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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,
     OK_SVecStream,
   };
 
 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;
 
   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,
     BRIGHT_BLACK,
     BRIGHT_RED,
     BRIGHT_GREEN,
     BRIGHT_YELLOW,
     BRIGHT_BLUE,
     BRIGHT_MAGENTA,
     BRIGHT_CYAN,
     BRIGHT_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 BRIGHT_BLACK = Colors::BRIGHT_BLACK;
   static constexpr Colors BRIGHT_RED = Colors::BRIGHT_RED;
   static constexpr Colors BRIGHT_GREEN = Colors::BRIGHT_GREEN;
   static constexpr Colors BRIGHT_YELLOW = Colors::BRIGHT_YELLOW;
   static constexpr Colors BRIGHT_BLUE = Colors::BRIGHT_BLUE;
   static constexpr Colors BRIGHT_MAGENTA = Colors::BRIGHT_MAGENTA;
   static constexpr Colors BRIGHT_CYAN = Colors::BRIGHT_CYAN;
   static constexpr Colors BRIGHT_WHITE = Colors::BRIGHT_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) { (void)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; }
 
   //===--------------------------------------------------------------------===//
   // 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();
 
   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_v<OStream> &&
                      std::is_base_of_v<raw_ostream, OStream>,
                  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;
 
   /// 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;
 
 #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;
 
   /// Tie this stream to the specified stream. Replaces any existing tied-to
   /// stream. Specifying a nullptr unties the stream. This is intended for to
   /// tie errs() to outs(), so that outs() is flushed whenever something is
   /// written to errs(), preventing weird and hard-to-test output when stderr
   /// is redirected to stdout.
   void tie(raw_ostream *TieTo) { TiedStream = TieTo; }
 
   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);
 
   raw_fd_stream(int fd, bool shouldClose);
 
   /// 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)
       : raw_pwrite_stream(false, raw_ostream::OStreamKind::OK_SVecStream),
         OS(O) {
     // FIXME: here and in a few other places, set directly to unbuffered in the
     // ctor.
     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()); }
   SmallVectorImpl<char> &buffer() { return OS; }
 
   void reserveExtraSpace(uint64_t ExtraSize) override {
     OS.reserve(tell() + ExtraSize);
   }
 
   static bool classof(const raw_ostream *OS);
 };
 
 /// 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(); }
 };
 
 // Helper struct to add indentation to raw_ostream. Instead of
 // OS.indent(6) << "more stuff";
 // you can use
 // OS << indent(6) << "more stuff";
 // which has better ergonomics (and clang-formats better as well).
 //
 // If indentation is always in increments of a fixed value, you can use Scale
 // to set that value once. So indent(1, 2) will add 2 spaces and
 // indent(1,2) + 1 will add 4 spaces.
 struct indent {
   // Indentation is represented as `NumIndents` steps of size `Scale` each.
   unsigned NumIndents;
   unsigned Scale;
 
   explicit indent(unsigned NumIndents, unsigned Scale = 1)
       : NumIndents(NumIndents), Scale(Scale) {}
 
   // These arithmeric operators preserve scale.
   void operator+=(unsigned N) { NumIndents += N; }
   void operator-=(unsigned N) {
     assert(NumIndents >= N && "Indentation underflow");
     NumIndents -= N;
   }
   indent operator+(unsigned N) const { return indent(NumIndents + N, Scale); }
   indent operator-(unsigned N) const {
     assert(NumIndents >= N && "Indentation undeflow");
     return indent(NumIndents - N, Scale);
   }
   indent &operator++() { // Prefix ++.
     ++NumIndents;
     return *this;
   }
   indent operator++(int) { // Postfix ++.
     indent Old = *this;
     ++NumIndents;
     return Old;
   }
   indent &operator--() { // Prefix --.
     assert(NumIndents >= 1);
     --NumIndents;
     return *this;
   }
   indent operator--(int) { // Postfix --.
     indent Old = *this;
     assert(NumIndents >= 1);
     --NumIndents;
     return Old;
   }
   indent &operator=(unsigned N) {
     NumIndents = N;
     return *this;
   }
 };
 
 inline raw_ostream &operator<<(raw_ostream &OS, const indent &Indent) {
   return OS.indent(Indent.NumIndents * Indent.Scale);
 }
 
 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

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