString is always up-to-date,

/// may be used directly and there is no need to call flush().

class raw_svector_ostream : public raw_pwrite_stream {

  SmallVectorImpl<char> &OS;

  /// See raw_ostream::write_impl.

  void write_impl(const char *Ptr, size_t Size) override;

  void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) override;

  /// Return the current position within the stream.

  uint64_t current_pos() const override;

public:

  /// Construct a new raw_svector_ostream.

  ///

  /// \param O The vector to write to; this should generally have at least 128

  /// bytes free to avoid any extraneous memory overhead.

  explicit raw_svector_ostream(SmallVectorImpl<char> &O) : OS(O) {

    SetUnbuffered();

  }

  ~raw_svector_ostream() override = default;

  void flush() = delete;

  /// Return a StringRef for the vector contents.

  StringRef str() const { return StringRef(OS.data(), OS.size()); }

  void reserveExtraSpace(uint64_t ExtraSize) override {

    OS.reserve(tell() + ExtraSize);

  }

};

/// A raw_ostream that discards all output.

class raw_null_ostream : public raw_pwrite_stream {

  /// See raw_ostream::write_impl.

  void write_impl(const char *Ptr, size_t size) override;

  void pwrite_impl(const char *Ptr, size_t Size, uint64_t Offset) override;

  /// Return the current position within the stream, not counting the bytes

  /// currently in the buffer.

  uint64_t current_pos() const override;

public:

  explicit raw_null_ostream() = default;

  ~raw_null_ostream() override;

};

class buffer_ostream : public raw_svector_ostream {

  raw_ostream &OS;

  SmallVector<char, 0> Buffer;

  void anchor() override;

public:

  buffer_ostream(raw_ostream &OS) : raw_svector_ostream(Buffer), OS(OS) {}

  ~buffer_ostream() override { OS << str(); }

};

class buffer_unique_ostream : public raw_svector_ostream {

  std::unique_ptr<raw_ostream> OS;

  SmallVector<char, 0> Buffer;

  void anchor() override;

public:

  buffer_unique_ostream(std::unique_ptr<raw_ostream> OS)

      : raw_svector_ostream(Buffer), OS(std::move(OS)) {

    // Turn off buffering on OS, which we now own, to avoid allocating a buffer

    // when the destructor writes only to be immediately flushed again.

    this->OS->SetUnbuffered();

  }

  ~buffer_unique_ostream() override { *OS << str(); }

};

class Error;

/// This helper creates an output stream and then passes it to \p Write.

/// The stream created is based on the specified \p OutputFileName:

/// llvm::outs for "-", raw_null_ostream for "/dev/null", and raw_fd_ostream

/// for other names. For raw_fd_ostream instances, the stream writes to

/// a temporary file. The final output file is atomically replaced with the

/// temporary file after the \p Write function is finished.

Error writeToOutput(StringRef OutputFileName,

                    std::function<Error(raw_ostream &)> Write);

raw_ostream &operator<<(raw_ostream &OS, std::nullopt_t);

template <typename T, typename = decltype(std::declval<raw_ostream &>()

                                          << std::declval<const T &>())>

raw_ostream &operator<<(raw_ostream &OS, const std::optional<T> &O) {

  if (O)

    OS << *O;

  else

    OS << std::nullopt;

  return OS;

}

} // end namespace llvm

#endif // LLVM_SUPPORT_RAW_OSTREAM_H