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, 16 insertions, 5 deletions

diff --git a/src/lread.c b/src/lread.c
index 6ae7a0d8ba0..d8883db46c1 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -1346,15 +1346,22 @@ Return t if the file exists and loads successfully.  */)
           if (!load_prefer_newer && is_elc)
             {
               result = stat (SSDATA (efound), &s1);
+              int err = errno;
               if (result == 0)
                 {
                   SSET (efound, SBYTES (efound) - 1, 0);
                   result = stat (SSDATA (efound), &s2);
+                  err = errno;
                   SSET (efound, SBYTES (efound) - 1, 'c');
+                  if (result != 0)
+                    found = Fsubstring (found, make_fixnum (0),
+                                        make_fixnum (-1));
                 }
-
-              if (result == 0
-                  && timespec_cmp (get_stat_mtime (&s1), get_stat_mtime (&s2)) < 0)
+              if (result != 0)
+                file_attribute_errno (found, err);
+              else if (timespec_cmp (get_stat_mtime (&s1),
+                                     get_stat_mtime (&s2))
+                       < 0)
                 {
                   /* Make the progress messages mention that source is newer.  */
                   newer = 1;
@@ -1748,16 +1755,20 @@ openp (Lisp_Object path, Lisp_Object str, Lisp_Object suffixes,
                   {
                     if (file_directory_p (encoded_fn))
                       last_errno = EISDIR;
-                    else
+                    else if (errno == ENOENT || errno == ENOTDIR)
                       fd = 1;
+                    else
+                      last_errno = errno;
                   }
+                else if (! (errno == ENOENT || errno == ENOTDIR))
+                  last_errno = errno;
               }
             else
               {
                 fd = emacs_open (pfn, O_RDONLY, 0);
                 if (fd < 0)
                   {
-                    if (errno != ENOENT)
+                    if (! (errno == ENOENT || errno == ENOTDIR))
                       last_errno = errno;
                   }
                 else