Proposed Resolution of C++17 National Body Comments for Filesystems(R1)

US 60; 27.10.8.4.9 [path.decompose] ¶6: path("/foo/").filename()==path(".") is surprising
Status: Accept with modifications

US 55; 27.10.8.4.5 [path.modifiers] ¶11: replace_extension()'s use of path as parameter is inappropriate
Status: Accept with modifications

The SG believes path is the appropriate parameter type, but that the standard needs to clarify class path usage.

Change 27.10.8 [class.path] ¶1:

An object of class path represents a path (27.10.4.17) and contains a pathname (27.10.4.18). Such an object is concerned only with the lexical and syntactic aspects of a path. The path does not necessarily exist in external storage, and the pathname is not necessarily valid for the current operating system or for a particular file system.

[Note: Class path is used to support the differences between the string types used by different operating systems to represent pathnames, and to perform conversions between encodings when necessary. — end note]

US 56; 27.10.8.4.5 [path.modifiers] ¶11.2: Remove replace_extension()'s conditional addition of period
Status: Reject

Nico presented this to the Library Evolution Working group in Issaquah, including a number of examples (See Nico's Filesystem: Filename Issues slides on the Issaquah LEWG wiki.) There was no consensus for change; the vote was 3/3/3/7/2. See the Issaquah LEWG notes.

US 57; 27.10.8.4.8 [path.compare] ¶2: On Windows, absolute paths will sort in among relative paths
Status: Reject

Insufficient motivation for change.

US 58; 27.10.8.4.9 [path.decompose] ¶5: parent_path() behavior for root paths is useless
Status: Accept with modifications

Change [path.decompose]:

path parent_path() const;

-?- Let parentEnd be an instance of path::iterator, initialized as follows:

• if has_relative_path(), from --end()
• otherwise, from end()

-5- Returns: (empty() || begin() == --end()) ? path() : pp, where pp is a path constructed as if by starting with an empty path and successively applying operator/= for each element in the range [begin(), --end()parentEnd).

US 59; 27.10.8.4.9 [path.decompose] ¶6: filename() returning path for single path components is bizarre
Status: Reject

path is filesystem's vocabulary type for both full paths and for path components, in the same sense that std::string might be used as the vocabulary type for both sentences and the words in the sentences. See US 55 for further discussion.

US 61; 27.10.8.4.9 [path.decompose] ¶8: Leading dots in filename() should not begin an extension
Status: Accept with modifications

Nico Josuttis presented this to the Library Evolution Working group in Issaquah, including a number of examples (See Nico's Filesystem: Filename Issues slides on the Issaquah LEWG wiki.) Support was unanimous. See the Issaquah LEWG notes.

Nico presented the following cases; the only change from the TS is for the ".profile" case:

path p	p.stem()	p.extension()
"/foo/bar.txt"	"bar"	".txt"
".profile"	"" ".profile"	".profile" ""
".profile.old"	".profile"	".old"
"..abc"	"..abc"	""
"...abc"	"...abc"	""
"abc..def"	"abc."	".def"
"abc...def"	"abc.."	".def"
"abc."	"abc"	"."
"abc.."	"abc."	"."
"abc.d."	"abc.d"	"."
".."	".."	""
"."	"."	""

Change 27.10.8.4.9 [path.decompose] ¶ 8:

path stem() const;

Returns: if filename() contains a period other than at the beginning and but does not consist solely of one or two periods, returns the substring of filename() starting at its beginning and ending with the character before the last period. Otherwise, returns filename().

Change 27.10.8.4.9 [path.decompose] ¶ 10:

path extension() const;

Returns: if filename() contains a period other than at the beginning and but does not consist solely of one or two periods, returns the substring of filename() starting at the rightmost period and for the remainder of the path. Otherwise, returns an empty path object.

Beman Dawes supplied the above wording per the LEWG vote. It has not been reviewed by the small group.

US 62; 27.10.8.4.9 [path.decompose] ¶13 (was ¶11): It is important that stem()+extension()==filename()
Status: Reject

Yes, it is important. But the note in ¶13 already says exactly that, so the question becomes "Should we make that part of the note normative?"

Saying that normatively would be a second way of saying what is already specified behavior, and saying the same normative thing twice is not good standardese. No proposed wording.

US 63; 27.10.8.4.11 [path.gen] ¶1: lexically_normal() inconsistently treats trailing "/" but not "/.." as directory
Status: Accept with modifications

See US-37 and the change to [path.gen] in US-74/CA-3.

US 185; 27.10.7 [fs.err.report]: Fold error_code and non-error_code signatures into one signature
Status: Reject

Does not handle one signature being noexcept(true) and the other noexcept(false), and many other problems. Even the submitter is no longer in favor. See LWG mailing list thread "[filesystem] US-185 Eliminating dual signatures for operational functions", October 25, 2016.

FI 14; 27.10.12.3 [directory_entry.obs]: directory_entry comparisons are members
Status: Reject

This is LWG issue 2761, which has been closed as NAD.

US 73, CA 2; 27.10.8.1 [path.generic]: root-name is effectively implementation defined
Status: Accept with modifications

Change [path.generic]:

root-name:
An operating system dependent name that identifies the starting location for absolute paths. If the operating system does not define at least one root-name, then the implementation defines a root-name. Implementations are permitted to define additional root-names. [ Note: Many operating systems define a name beginning with two directory-separator characters as a root-name that identifies network or other resource locations. Some operating systems define a single letter followed by a colon as a drive specifier – a root-name identifying a specific device such as a disk drive. —end note ]

Add a new paragraph at the end of [path.generic]:

If root-name is otherwise ambiguous, the possibility with the longest sequence of characters is chosen. [ Note: on a POSIX-like operating system, it is impossible to have a root-name and a relative-path without an intervening root-directory element. -- end note ]

US 74, CA 3; 27.10.8 [class.path]: The term “pathname” is ambiguous in some contexts
Status: Accept with modifications

Davis Herring supplied the wording at the request of the filesystem small group in Issaquah. The wording has been reviewed by Beman Dawes but not the rest of the small group.

This NB comment is a showstopper for C++17. These specification improvements enable the resolution of many other filesystem NB comments.

Discussion:

Many operations on filesystem::path are defined in terms of its exposition-only pathname member, which is defined implicitly by path::native() as the native format path. However, the native format need not be compatible with lexical operations like, for example, path::root_name() and path::extension().

This same concern was also raised by P0430R0 Section 2.1, which provided additional rationale.

The proposed resolution below clarifies the distinct role played by the += operator as mentioned in US 44 and addresses US 74/CA 3 (with a more extensive resolution).

Proposed resolution:

Remove In the [class.path] synopsis, remove the private (exposition-only) member from class path:

private:
  string_type pathstring; // exposition only

Change [path.fmt.cvt]:

Option A; from Davis:

[ Note: The format conversions described in this section are not applied on POSIX- or Windows-based operating systems because on these systems:

— The generic format is acceptable as a native path.
— There is no need to distinguish between native format and generic format in function arguments.
— Paths for regular files and paths for directories share the same syntax.

—end note ]

Option B; from Beman:

[ Note: The format conversions described in this section are usually not applied on POSIX- or Windows-based operating systems because on these systems:

— The generic format is acceptable as a native path.
— There is usually no need to distinguish between native format and generic format in function arguments.
— Paths for regular files and paths for directories share the same syntax.

Even on these operating systems, the format conversions may be applied for pathnames with implementation-defined root-names ([path.generic]).

—end note ]

We need to choose between Option A or Option B.

Several functions are defined to accept detected-format character sequence arguments that represent paths using either the generic pathname format grammar ([path.generic]) or the native pathname format ([fs.def.native]). Such an argument is taken to be in the generic format if and only if it matches the generic format but is not acceptable to the operating system as a native path.

Function arguments that take character sequences representing paths may use the generic pathname format grammar (27.10.8.1) or the native pathname format (27.10.4.11). If and only if such arguments are in the generic format and the generic format is not acceptable to the operating system as a native path, conversion to native format shall be performed during the processing of the argument.

[ Note: Some operating systems may have no unambiguous way to distinguish between native format and generic format arguments. This is by design as it simplifies use for operating systems that do not require disambiguation. An implementation for an operating system where disambiguation is required is permitted to distinguish between the formats. —end note ]

Beman says his code font markup of text from Davis in the following paragraph is almost certainly wrong:

• Would s/Define G(n) and N(g) as the functions/Let G and N be the implementation's functions/ be clearer?

• Are some of the '=' supposed to be '=='?

Pathnames are converted as needed between the generic and native formats in an operating-system-dependent manner. Define G(n) and N(g) as the functions that convert to the generic and native formats respectively. If g=G(n) for some n, then G(N(g))=g; if n=N(g) for some g, then N(G(n))=n. [ Note: Neither G nor N need be invertible. —end note ]

If the native format requires paths for regular files to be formatted differently from paths for directories, the path shall be treated as a directory path if its last element is a directory-separator, otherwise it shall be treated as a path to a regular file.

When a path is constructed from or is assigned a single representation separate from any path, the other representation is selected by the appropriate conversion function (G or N).

When the (new) value p of one representation of a path is derived from the representation of that or another path, a value q is chosen for the other representation. The value q converts to p (by G or N as appropriate) if any such value does so; q is otherwise unspecified. [ Note: If q is the result of converting any path at all, it is the result of converting p.—end note ]

[SG note: P0430R1 (for US 75/CA 4) adds support for explicitly specifying the format to use, at least in the constructor.]

Change [path.construct]:

path(const path& p);
path(path&& p) noexcept;

Effects: Constructs an object of class path having the same native and generic format pathnames as p with pathstring having the original value of p.pathstring. In the second form, p is left in a valid but unspecified state.

path(string_type&& source);

Effects: Constructs an object of class path for which the pathname in the detected-format  of source has with pathstring having the original value of source ([path.fmt.cvt]). source is left in a valid but unspecified state.

template <class Source>
path(const Source& source);
template <class InputIterator>
path(InputIterator first, InputIterator last);

Effects: Let s be the effective range of source ([path.req]) or the range [first, last), with the encoding converted if required ([path.cvt]). Finds the detected-format of s ([path.fmt.cvt]) and constructs an object of class path for which the pathname in that format is s.  Constructs an object of class path, storing the effective range of source (27.10.8.3) or the range [first, last) in pathstring, converting format and encoding if required (27.10.8.2).

template <class Source>
path(const Source& source, const locale& loc);
template <class InputIterator>
path(InputIterator first, InputIterator last, const locale& loc);

Requires: The value type of Source and InputIterator is char.

 Effects:  Constructs an object of class path, storing the effective range of source or the range [first, last) in pathstring, after converting format if required and Let s be the effective range of source or the range [first, last), after converting the encoding as follows:

— If value_type is wchar_t, converts to the native wide encoding (27.10.4.10) using the codecvt<wchar_t, char, mbstate_t> facet of loc.

 — Otherwise a conversion is performed using the codecvt<wchar_t, char, mbstate_t> facet of loc, and then a second conversion to the current narrow encoding.

Finds the detected-format of s ([path.fmt.cvt]) and constructs an object of class path for which the pathname in that format is s.

In the example after [path.fmt.cvt] ¶ 7.2, change:

For POSIX-based operating systems, the path is constructed by first using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a wide character string in the native wide encoding (27.10.4.10). The resulting wide string is then converted to a narrow character pathstring pathname string in the current native narrow encoding. If the native wide encoding is UTF-16 or UTF-32, and the current native narrow encoding is UTF-8, all of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation, but for other native narrow encodings some characters may have no representation.

For Windows-based operating systems, the path is constructed by using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a UTF-16 encoded wide character pathstring pathname string. All of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation.

Change [path.assign]:

path& operator=(const path& p);

Effects: If *this and p are the same object, has no effect. Otherwise, sets the native and generic format pathnames to those of p modifies pathstring to have the original value of p.pathstring.

Returns: *this.

path& operator=(path&& p) noexcept;

Effects: If *this and p are the same object, has no effect. Otherwise, sets the native and generic format pathnames to those of p modifies pathstring to have the original value of p.pathstring. p is left in a valid but unspecified state. [ Note: A valid implementation is swap(p). —end note ]

Returns: *this.

path& operator=(string_type&& source);
path& assign(string_type&& source);

Effects: Sets the native and generic format pathnames to those of source Modifies pathstring to have the original value of source. source is left in a valid but unspecified state.

Returns: *this.

template <class Source>
path& operator=(const Source& source);
template <class Source>
path& assign(const Source& source);
template <class InputIterator>
path& assign(InputIterator first, InputIterator last);

Effects: Let s be the effective range of source ([path.req]) or the range [first, last), with the encoding converted if required ([path.cvt]). Finds the detected-format of s and sets the pathname in that format to s ([path.fmt.cvt]). Stores the effective range of source (27.10.8.3) or the range [first, last) in pathstring, converting format and encoding if required (27.10.8.2).

Returns: *this.

path& operator/=(const path& p);

Effects: If equivalent to has_filename() || !has_root_directory() && is_absolute(), then appends path::preferred_separator to the generic format pathname. [ Example: path("//host")/"foo" and path("//host/")/"foo" both equal "//host/foo". —end example ]

 Appends path::preferred_separator to pathstring unless:

— an added directory-separator would be redundant, or

— an added directory-separator would change a relative path into an absolute path [Note: An empty path is relative.—end note ] , or

— p.empty() is true, or

— *p.native().cbegin() is a directory-separator.

Then appends p.native() to the native format pathname  pathstring.

Returns: *this.

[SG note: this proposed wording depends on LWG 2732 and the recently proposed definition of has_filename() and will change again to address LWG 2664 and US 77/CA 6. It already, simply by ignoring p entirely until such time, addresses US 51.]

Change [path.modifiers]:

path& make_preferred();

Effects: Each directory-separator is converted to preferred-separator in the generic format pathname.

[SG note: the existing definition of remove_filename() is broken; it is expected to be rewritten.]

Change [path.modifiers]:

path& replace_extension(const path& replacement = path());

Effects: pathstring (the stored path) is modified as follows:

— Any existing extension()(27.10.8.4.9) is removed from the generic format pathname stored path, then

— If replacement is not empty and does not begin with a dot character, a dot character is appended to the generic format pathname stored path, then

— operator+=(replacement); replacement is concatenated to the stored path.

Returns *this.

Change [path.modifiers]:

void swap(path& rhs) noexcept;

Effects: Swaps the contents (in all formats) of the two paths pathstring and rhs.pathstring.

Change [path.native.obs]:

const string_type& native() const noexcept;

Returns: The native format pathname pathstring.

const value_type* c_str() const noexcept;

Returns: Equivalent to native().c_str() pathstring.c_str().

operator string_type() const;

Returns: native() pathstring.

[ Note: Conversion to string_type is provided so that an object of class path can be given as an argument to existing standard library file stream constructors and open functions. —end note ]

template <class EcharT, class traits = char_traits<EcharT>,
          class Allocator = allocator<EcharT>>
  basic_string<EcharT, traits, Allocator>
    string(const Allocator& a = Allocator()) const;

Returns: native() pathstring.

Remarks: All memory allocation, including for the return value, shall be performed by a. Conversion, if any, is specified by 27.10.8.2.

Change [path.generic.obs]:

template <class EcharT, class traits = char_traits<EcharT>,
          class Allocator = allocator<EcharT>>
  basic_string<EcharT, traits, Allocator>
    generic_string(const Allocator& a = Allocator()) const;

Returns: The generic format pathname pathstring, reformatted according to the generic pathname format (27.10.8.1).

Remarks: All memory allocation, including for the return value, shall be performed by a. Conversion, if any, is specified by 27.10.8.2.

std::string generic_string() const;
std::wstring generic_wstring() const;
std::string generic_u8string() const;
std::u16string generic_u16string() const;
std::u32string generic_u32string() const;

Returns: The generic format pathname pathstring, reformatted according to the generic pathname format (27.10.8.1).

Remarks: Conversion, if any, is specified by 27.10.8.2. The encoding of the string returned by generic_u8string() is always UTF-8.

Change [path.decompose]:

path root_name() const;

Returns: root-name, if the generic format pathname pathstring includes root-name, otherwise path().

path root_directory() const;

Returns: root-directory, if the generic format pathname pathstring includes root-directory, otherwise path().

...

path relative_path() const;

Returns: A path composed from the generic format pathname pathstring, if !empty(), beginning with the first filename after root-path. Otherwise, path().

...

path filename() const;

Returns: relative_path().empty() ? path() : *--end().

[ Example:

std::cout << path("/foo/bar.txt").filename(); // outputs "bar.txt"
std::cout << path("/foo/bar").filename();     // outputs "bar"
std::cout << path("/foo/bar/").filename();    // outputs ""
std::cout << path("/").filename();            // outputs "/"
std::cout << path("//host").filename();       // outputs ""
std::cout << path(".").filename();            // outputs "."
std::cout << path("..").filename();           // outputs ".."

—end example ]

path stem() const;

Returns: if filename() contains a period but does not consist solely of one or two periods, returns the substring of filename() starting at its beginning and ending with the character before the last period. Otherwise, returns filename().

Returns: Let f be the generic format pathname for filename(). Returns a path whose generic format pathname is

- f, if it contains no periods other than a leading period or consists solely of one or two periods;

- otherwise, the prefix of f ending before its last period.

Beman Dawes inserted "other than a leading period" to reflect LEWG guidance from Issaquah. That wording has not been reviewed by the filesystem small group.

[ Example:

std::cout << path("/foo/bar.txt").stem(); // outputs "bar"
path p = "foo.bar.baz.tar";
for (; !p.extension().empty(); p = p.stem())
std::cout << p.extension() << ’\n’;
// outputs: .tar
// .baz
// .bar

—end example ]

path extension() const;

Returns: a path whose generic format pathname is the suffix of the generic format pathname for filename() not included in stem(). if filename() contains a period but does not consist solely of one or two periods, returns the substring of filename() starting at the rightmost period and for the remainder of the path. Otherwise, returns an empty path object.

Remarks: Implementations are permitted to define additional behavior for file systems which append additional elements to extensions, such as alternate data streams or partitioned dataset names.

[ Example:

std::cout << path("/foo/bar.txt").extension(); // outputs ".txt"
std::cout << path("/foo/bar").extension();     // outputs ""

—end example ]

[ Note: The period is included in the return value so that it is possible to distinguish between no extension and an empty extension. Also note that for a path p, p.stem()+p.extension() == p.filename(). —end note ]

Change [path.query]:

bool empty() const noexcept;

Returns: true if the generic format pathname is empty, else false pathstring.empty().

...

bool is_absolute() const;

Returns: true if the native format pathname pathstring contains an absolute path (27.10.4.1), else false.

[ Example: path("/").is_absolute() is true for POSIX-based operating systems, and false for Windows-based operating systems. —end example ]

Change [path.gen]:

path lexically_normal() const;

Returns: a path whose generic format pathname is the normal form ([fs.def.normal.form]) of the generic format pathname of *this *this in normal form ([fs.def.normal.form]).

[ Example:
    assert(path("foo/./bar/..").lexically_normal() == "foo");
    assert(path("foo/.///bar/../").lexically_normal() == "foo/.");

The above assertions will succeed. The second example ends with a current directory (dot) element appended to support operating systems that use different syntax for directory names and regular file names.

On Windows, the returned path’s directory-separator characters will be backslashes rather than slashes, but that does not affect path equality. —end example ]

Change [path.itr]:

Path iterators iterate over the elements of the generic format pathname pathstring in the generic format (27.10.8.1).

A path::iterator is a constant iterator satisfying all the requirements of a bidirectional iterator (24.2.6) except that, for dereferenceable iterators a and b of type path::iterator with a == b, there is no requirement that *a and *b are bound to the same object. Its value_type is path.

Calling any non-const member function of a path object invalidates all iterators referring to elements of that object.

For the elements of the generic format pathname pathstring in the generic format, the forward traversal order is as follows:

...

Change [fs.op.canonical]:

path canonical(const path& p, error_code& ec);
path canonical(const path& p, const path& base, error_code& ec);

Effects: Converts p, which must exist, to an absolute path that has no symbolic link, dot, or dot-dot elements in its generic format pathname ".", or ".." elements.

...

Change [fs.op.current_path]:

path current_path();
path current_path(error_code& ec);

Returns: The absolute path of the current working directory, obtained in the native format as if by POSIX getcwd(). The signature with argument ec returns path() if an error occurs.

...

Rationale:

The lexical operation specifications leave some room for variation among implementations, but not as much as may be required for native formats; further relaxation would compromise the utility of the operations for portable, predictable path manipulation. Instead, we specify a usable but flexible mapping between the two formats and define each operation in terms of one (or, occasionally, both).

The second bullet item in the first note in [path.fmt.cvt], which says for POSIX- or Windows-based operating systems "There is no need to distinguish between native format and generic format in function arguments.", may not be true on Windows even if the other two bullet items are true.

US 75, CA 4; 27.10.8.4.1 [path.construct]: Extra flag in path constructors is needed
Status: Accept with modifications

See P0430R1 Section 2.2 for wording.

US 76, CA 5; 27.10.8.1 [path.generic]: root-name definition is over-specified
Status: Accept with modifications

See P0430R1 Section 2.3.1 for wording.

US 77, CA 6; 27.10.8.4.3 [path.append]: operator/ and other appends not useful if arg has root-name
Status: Accept with modifications

See P0430R1 Section 2.3.2 for wording.

US 78, CA 7; 27.10.15.1 [fs.op.absolute]: Member absolute() in 27.10.4.1 is overspecified for non-POSIX-like O/S
Status: Accept with modifications

See P0430R1 Section 2.4.1 for wording.

US 79, CA 8; Several: Some operation functions are overspecified for implementation-defined file types
Status: Accept with modifications

See P0430R1 Section 2.4.2 for wording.

NB comments submitted as editorial

There was concern that some of these might involve substantive changes, so the SG processed them as ordinary technical comments.

US 38; 27.10.4.13 [fs.def.symlink]:  Duplicates §17.3.16
Status: Accept

Project editor will make change.

US 39; 27.10.4.15 [fs.def.parent]: Remove note: Dot and dot-dot are not directories
Status: Accept

Project editor will make change.

US 41; 27.10.4.16 [fs.def.parent.other]: The term “parent directory” for a (non-directory) file is unusual
Status: Reject

Insufficient motivation for change. "parent directory" is the term we use to describe the containing directory; we're (already) following POSIX there, even though the POSIX definition is a bit weird.

US 42; 27.10.4.21 [fs.def.symlink]: Pathname resolution does not always resolve a symlink
Status: Reject

There is an apparent corner case contradiction between the POSIX definition and other places in the POSIX standard. The [fs.def.symlink] definition is identical to the POSIX 3.381 Symbolic Link definition () and the SG prefers to keep it that way.

US 47; 27.10.8.1 [path.generic]: “.” and “..” already match the name production
Status: Accept with modifications

This is not editorial, but we know the fix. Davis Herring to supply updated proposed wording.

US 50;  27.10.8.3 [path.req]: path requirements ¶ 1.4 largely redundant with ¶ 1.3
Status: Reject

Beman Dawes to open an issue to expose this concern to additional experts. This is not a priority issue for shipping C++17.

Late comments from P0489R0

Quoting P0489R0, "These comments were not submitted in time to be registered as National Body Comments, but should be considered as possible issues against SC 22, N3151, ISO/IEC CD 14882."

Late 15; 27.10.8.4.11 ¶3.1: A “mismatched element” cannot be equal to an iterator

Late 16; 27.10.8.4.11 ¶3.3.1: lexically_relative("..\\foo") produces nonsense.

Late 17; 27.10.8.4.11 ¶3.3.2: Behavior not always appropriate

Late 18; 27.10.8.4.11 ¶4: Behavior wrong in case corresponding to comment Late17

Late 19; 27.10.8.5 ¶2: It is surprising that a path is a container of paths

Recommend NAD. See US 55, US 59.

Late 20; 27.10.11 ¶1: Anemic status structure

Late 21; 27.10.12: directory_entry is just a trivial wrapper for path

Subsumed by LWG 2663 and 2677

Late 22; 27.10.13 ¶6: directory_iterator cumbersome to assemble full path with iterator’s directory

Late 23; 27.10.14.1 ¶28: disable_recursion_pending() name is ugly implementation detail

Late 24; 27.10.15.1 ¶1: absolute() can produce nonsense result

Late 25; 27.10.15.4 ¶4.2: What attributes does copy_file() copy?

Late 26; 27.10.15.6 ¶5: create_directories() complexity assumes syscalls take constant time

Late 27; 27.10.15.7 ¶5: create_directory() specification prevents sensible security measures

Late 28; 27.10.15.10: create_symlink() might misbehave if to is a directory

Late 29; 27.10.15.13: Access to file ID is superior to equivalent()

Late 30; 27.10.15.13 ¶3: equivalent()'s s1==s2 check is ill-formed and could race

Late 31; 27.10.15.13 ¶5: Surprising that equivalent()'s error_code overload can throw

Late 32; 27.10.15.13 ¶5 : equivalent() should not reject special files outright

Late 33; 27.10.15.21: is_other() result surprising

Late 34; 27.10.15.25 ¶5: Could last_write_time() guarantee the error direction

Recommend submitting a paper that researches whether this is in fact possible. If it is possible, providing proposed wording would be helpful.

Late 35; 27.10.15.26: Why is there no way to read permissions?

Recommend NAD. They are available in file_status. If anyone thinks a separate function would be useful, they should submit an issue or a paper.

Late 36; 27.10.15.26: The permissions() error_code overload should be noexcept
Status: Accept

Change 27.10.15.26 [fs.op.permissions] and 27.10.6 Header <filesystem> synopsis [fs.filesystem.syn]:

void permissions(const path& p, perms prms, error_code& ec) noexcept;

Late 37; 27.10.15.26 ¶2:permissions() actions should be separate parameter
Status: Accept with modifications

Beman Dawes supplied the wording, which has been reviewed by Davis but not others. Beman comments: Matt Austern pointed this out, with the same suggested fix, prior to the TS. It got dropped on the floor in the TS shipping rush and has never been fixed. It is an embarrassment that needs fixing before shipping C++17.

Change [fs.filesystem.syn]:

// 27.10.10, enumerations
enum class file_type;
enum class perms;
enum class perm_options;
enum class copy_options;
enum class directory_options;

...

void permissions(const path& p, perms prms, perm_options opts=perm_options::replace);
void permissions(const path& p, perms prms, error_code& ec);
void permissions(const path& p, perms prms, perm_options opts, error_code& ec);

Strike the following rows in [fs.enum] Table nnn — Enum class perms:

• add_perms
• remove_perms
• symlink_nofollow

Insert a new sub-section after [enum.perms]:

27.10.n.n Enum class perm_options [enum.perm_options]

The enum class type perm_options is a bitmask type (bitmask.types) that specifies bitmask constants used to control the semantics of permissions operations.

Table nnn — Enum class perm_options

Name	Meaning
replace	(Default) permissions() shall replace the file's permission bits with the perm argument’s permission bits.
add	permissions() shall bitwise or the perm argument’s permission bits to the file’s current permission bits.
remove	permissions() shall bitwise and the complement of the perm argument’s permission bits to the file’s current permission bits.
nofollow	permissions() shall change the permissions of a symbolic link itself rather than the permissions of the file the link resolves to. nofollow is a bit-mask value.

Change [fs.op.permissions]:

void permissions(const path& p, perms prms, perm_options opts=perm_opts::replace);
void permissions(const path& p, perms prms, error_code& ec);
void permissions(const path& p, perms prms, perm_options opts, error_code& ec);

Requires: !((prms & perms::add_perms) != perms::none && (prms & perms::remove_perms) != perms::none). One and only one of the perm_options constants replace, add, or remove is present in opts.

Remarks: The second signature behaves as if it had an additional argument  perm_options opts with a value of perm_options::replace.

Effects: Applies the effective permissions bits from prms to the file p resolves to, or if that file is a symbolic link and symlink_nofollow is not set in prms, the file that it points to, as if by POSIX fchmodat(). The effective permission bits are determined as specified in Table 127, where s is the result of (prms & perms::symlink_nofollow) != perms::none ? symlink_status(p) : status(p).

Effects: Applies the action specified by opts to the file p resolves to, or to file p itself if p is a symbolic link and perm_options::nofollow is set in opts. The action is applied as if by POSIX fchmodat().

[ Note: Conceptually permissions are viewed as bits, but the actual implementation may use some other mechanism. —end note ]

Throws: As specified in 27.10.7.

Late 38; 27.10.15.26 ¶2: Unimplementable implication that permissions() is atomic

Late 39; 27.10.15.29 ¶3: Suprising relative() behavior for symlinks

Late 40; 27.10.15.31 ¶1: remove_all() unclear for symlink/

Late 41; 27.10.15.31 ¶3: Would be useful for remove_all() to report successful removal count on error

Late 42; 27.10.15.33 ¶1: resize_file() Postcondition missing argument
Status: Editorial

Fixed in the post-Issaquah working paper

Late 43; 27.10.15.33 ¶3: Add POSIX ftruncate() equivalent function

Recommend opening issue. Such a feature might be useful in 27.9 [file.streams] for C++2n.

Late 44; 27.10.15.38: system_complete() name inconsistent with similar functions in subclause

Late 45; 27.10.15.38 ¶6: Remove system_complete() unless it can be made reliable

Late 46; 27.10.15.40 ¶2: Question about weakly_canonical() Effects

Late 47; 27.10.15.40 ¶4: weakly_canonical() suggested caching is incorrect