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, 4 insertions, 5 deletions

diff --git a/src/dired.c b/src/dired.c
index df03bc32cef..3768b6dbb7c 100644
--- a/src/dired.c
+++ b/src/dired.c
@@ -819,7 +819,7 @@ stat_gname (struct stat *st)
 
 DEFUN ("file-attributes", Ffile_attributes, Sfile_attributes, 1, 2, 0,
        doc: /* Return a list of attributes of file FILENAME.
-Value is nil if specified file cannot be opened.
+Value is nil if specified file does not exist.
 
 ID-FORMAT specifies the preferred format of attributes uid and gid (see
 below) - valid values are `string' and `integer'.  The latter is the
@@ -939,15 +939,14 @@ file_attributes (int fd, char const *name,
 	 information to be accurate.  */
       w32_stat_get_owner_group = 1;
 #endif
-      if (fstatat (fd, name, &s, AT_SYMLINK_NOFOLLOW) == 0)
-	err = 0;
+      err = fstatat (fd, name, &s, AT_SYMLINK_NOFOLLOW) == 0 ? 0 : errno;
 #ifdef WINDOWSNT
       w32_stat_get_owner_group = 0;
 #endif
     }
 
   if (err != 0)
-    return unbind_to (count, Qnil);
+    return unbind_to (count, file_attribute_errno (filename, err));
 
   Lisp_Object file_type;
   if (S_ISLNK (s.st_mode))
@@ -956,7 +955,7 @@ file_attributes (int fd, char const *name,
 	 symlink is replaced between the call to fstatat and the call
 	 to emacs_readlinkat.  Detect this race unless the replacement
 	 is also a symlink.  */
-      file_type = emacs_readlinkat (fd, name);
+      file_type = check_emacs_readlinkat (fd, filename, name);
       if (NILP (file_type))
 	return unbind_to (count, Qnil);
     }