2659. [filesys.ts] [PDTS] Invalid expressions for bitmask types

Section: 10 [filesys.ts::fs.enum] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2014-03-01 Last modified: 2016-08-11

Priority: Not Prioritized

View all issues with NAD Editorial status.

Discussion:

Addresses: filesys.ts

copy_options is declared as enum class type that is a bismask type, but the specification repeatedly uses expressions that are invalid for scoped enums, such as:

!(options)

because there is no contextual conversion to bool, not even the || operator in:

((options & copy_options::recursive) || !(options))

Affected are basically all formulations in the form:

"if options & copy_options::create_symlinks [..]"

because all rely on contextual conversion to bool. The only other specifically mention scoped enumeration in the standard that is also a bit mask type is the launch enum and the wording there always uses forms such as:

"if policy & launch::deferred is non-zero"

which better acknowledges the fact that the obtained values does not necessarily undergo an implicit conversion.

I think the current wording in the file system spec. must be changed, especially for invalid expressions of the form:

((options & copy_options::recursive) || !(options))

A similar problem arises in the usage of the bitmask type perms for the expression:

((prms & add_perms) && (prms & remove_perms))

The only way how to describe this with a scoped enum is the lengthier form

((prms & perms::add_perms) != perms::none && (prms & perms::remove_perms) != perms::none)

thus fixing several problems:

• The unscoped access to add_perms and remove_perms is incorrect
• The result of & is the bitmask type again and cannot be implicitly converted to bool

[20 May 2014 Beman Dawes provides proposed wording. Fixing invalid C++ is editorial, but treating this as an issue ensures more people review the proposed changes.]

[17 Jun 2014 Rapperswil LWG requests issue be handled as editorial.]

Proposed resolution:

Change 15.3 Copy [fs.op.copy]:

Before the first use of f and t:

• If (options & copy_options::create_symlinks) != copy_options::none || (options & copy_options::skip_symlinks) != copy_options::none, then auto f = symlink_status(from) and if needed auto t = symlink_status(to).
• Otherwise, auto f = status(from) and if needed auto t = status(to) .

Report an error as specified in Error reporting (7) if:

• !exists(f), or
• equivalent(from, to), or
• is_other(f) || is_other(t), or
• is_directory(f) && is_regular_file(t).

If is_symlink(f), then:

• If (options & copy_options::skip_symlinks) != copy_options::none, then return.
• Otherwise if !exists(t), then copy_symlink(from, to, options) .
• Otherwise report an error as specified in Error reporting (7).

Otherwise if is_regular_file(f), then:

• If (options & copy_options::directories_only) != copy_options::none, then return.
• Otherwise if (options & copy_options::create_symlinks ) != copy_options::none, then create a symbolic link to the source file.
• Otherwise if (options & copy_options::create_hard_links) != copy_options::none, then create a hard link to the source file.
• Otherwise if is_directory(t), then copy_file(from, to/from.filename(), options) .
• Otherwise, copy_file(from, to, options).

Otherwise if is_directory(f) && ((options & copy_options::recursive) != copy_options::none || !(options == copy_options::none)) then:

• If  !exists(t), then create_directory(to, from) .
• Then, iterate over the files in from, as if by for (directory_entry& x : directory_iterator(from)) , and for each iteration copy(x.path(), to/x.path().filename(), options | copy_options::unspecified) .

Change 15.4 Copy file [fs.op.copy_file]:

If  exists(to) && !(options & (copy_options::skip_existing | copy_options::overwrite_existing | copy_options::update_existing)) == copy_options::none report a file already exists error as specified in Error reporting (7).

If !exists(to) || (options & copy_options::overwrite_existing) != copy_options::none || ((options & copy_options::update_existing) != copy_options::none && last_write_time(from) > last_write_time(to)) || !(options & (copy_options::skip_existing | copy_options::overwrite_existing | copy_options::update_existing)) == copy_options::none copy the contents and attributes of the file from resolves to the file to resolves to.

Change 15.26 Permissions [fs.op.permissions]:

Requires: !((prms & perms::add_perms) != perms::none && (prms & perms::remove_perms) != perms::none).