Improve reporting of I/O, access errors

Signal an error for file-oriented errors that are not tame
errors like ENOENT and ENOTDIR (Bug#37389).
Do this for primitives exposed to Lisp; the lower
level internal C API merely makes errno values available
to higher-level C code.
* doc/lispref/files.texi (Testing Accessibility)
(File Attributes, Extended Attributes): Do not say that the
functions return nil when the return value cannot be determined.
* etc/NEWS: Mention the change.
* src/dired.c (Ffile_attributes): Fix doc string confusion
about opening a file vs getting its attributes.
(file_attributes): Signal serious errors.
* src/fileio.c (check_existing, check_executable)
(check_writable): Remove.  All callers changed to use
check_file_access or file_access_p.
(file_access_p, file_metadata_errno, file_attribute_errno)
(file_test_errno, check_file_access, check_emacs_readlinkat):
New functions.
* src/fileio.c (Ffile_executable_p, Ffile_readable_p)
(Ffile_name_case_insensitive_p, Frename_file, Ffile_exists_p):
(Ffile_symlink_p, Ffile_directory_p)
(Ffile_accessible_directory_p, Ffile_regular_p)
(Ffile_selinux_context, Ffile_acl, Ffile_modes)
(Ffile_newer_than_file_p, Fset_visited_file_modtime)
(Ffile_system_info):
* src/filelock.c (unlock_file, Ffile_locked_p):
* src/lread.c (Fload):
Signal serious errors.
* src/fileio.c (Ffile_writable_p): Remove unnecessary CHECK_STRING.
(emacs_readlinkat): Now static.
* src/filelock.c (current_lock_owner, lock_if_free): Return a
positive errno on error, and the negative of the old old value
on success.  All callers changed.
* src/lread.c (openp): Propagate serious errno values to caller.

1 files changed, 5 insertions, 8 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 18a1f4908d6..fba9622fecf 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -856,8 +856,7 @@ systems, this is true if the file exists and you have execute
 permission on the containing directories, regardless of the
 permissions of the file itself.)
 
-If the file does not exist, or if access control policies prevent you
-from finding its attributes, this function returns @code{nil}.
+If the file does not exist, this function returns @code{nil}.
 
 Directories are files, so @code{file-exists-p} can return @code{t} when
 given a directory.  However, because @code{file-exists-p} follows
@@ -1262,7 +1261,7 @@ on the 19th, @file{aug-20} was written on the 20th, and the file
 @defun file-attributes filename &optional id-format
 @anchor{Definition of file-attributes}
 This function returns a list of attributes of file @var{filename}.  If
-the specified file's attributes cannot be accessed, it returns @code{nil}.
+the specified file does not exist, it returns @code{nil}.
 This function does not follow symbolic links.
 The optional parameter @var{id-format} specifies the preferred format
 of attributes @acronym{UID} and @acronym{GID} (see below)---the
@@ -1464,9 +1463,8 @@ The underlying ACL implementation is platform-specific; on GNU/Linux
 and BSD, Emacs uses the POSIX ACL interface, while on MS-Windows Emacs
 emulates the POSIX ACL interface with native file security APIs.
 
-If Emacs was not compiled with ACL support, or the file does not exist
-or is inaccessible, or Emacs was unable to determine the ACL entries
-for any other reason, then the return value is @code{nil}.
+If ACLs are not supported or the file does not exist,
+then the return value is @code{nil}.
 @end defun
 
 @defun file-selinux-context filename
@@ -1478,8 +1476,7 @@ for details about what these actually mean.  The return value has the
 same form as what @code{set-file-selinux-context} takes for its
 @var{context} argument (@pxref{Changing Files}).
 
-If Emacs was not compiled with SELinux support, or the file does not
-exist or is inaccessible, or if the system does not support SELinux,
+If SELinux is not supported or the file does not exist,
 then the return value is @code{(nil nil nil nil)}.
 @end defun