llvm/llvm/include/llvm/Support/FileSystem.h

//===- llvm/Support/FileSystem.h - File System OS Concept -------*- 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 declares the llvm::sys::fs namespace. It is designed after
// TR2/boost filesystem (v3), but modified to remove exception handling and the
// path class.
//
// All functions return an error_code and their actual work via the last out
// argument. The out argument is defined if and only if errc::success is
// returned. A function may return any error code in the generic or system
// category. However, they shall be equivalent to any error conditions listed
// in each functions respective documentation if the condition applies. [ note:
// this does not guarantee that error_code will be in the set of explicitly
// listed codes, but it does guarantee that if any of the explicitly listed
// errors occur, the correct error_code will be used ]. All functions may
// return errc::not_enough_memory if there is not enough memory to complete the
// operation.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_FILESYSTEM_H
#define LLVM_SUPPORT_FILESYSTEM_H

#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/Chrono.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/FileSystem/UniqueID.h"
#include "llvm/Support/MD5.h"
#include <cassert>
#include <cstdint>
#include <ctime>
#include <memory>
#include <string>
#include <system_error>
#include <vector>

#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif

namespace llvm {
namespace sys {
namespace fs {

#if defined(_WIN32)
// A Win32 HANDLE is a typedef of void*
using file_t = void *;
#else
file_t;
#endif

extern const file_t kInvalidFile;

/// An enumeration for the file system's view of the type.
enum class file_type { … };

/// space_info - Self explanatory.
struct space_info { … };

enum perms { … };

// Helper functions so that you can use & and | to manipulate perms bits:
inline perms operator|(perms l, perms r) { … }
inline perms operator&(perms l, perms r) { … }
inline perms &operator|=(perms &l, perms r) { … }
inline perms &operator&=(perms &l, perms r) { … }
inline perms operator~(perms x) { … }

/// Represents the result of a call to directory_iterator::status(). This is a
/// subset of the information returned by a regular sys::fs::status() call, and
/// represents the information provided by Windows FileFirstFile/FindNextFile.
class basic_file_status { … };

/// Represents the result of a call to sys::fs::status().
class file_status : public basic_file_status { … };

/// @}
/// @name Physical Operators
/// @{

/// Make \a path an absolute path.
///
/// Makes \a path absolute using the \a current_directory if it is not already.
/// An empty \a path will result in the \a current_directory.
///
/// /absolute/path   => /absolute/path
/// relative/../path => <current-directory>/relative/../path
///
/// @param path A path that is modified to be an absolute path.
void make_absolute(const Twine &current_directory, SmallVectorImpl<char> &path);

/// Make \a path an absolute path.
///
/// Makes \a path absolute using the current directory if it is not already. An
/// empty \a path will result in the current directory.
///
/// /absolute/path   => /absolute/path
/// relative/../path => <current-directory>/relative/../path
///
/// @param path A path that is modified to be an absolute path.
/// @returns errc::success if \a path has been made absolute, otherwise a
///          platform-specific error_code.
std::error_code make_absolute(SmallVectorImpl<char> &path);

/// Create all the non-existent directories in path.
///
/// @param path Directories to create.
/// @returns errc::success if is_directory(path), otherwise a platform
///          specific error_code. If IgnoreExisting is false, also returns
///          error if the directory already existed.
std::error_code create_directories(const Twine &path,
                                   bool IgnoreExisting = true,
                                   perms Perms = owner_all | group_all);

/// Create the directory in path.
///
/// @param path Directory to create.
/// @returns errc::success if is_directory(path), otherwise a platform
///          specific error_code. If IgnoreExisting is false, also returns
///          error if the directory already existed.
std::error_code create_directory(const Twine &path, bool IgnoreExisting = true,
                                 perms Perms = owner_all | group_all);

/// Create a link from \a from to \a to.
///
/// The link may be a soft or a hard link, depending on the platform. The caller
/// may not assume which one. Currently on windows it creates a hard link since
/// soft links require extra privileges. On unix, it creates a soft link since
/// hard links don't work on SMB file systems.
///
/// @param to The path to hard link to.
/// @param from The path to hard link from. This is created.
/// @returns errc::success if the link was created, otherwise a platform
/// specific error_code.
std::error_code create_link(const Twine &to, const Twine &from);

/// Create a hard link from \a from to \a to, or return an error.
///
/// @param to The path to hard link to.
/// @param from The path to hard link from. This is created.
/// @returns errc::success if the link was created, otherwise a platform
/// specific error_code.
std::error_code create_hard_link(const Twine &to, const Twine &from);

/// Collapse all . and .. patterns, resolve all symlinks, and optionally
///        expand ~ expressions to the user's home directory.
///
/// @param path The path to resolve.
/// @param output The location to store the resolved path.
/// @param expand_tilde If true, resolves ~ expressions to the user's home
///                     directory.
std::error_code real_path(const Twine &path, SmallVectorImpl<char> &output,
                          bool expand_tilde = false);

/// Expands ~ expressions to the user's home directory. On Unix ~user
/// directories are resolved as well.
///
/// @param path The path to resolve.
void expand_tilde(const Twine &path, SmallVectorImpl<char> &output);

/// Get the current path.
///
/// @param result Holds the current path on return.
/// @returns errc::success if the current path has been stored in result,
///          otherwise a platform-specific error_code.
std::error_code current_path(SmallVectorImpl<char> &result);

/// Set the current path.
///
/// @param path The path to set.
/// @returns errc::success if the current path was successfully set,
///          otherwise a platform-specific error_code.
std::error_code set_current_path(const Twine &path);

/// Remove path. Equivalent to POSIX remove().
///
/// @param path Input path.
/// @returns errc::success if path has been removed or didn't exist, otherwise a
///          platform-specific error code. If IgnoreNonExisting is false, also
///          returns error if the file didn't exist.
std::error_code remove(const Twine &path, bool IgnoreNonExisting = true);

/// Recursively delete a directory.
///
/// @param path Input path.
/// @returns errc::success if path has been removed or didn't exist, otherwise a
///          platform-specific error code.
std::error_code remove_directories(const Twine &path, bool IgnoreErrors = true);

/// Rename \a from to \a to.
///
/// Files are renamed as if by POSIX rename(), except that on Windows there may
/// be a short interval of time during which the destination file does not
/// exist.
///
/// @param from The path to rename from.
/// @param to The path to rename to. This is created.
std::error_code rename(const Twine &from, const Twine &to);

/// Copy the contents of \a From to \a To.
///
/// @param From The path to copy from.
/// @param To The path to copy to. This is created.
std::error_code copy_file(const Twine &From, const Twine &To);

/// Copy the contents of \a From to \a To.
///
/// @param From The path to copy from.
/// @param ToFD The open file descriptor of the destination file.
std::error_code copy_file(const Twine &From, int ToFD);

/// Resize path to size. File is resized as if by POSIX truncate().
///
/// @param FD Input file descriptor.
/// @param Size Size to resize to.
/// @returns errc::success if \a path has been resized to \a size, otherwise a
///          platform-specific error_code.
std::error_code resize_file(int FD, uint64_t Size);

/// Resize \p FD to \p Size before mapping \a mapped_file_region::readwrite. On
/// non-Windows, this calls \a resize_file(). On Windows, this is a no-op,
/// since the subsequent mapping (via \c CreateFileMapping) automatically
/// extends the file.
inline std::error_code resize_file_before_mapping_readwrite(int FD,
                                                            uint64_t Size) { … }

/// Compute an MD5 hash of a file's contents.
///
/// @param FD Input file descriptor.
/// @returns An MD5Result with the hash computed, if successful, otherwise a
///          std::error_code.
ErrorOr<MD5::MD5Result> md5_contents(int FD);

/// Version of compute_md5 that doesn't require an open file descriptor.
ErrorOr<MD5::MD5Result> md5_contents(const Twine &Path);

/// @}
/// @name Physical Observers
/// @{

/// Does file exist?
///
/// @param status A basic_file_status previously returned from stat.
/// @returns True if the file represented by status exists, false if it does
///          not.
bool exists(const basic_file_status &status);

enum class AccessMode { … };

/// Can the file be accessed?
///
/// @param Path Input path.
/// @returns errc::success if the path can be accessed, otherwise a
///          platform-specific error_code.
std::error_code access(const Twine &Path, AccessMode Mode);

/// Does file exist?
///
/// @param Path Input path.
/// @returns True if it exists, false otherwise.
inline bool exists(const Twine &Path) { … }

/// Can we execute this file?
///
/// @param Path Input path.
/// @returns True if we can execute it, false otherwise.
bool can_execute(const Twine &Path);

/// Can we write this file?
///
/// @param Path Input path.
/// @returns True if we can write to it, false otherwise.
inline bool can_write(const Twine &Path) { … }

/// Do file_status's represent the same thing?
///
/// @param A Input file_status.
/// @param B Input file_status.
///
/// assert(status_known(A) || status_known(B));
///
/// @returns True if A and B both represent the same file system entity, false
///          otherwise.
bool equivalent(file_status A, file_status B);

/// Do paths represent the same thing?
///
/// assert(status_known(A) || status_known(B));
///
/// @param A Input path A.
/// @param B Input path B.
/// @param result Set to true if stat(A) and stat(B) have the same device and
///               inode (or equivalent).
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code equivalent(const Twine &A, const Twine &B, bool &result);

/// Simpler version of equivalent for clients that don't need to
///        differentiate between an error and false.
inline bool equivalent(const Twine &A, const Twine &B) { … }

/// Is the file mounted on a local filesystem?
///
/// @param path Input path.
/// @param result Set to true if \a path is on fixed media such as a hard disk,
///               false if it is not.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform specific error_code.
std::error_code is_local(const Twine &path, bool &result);

/// Version of is_local accepting an open file descriptor.
std::error_code is_local(int FD, bool &result);

/// Simpler version of is_local for clients that don't need to
///        differentiate between an error and false.
inline bool is_local(const Twine &Path) { … }

/// Simpler version of is_local accepting an open file descriptor for
///        clients that don't need to differentiate between an error and false.
inline bool is_local(int FD) { … }

/// Does status represent a directory?
///
/// @param Path The path to get the type of.
/// @param Follow For symbolic links, indicates whether to return the file type
///               of the link itself, or of the target.
/// @returns A value from the file_type enumeration indicating the type of file.
file_type get_file_type(const Twine &Path, bool Follow = true);

/// Does status represent a directory?
///
/// @param status A basic_file_status previously returned from status.
/// @returns status.type() == file_type::directory_file.
bool is_directory(const basic_file_status &status);

/// Is path a directory?
///
/// @param path Input path.
/// @param result Set to true if \a path is a directory (after following
///               symlinks, false if it is not. Undefined otherwise.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code is_directory(const Twine &path, bool &result);

/// Simpler version of is_directory for clients that don't need to
///        differentiate between an error and false.
inline bool is_directory(const Twine &Path) { … }

/// Does status represent a regular file?
///
/// @param status A basic_file_status previously returned from status.
/// @returns status_known(status) && status.type() == file_type::regular_file.
bool is_regular_file(const basic_file_status &status);

/// Is path a regular file?
///
/// @param path Input path.
/// @param result Set to true if \a path is a regular file (after following
///               symlinks), false if it is not. Undefined otherwise.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code is_regular_file(const Twine &path, bool &result);

/// Simpler version of is_regular_file for clients that don't need to
///        differentiate between an error and false.
inline bool is_regular_file(const Twine &Path) { … }

/// Does status represent a symlink file?
///
/// @param status A basic_file_status previously returned from status.
/// @returns status_known(status) && status.type() == file_type::symlink_file.
bool is_symlink_file(const basic_file_status &status);

/// Is path a symlink file?
///
/// @param path Input path.
/// @param result Set to true if \a path is a symlink file, false if it is not.
///               Undefined otherwise.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code is_symlink_file(const Twine &path, bool &result);

/// Simpler version of is_symlink_file for clients that don't need to
///        differentiate between an error and false.
inline bool is_symlink_file(const Twine &Path) { … }

/// Does this status represent something that exists but is not a
///        directory or regular file?
///
/// @param status A basic_file_status previously returned from status.
/// @returns exists(s) && !is_regular_file(s) && !is_directory(s)
bool is_other(const basic_file_status &status);

/// Is path something that exists but is not a directory,
///        regular file, or symlink?
///
/// @param path Input path.
/// @param result Set to true if \a path exists, but is not a directory, regular
///               file, or a symlink, false if it does not. Undefined otherwise.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code is_other(const Twine &path, bool &result);

/// Get file status as if by POSIX stat().
///
/// @param path Input path.
/// @param result Set to the file status.
/// @param follow When true, follows symlinks.  Otherwise, the symlink itself is
///               statted.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code status(const Twine &path, file_status &result,
                       bool follow = true);

/// A version for when a file descriptor is already available.
std::error_code status(int FD, file_status &Result);

#ifdef _WIN32
/// A version for when a file descriptor is already available.
std::error_code status(file_t FD, file_status &Result);
#endif

/// Get file creation mode mask of the process.
///
/// @returns Mask reported by umask(2)
/// @note There is no umask on Windows. This function returns 0 always
///       on Windows. This function does not return an error_code because
///       umask(2) never fails. It is not thread safe.
unsigned getUmask();

/// Set file permissions.
///
/// @param Path File to set permissions on.
/// @param Permissions New file permissions.
/// @returns errc::success if the permissions were successfully set, otherwise
///          a platform-specific error_code.
/// @note On Windows, all permissions except *_write are ignored. Using any of
///       owner_write, group_write, or all_write will make the file writable.
///       Otherwise, the file will be marked as read-only.
std::error_code setPermissions(const Twine &Path, perms Permissions);

/// Vesion of setPermissions accepting a file descriptor.
/// TODO Delete the path based overload once we implement the FD based overload
/// on Windows.
std::error_code setPermissions(int FD, perms Permissions);

/// Get file permissions.
///
/// @param Path File to get permissions from.
/// @returns the permissions if they were successfully retrieved, otherwise a
///          platform-specific error_code.
/// @note On Windows, if the file does not have the FILE_ATTRIBUTE_READONLY
///       attribute, all_all will be returned. Otherwise, all_read | all_exe
///       will be returned.
ErrorOr<perms> getPermissions(const Twine &Path);

/// Get file size.
///
/// @param Path Input path.
/// @param Result Set to the size of the file in \a Path.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
inline std::error_code file_size(const Twine &Path, uint64_t &Result) { … }

/// Set the file modification and access time.
///
/// @returns errc::success if the file times were successfully set, otherwise a
///          platform-specific error_code or errc::function_not_supported on
///          platforms where the functionality isn't available.
std::error_code setLastAccessAndModificationTime(int FD, TimePoint<> AccessTime,
                                                 TimePoint<> ModificationTime);

/// Simpler version that sets both file modification and access time to the same
/// time.
inline std::error_code setLastAccessAndModificationTime(int FD,
                                                        TimePoint<> Time) { … }

/// Is status available?
///
/// @param s Input file status.
/// @returns True if status() != status_error.
bool status_known(const basic_file_status &s);

/// Is status available?
///
/// @param path Input path.
/// @param result Set to true if status() != status_error.
/// @returns errc::success if result has been successfully set, otherwise a
///          platform-specific error_code.
std::error_code status_known(const Twine &path, bool &result);

enum CreationDisposition : unsigned { … };

enum FileAccess : unsigned { … };

enum OpenFlags : unsigned { … };

/// Create a potentially unique file name but does not create it.
///
/// Generates a unique path suitable for a temporary file but does not
/// open or create the file. The name is based on \a Model with '%'
/// replaced by a random char in [0-9a-f]. If \a MakeAbsolute is true
/// then the system's temp directory is prepended first. If \a MakeAbsolute
/// is false the current directory will be used instead.
///
/// This function does not check if the file exists. If you want to be sure
/// that the file does not yet exist, you should use enough '%' characters
/// in your model to ensure this. Each '%' gives 4-bits of entropy so you can
/// use 32 of them to get 128 bits of entropy.
///
/// Example: clang-%%-%%-%%-%%-%%.s => clang-a0-b1-c2-d3-e4.s
///
/// @param Model Name to base unique path off of.
/// @param ResultPath Set to the file's path.
/// @param MakeAbsolute Whether to use the system temp directory.
void createUniquePath(const Twine &Model, SmallVectorImpl<char> &ResultPath,
                      bool MakeAbsolute);

/// Create a uniquely named file.
///
/// Generates a unique path suitable for a temporary file and then opens it as a
/// file. The name is based on \a Model with '%' replaced by a random char in
/// [0-9a-f]. If \a Model is not an absolute path, the temporary file will be
/// created in the current directory.
///
/// Example: clang-%%-%%-%%-%%-%%.s => clang-a0-b1-c2-d3-e4.s
///
/// This is an atomic operation. Either the file is created and opened, or the
/// file system is left untouched.
///
/// The intended use is for files that are to be kept, possibly after
/// renaming them. For example, when running 'clang -c foo.o', the file can
/// be first created as foo-abc123.o and then renamed.
///
/// @param Model Name to base unique path off of.
/// @param ResultFD Set to the opened file's file descriptor.
/// @param ResultPath Set to the opened file's absolute path.
/// @param Flags Set to the opened file's flags.
/// @param Mode Set to the opened file's permissions.
/// @returns errc::success if Result{FD,Path} have been successfully set,
///          otherwise a platform-specific error_code.
std::error_code createUniqueFile(const Twine &Model, int &ResultFD,
                                 SmallVectorImpl<char> &ResultPath,
                                 OpenFlags Flags = OF_None,
                                 unsigned Mode = all_read | all_write);

/// Simpler version for clients that don't want an open file. An empty
/// file will still be created.
std::error_code createUniqueFile(const Twine &Model,
                                 SmallVectorImpl<char> &ResultPath,
                                 unsigned Mode = all_read | all_write);

/// Represents a temporary file.
///
/// The temporary file must be eventually discarded or given a final name and
/// kept.
///
/// The destructor doesn't implicitly discard because there is no way to
/// properly handle errors in a destructor.
class TempFile { … };

/// Create a file in the system temporary directory.
///
/// The filename is of the form prefix-random_chars.suffix. Since the directory
/// is not know to the caller, Prefix and Suffix cannot have path separators.
/// The files are created with mode 0600.
///
/// This should be used for things like a temporary .s that is removed after
/// running the assembler.
std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
                                    int &ResultFD,
                                    SmallVectorImpl<char> &ResultPath,
                                    OpenFlags Flags = OF_None);

/// Simpler version for clients that don't want an open file. An empty
/// file will still be created.
std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
                                    SmallVectorImpl<char> &ResultPath,
                                    OpenFlags Flags = OF_None);

std::error_code createUniqueDirectory(const Twine &Prefix,
                                      SmallVectorImpl<char> &ResultPath);

/// Get a unique name, not currently exisiting in the filesystem. Subject
/// to race conditions, prefer to use createUniqueFile instead.
///
/// Similar to createUniqueFile, but instead of creating a file only
/// checks if it exists. This function is subject to race conditions, if you
/// want to use the returned name to actually create a file, use
/// createUniqueFile instead.
std::error_code getPotentiallyUniqueFileName(const Twine &Model,
                                             SmallVectorImpl<char> &ResultPath);

/// Get a unique temporary file name, not currently exisiting in the
/// filesystem. Subject to race conditions, prefer to use createTemporaryFile
/// instead.
///
/// Similar to createTemporaryFile, but instead of creating a file only
/// checks if it exists. This function is subject to race conditions, if you
/// want to use the returned name to actually create a file, use
/// createTemporaryFile instead.
std::error_code
getPotentiallyUniqueTempFileName(const Twine &Prefix, StringRef Suffix,
                                 SmallVectorImpl<char> &ResultPath);

inline OpenFlags operator|(OpenFlags A, OpenFlags B) { … }

inline OpenFlags &operator|=(OpenFlags &A, OpenFlags B) { … }

inline FileAccess operator|(FileAccess A, FileAccess B) { … }

inline FileAccess &operator|=(FileAccess &A, FileAccess B) { … }

/// @brief Opens a file with the specified creation disposition, access mode,
/// and flags and returns a file descriptor.
///
/// The caller is responsible for closing the file descriptor once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param ResultFD If the file could be opened successfully, its descriptor
///                 is stored in this location. Otherwise, this is set to -1.
/// @param Disp Value specifying the existing-file behavior.
/// @param Access Value specifying whether to open the file in read, write, or
///               read-write mode.
/// @param Flags Additional flags.
/// @param Mode The access permissions of the file, represented in octal.
/// @returns errc::success if \a Name has been opened, otherwise a
///          platform-specific error_code.
std::error_code openFile(const Twine &Name, int &ResultFD,
                         CreationDisposition Disp, FileAccess Access,
                         OpenFlags Flags, unsigned Mode = 0666);

/// @brief Opens a file with the specified creation disposition, access mode,
/// and flags and returns a platform-specific file object.
///
/// The caller is responsible for closing the file object once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param Disp Value specifying the existing-file behavior.
/// @param Access Value specifying whether to open the file in read, write, or
///               read-write mode.
/// @param Flags Additional flags.
/// @param Mode The access permissions of the file, represented in octal.
/// @returns errc::success if \a Name has been opened, otherwise a
///          platform-specific error_code.
Expected<file_t> openNativeFile(const Twine &Name, CreationDisposition Disp,
                                FileAccess Access, OpenFlags Flags,
                                unsigned Mode = 0666);

/// Converts from a Posix file descriptor number to a native file handle.
/// On Windows, this retreives the underlying handle. On non-Windows, this is a
/// no-op.
file_t convertFDToNativeFile(int FD);

#ifndef _WIN32
inline file_t convertFDToNativeFile(int FD) { … }
#endif

/// Return an open handle to standard in. On Unix, this is typically FD 0.
/// Returns kInvalidFile when the stream is closed.
file_t getStdinHandle();

/// Return an open handle to standard out. On Unix, this is typically FD 1.
/// Returns kInvalidFile when the stream is closed.
file_t getStdoutHandle();

/// Return an open handle to standard error. On Unix, this is typically FD 2.
/// Returns kInvalidFile when the stream is closed.
file_t getStderrHandle();

/// Reads \p Buf.size() bytes from \p FileHandle into \p Buf. Returns the number
/// of bytes actually read. On Unix, this is equivalent to `return ::read(FD,
/// Buf.data(), Buf.size())`, with error reporting. Returns 0 when reaching EOF.
///
/// @param FileHandle File to read from.
/// @param Buf Buffer to read into.
/// @returns The number of bytes read, or error.
Expected<size_t> readNativeFile(file_t FileHandle, MutableArrayRef<char> Buf);

/// Default chunk size for \a readNativeFileToEOF().
enum : size_t { … };

/// Reads from \p FileHandle until EOF, appending to \p Buffer in chunks of
/// size \p ChunkSize.
///
/// This calls \a readNativeFile() in a loop. On Error, previous chunks that
/// were read successfully are left in \p Buffer and returned.
///
/// Note: For reading the final chunk at EOF, \p Buffer's capacity needs extra
/// storage of \p ChunkSize.
///
/// \param FileHandle File to read from.
/// \param Buffer Where to put the file content.
/// \param ChunkSize Size of chunks.
/// \returns The error if EOF was not found.
Error readNativeFileToEOF(file_t FileHandle, SmallVectorImpl<char> &Buffer,
                          ssize_t ChunkSize = DefaultReadChunkSize);

/// Reads \p Buf.size() bytes from \p FileHandle at offset \p Offset into \p
/// Buf. If 'pread' is available, this will use that, otherwise it will use
/// 'lseek'. Returns the number of bytes actually read. Returns 0 when reaching
/// EOF.
///
/// @param FileHandle File to read from.
/// @param Buf Buffer to read into.
/// @param Offset Offset into the file at which the read should occur.
/// @returns The number of bytes read, or error.
Expected<size_t> readNativeFileSlice(file_t FileHandle,
                                     MutableArrayRef<char> Buf,
                                     uint64_t Offset);

/// @brief Opens the file with the given name in a write-only or read-write
/// mode, returning its open file descriptor. If the file does not exist, it
/// is created.
///
/// The caller is responsible for closing the file descriptor once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param ResultFD If the file could be opened successfully, its descriptor
///                 is stored in this location. Otherwise, this is set to -1.
/// @param Flags Additional flags used to determine whether the file should be
///              opened in, for example, read-write or in write-only mode.
/// @param Mode The access permissions of the file, represented in octal.
/// @returns errc::success if \a Name has been opened, otherwise a
///          platform-specific error_code.
inline std::error_code
openFileForWrite(const Twine &Name, int &ResultFD,
                 CreationDisposition Disp = CD_CreateAlways,
                 OpenFlags Flags = OF_None, unsigned Mode = 0666) { … }

/// @brief Opens the file with the given name in a write-only or read-write
/// mode, returning its open file descriptor. If the file does not exist, it
/// is created.
///
/// The caller is responsible for closing the freeing the file once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param Flags Additional flags used to determine whether the file should be
///              opened in, for example, read-write or in write-only mode.
/// @param Mode The access permissions of the file, represented in octal.
/// @returns a platform-specific file descriptor if \a Name has been opened,
///          otherwise an error object.
inline Expected<file_t> openNativeFileForWrite(const Twine &Name,
                                               CreationDisposition Disp,
                                               OpenFlags Flags,
                                               unsigned Mode = 0666) { … }

/// @brief Opens the file with the given name in a write-only or read-write
/// mode, returning its open file descriptor. If the file does not exist, it
/// is created.
///
/// The caller is responsible for closing the file descriptor once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param ResultFD If the file could be opened successfully, its descriptor
///                 is stored in this location. Otherwise, this is set to -1.
/// @param Flags Additional flags used to determine whether the file should be
///              opened in, for example, read-write or in write-only mode.
/// @param Mode The access permissions of the file, represented in octal.
/// @returns errc::success if \a Name has been opened, otherwise a
///          platform-specific error_code.
inline std::error_code openFileForReadWrite(const Twine &Name, int &ResultFD,
                                            CreationDisposition Disp,
                                            OpenFlags Flags,
                                            unsigned Mode = 0666) { … }

/// @brief Opens the file with the given name in a write-only or read-write
/// mode, returning its open file descriptor. If the file does not exist, it
/// is created.
///
/// The caller is responsible for closing the freeing the file once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param Flags Additional flags used to determine whether the file should be
///              opened in, for example, read-write or in write-only mode.
/// @param Mode The access permissions of the file, represented in octal.
/// @returns a platform-specific file descriptor if \a Name has been opened,
///          otherwise an error object.
inline Expected<file_t> openNativeFileForReadWrite(const Twine &Name,
                                                   CreationDisposition Disp,
                                                   OpenFlags Flags,
                                                   unsigned Mode = 0666) { … }

/// @brief Opens the file with the given name in a read-only mode, returning
/// its open file descriptor.
///
/// The caller is responsible for closing the file descriptor once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param ResultFD If the file could be opened successfully, its descriptor
///                 is stored in this location. Otherwise, this is set to -1.
/// @param RealPath If nonnull, extra work is done to determine the real path
///                 of the opened file, and that path is stored in this
///                 location.
/// @returns errc::success if \a Name has been opened, otherwise a
///          platform-specific error_code.
std::error_code openFileForRead(const Twine &Name, int &ResultFD,
                                OpenFlags Flags = OF_None,
                                SmallVectorImpl<char> *RealPath = nullptr);

/// @brief Opens the file with the given name in a read-only mode, returning
/// its open file descriptor.
///
/// The caller is responsible for closing the freeing the file once they are
/// finished with it.
///
/// @param Name The path of the file to open, relative or absolute.
/// @param RealPath If nonnull, extra work is done to determine the real path
///                 of the opened file, and that path is stored in this
///                 location.
/// @returns a platform-specific file descriptor if \a Name has been opened,
///          otherwise an error object.
Expected<file_t>
openNativeFileForRead(const Twine &Name, OpenFlags Flags = OF_None,
                      SmallVectorImpl<char> *RealPath = nullptr);

/// Try to locks the file during the specified time.
///
/// This function implements advisory locking on entire file. If it returns
/// <em>errc::success</em>, the file is locked by the calling process. Until the
/// process unlocks the file by calling \a unlockFile, all attempts to lock the
/// same file will fail/block. The process that locked the file may assume that
/// none of other processes read or write this file, provided that all processes
/// lock the file prior to accessing its content.
///
/// @param FD      The descriptor representing the file to lock.
/// @param Timeout Time in milliseconds that the process should wait before
///                reporting lock failure. Zero value means try to get lock only
///                once.
/// @returns errc::success if lock is successfully obtained,
/// errc::no_lock_available if the file cannot be locked, or platform-specific
/// error_code otherwise.
///
/// @note Care should be taken when using this function in a multithreaded
/// context, as it may not prevent other threads in the same process from
/// obtaining a lock on the same file, even if they are using a different file
/// descriptor.
std::error_code
tryLockFile(int FD,
            std::chrono::milliseconds Timeout = std::chrono::milliseconds(0));

/// Lock the file.
///
/// This function acts as @ref tryLockFile but it waits infinitely.
std::error_code lockFile(int FD);

/// Unlock the file.
///
/// @param FD The descriptor representing the file to unlock.
/// @returns errc::success if lock is successfully released or platform-specific
/// error_code otherwise.
std::error_code unlockFile(int FD);

/// @brief Close the file object.  This should be used instead of ::close for
/// portability. On error, the caller should assume the file is closed, as is
/// the case for Process::SafelyCloseFileDescriptor
///
/// @param F On input, this is the file to close.  On output, the file is
/// set to kInvalidFile.
///
/// @returns An error code if closing the file failed. Typically, an error here
/// means that the filesystem may have failed to perform some buffered writes.
std::error_code closeFile(file_t &F);

#ifdef LLVM_ON_UNIX
/// @brief Change ownership of a file.
///
/// @param Owner The owner of the file to change to.
/// @param Group The group of the file to change to.
/// @returns errc::success if successfully updated file ownership, otherwise an
///          error code is returned.
std::error_code changeFileOwnership(int FD, uint32_t Owner, uint32_t Group);
#endif

/// RAII class that facilitates file locking.
class FileLocker { … };

std::error_code getUniqueID(const Twine Path, UniqueID &Result);

/// Get disk space usage information.
///
/// Note: Users must be careful about "Time Of Check, Time Of Use" kind of bug.
/// Note: Windows reports results according to the quota allocated to the user.
///
/// @param Path Input path.
/// @returns a space_info structure filled with the capacity, free, and
/// available space on the device \a Path is on. A platform specific error_code
/// is returned on error.
ErrorOr<space_info> disk_space(const Twine &Path);

/// This class represents a memory mapped file. It is based on
/// boost::iostreams::mapped_file.
class mapped_file_region { … };

/// Return the path to the main executable, given the value of argv[0] from
/// program startup and the address of main itself. In extremis, this function
/// may fail and return an empty path.
std::string getMainExecutable(const char *argv0, void *MainExecAddr);

/// @}
/// @name Iterators
/// @{

/// directory_entry - A single entry in a directory.
class directory_entry { … };

namespace detail {

  struct DirIterState;

  std::error_code directory_iterator_construct(DirIterState &, StringRef, bool);
  std::error_code directory_iterator_increment(DirIterState &);
  std::error_code directory_iterator_destruct(DirIterState &);

  /// Keeps state for the directory_iterator.
  struct DirIterState { … };

} // end namespace detail

/// directory_iterator - Iterates through the entries in path. There is no
/// operator++ because we need an error_code. If it's really needed we can make
/// it call report_fatal_error on error.
class directory_iterator { … };

namespace detail {

  /// Keeps state for the recursive_directory_iterator.
  struct RecDirIterState { … };

} // end namespace detail

/// recursive_directory_iterator - Same as directory_iterator except for it
/// recurses down into child directories.
class recursive_directory_iterator { … };

/// @}

} // end namespace fs
} // end namespace sys
} // end namespace llvm

#endif // LLVM_SUPPORT_FILESYSTEM_H