Revert too-picky file-access tests

Problem reported by Andreas Schwab (Bug#37475).
* doc/lispref/files.texi (Writing to Files)
(Testing Accessibility, Kinds of Files):
Document that accessibility and file-type predicates return nil
if there is trouble determining accessibility or type.
* etc/NEWS: Adjust, and list the affected primitives.
* src/callproc.c (init_callproc): Go back to Ffile_exists_p.
* src/fileio.c (PICKY_EACCES, file_test_errno):
Remove.  All uses removed.
(Ffile_name_case_insensitive_p, Ffile_exists_p, Ffile_symlink_p)
(Ffile_directory_p, Ffile_regular_p): Document that these
functions return nil if there is trouble.
(Ffile_name_case_insensitive_p, check_file_access)
(Ffile_writable_p, Ffile_symlink_p, Ffile_directory_p)
(Ffile_accessible_directory_p, Ffile_regular_p)
* src/lread.c (Fload):
Go back to treating trouble in determining the answer as if the
file were missing.
* src/fileio.c (Ffile_newer_than_file_p): Use file_attribute_errno
not file_test_errno, since returning nil is not appropriate when
there are two files to test; e.g., in the rare cases where both
file timestamps have overflowed then neither t nor nil is correct.

6 files changed, 54 insertions, 109 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index fba9622fecf..3746c6d2c95 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -607,8 +607,7 @@ This function appends the contents of the region delimited by
 @var{filename}.  If that file does not exist, it is created.  This
 function returns @code{nil}.
 
-An error is signaled if @var{filename} specifies a nonwritable file,
-or a nonexistent file in a directory where files cannot be created.
+An error is signaled if you cannot write or create @var{filename}.
 
 When called from Lisp, this function is completely equivalent to:
 
@@ -851,12 +850,13 @@ permissions.
 @defun file-exists-p filename
 This function returns @code{t} if a file named @var{filename} appears
 to exist.  This does not mean you can necessarily read the file, only
-that you can find out its attributes.  (On GNU and other POSIX-like
+that you can probably find out its attributes.  (On GNU and other POSIX-like
 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, this function returns @code{nil}.
+If the file does not exist, or if there was trouble determining
+whether the file exists, 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
@@ -881,7 +881,7 @@ inside the directory, and open those files if their modes permit.
 This function returns @code{t} if the file @var{filename} can be written
 or created by you, and @code{nil} otherwise.  A file is writable if the
 file exists and you can write it.  It is creatable if it does not exist,
-but the specified directory does exist and you can write in that
+but its parent directory does exist and you can write in that
 directory.
 
 In the example below, @file{foo} is not writable because the parent
@@ -899,7 +899,7 @@ directory.
 @defun file-accessible-directory-p dirname
 This function returns @code{t} if you have permission to open existing
 files in the directory whose name as a file is @var{dirname};
-otherwise (or if there is no such directory), it returns @code{nil}.
+otherwise (e.g., if there is no such directory), it returns @code{nil}.
 The value of @var{dirname} may be either a directory name (such as
 @file{/foo/}) or the file name of a file which is a directory
 (such as @file{/foo}, without the final slash).
@@ -914,8 +914,8 @@ file in @file{/foo/} will give an error:
 @end defun
 
 @defun access-file filename string
-This function opens file @var{filename} for reading, then closes it and
-returns @code{nil}.  However, if the open fails, it signals an error
+If you can read @var{filename} this function returns @code{nil};
+otherwise it signals an error
 using @var{string} as the error message text.
 @end defun
 
@@ -1011,6 +1011,7 @@ absolute file name of the target; determining the full file name that
 the link points to is nontrivial, see below.)
 
 If the file @var{filename} is not a symbolic link, or does not exist,
+or if there is trouble determining whether it is a symbolic link,
 @code{file-symlink-p} returns @code{nil}.
 
 Here are a few examples of using this function:
@@ -1071,7 +1072,9 @@ link.  If you actually need the file name of the link target, use
 
 @defun file-directory-p filename
 This function returns @code{t} if @var{filename} is the name of an
-existing directory, @code{nil} otherwise.
+existing directory.  It returns @code{nil} if @var{filename} does
+not name a directory, or if there is trouble determining whether
+it is a directory.
 This function follows symbolic links.
 
 @example
@@ -1103,6 +1106,8 @@ This function follows symbolic links.
 This function returns @code{t} if the file @var{filename} exists and is
 a regular file (not a directory, named pipe, terminal, or
 other I/O device).
+It returns @code{nil} if @var{filename} does not exist or is not a regular
+file, or if there is trouble determining whether it is a regular file.
 This function follows symbolic links.
 @end defun
 
diff --git a/etc/NEWS b/etc/NEWS
index cb04da189e5..6a4a6e60d4d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2029,11 +2029,14 @@ longer defaults to 'buffer-file-name'.
 ** File metadata primitives now signal an error if I/O, access, or
 other serious errors prevent them from determining the result.
 Formerly, these functions often (though not always) returned nil.
-For example, if searching /etc/firewalld results in an I/O error,
-(file-symlink-p "/etc/firewalld/firewalld.conf") now signals an error
-instead of returning nil, because file-symlink-p cannot determine
-whether a symbolic link exists there.  These functions still behave as
-before if the only problem is that the file does not exist.
+For example, if there is an access error, I/O error or low-level
+integer overflow when getting the attributes of a file F,
+(file-attributes F) now signals an error instead of returning nil.
+These functions still behave as before if the only problem is that the
+file does not exist.  The affected primitives are
+directory-files-and-attributes, file-acl, file-attributes, file-modes,
+file-newer-than-file-p, file-selinux-context, file-system-info, and
+set-visited-file-modtime.
 
 ---
 ** The function 'eldoc-message' now accepts a single argument.
diff --git a/src/callproc.c b/src/callproc.c
index dbbf15c792a..007465cd405 100644
--- a/src/callproc.c
+++ b/src/callproc.c
@@ -1567,12 +1567,12 @@ init_callproc (void)
 
       tem = Fexpand_file_name (build_string ("NEWS"), Vdata_directory);
       if (!NILP (Fequal (srcdir, Vinvocation_directory))
-          || !file_access_p (SSDATA (tem), F_OK))
+          || NILP (Ffile_exists_p (tem)))
         {
           Lisp_Object newdir;
           newdir = Fexpand_file_name (build_string ("../etc/"), lispdir);
           tem = Fexpand_file_name (build_string ("NEWS"), newdir);
-          if (file_access_p (SSDATA (tem), F_OK))
+          if (!NILP (Ffile_exists_p (tem)))
             Vdata_directory = newdir;
         }
     }
diff --git a/src/fileio.c b/src/fileio.c
index b2896c1fe1e..b510d48dbaa 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -253,30 +253,6 @@ file_attribute_errno (Lisp_Object file, int err)
   return file_metadata_errno ("Getting attributes", file, err);
 }
 
-/* In theory, EACCES errors for predicates like file-readable-p should
-   be checked further because they may be problems with an ancestor
-   directory instead of with the file itself, which means that we
-   don't have reliable info about the requested file.  In practice,
-   though, DOS_NT platforms set errno to EACCES for missing files like
-   "/var/mail", so signaling EACCES errors would be a mistake there.
-   So return nil for EACCES unless PICKY_EACCES, which is false by
-   default on DOS_NT.  */
-#ifndef PICKY_EACCES
-# ifdef DOS_NT
-enum { PICKY_EACCES = false };
-# else
-enum { PICKY_EACCES = true };
-# endif
-#endif
-
-Lisp_Object
-file_test_errno (Lisp_Object file, int err)
-{
-  if (!PICKY_EACCES && err == EACCES)
-    return Qnil;
-  return file_metadata_errno ("Testing file", file, err);
-}
-
 void
 close_file_unwind (int fd)
 {
@@ -2453,7 +2429,9 @@ file_name_case_insensitive_err (Lisp_Object file)
 DEFUN ("file-name-case-insensitive-p", Ffile_name_case_insensitive_p,
        Sfile_name_case_insensitive_p, 1, 1, 0,
        doc: /* Return t if file FILENAME is on a case-insensitive filesystem.
-The arg must be a string.  */)
+Return nil if FILENAME does not exist or is not on a case-insensitive
+filesystem, or if there was trouble determining whether the filesystem
+is case-insensitive.  */)
   (Lisp_Object filename)
 {
   Lisp_Object handler;
@@ -2467,19 +2445,16 @@ The arg must be a string.  */)
   if (!NILP (handler))
     return call2 (handler, Qfile_name_case_insensitive_p, filename);
 
-  /* If the file doesn't exist, move up the filesystem tree until we
-     reach an existing directory or the root.  */
+  /* If the file doesn't exist or there is trouble checking its
+     filesystem, move up the filesystem tree until we reach an
+     existing, trouble-free directory or the root.  */
   while (true)
     {
       int err = file_name_case_insensitive_err (filename);
-      switch (err)
-        {
-        case -1: return Qt;
-        default: return file_test_errno (filename, err);
-        case ENOENT: case ENOTDIR: break;
-        }
+      if (err <= 0)
+        return err < 0 ? Qt : Qnil;
       Lisp_Object parent = file_name_directory (filename);
-      /* Avoid infinite loop if the root is reported as non-existing
+      /* Avoid infinite loop if the root has trouble
          (impossible?).  */
       if (!NILP (Fstring_equal (parent, filename)))
         return Qnil;
@@ -2739,8 +2714,7 @@ file_name_absolute_p (char const *filename)
 }
 
 /* Return t if FILE exists and is accessible via OPERATION and AMODE,
-   nil (setting errno) if not.  Signal an error if the result cannot
-   be determined.  */
+   nil (setting errno) if not.  */
 
 static Lisp_Object
 check_file_access (Lisp_Object file, Lisp_Object operation, int amode)
@@ -2758,22 +2732,13 @@ check_file_access (Lisp_Object file, Lisp_Object operation, int amode)
     }
 
   char *encoded_file = SSDATA (ENCODE_FILE (file));
-  bool ok = file_access_p (encoded_file, amode);
-  if (ok)
-    return Qt;
-  int err = errno;
-  if (err == EROFS || err == ETXTBSY
-      || (PICKY_EACCES && err == EACCES && amode != F_OK
-          && file_access_p (encoded_file, F_OK)))
-    {
-      errno = err;
-      return Qnil;
-    }
-  return file_test_errno (file, err);
+  return file_access_p (encoded_file, amode) ? Qt : Qnil;
 }
 
 DEFUN ("file-exists-p", Ffile_exists_p, Sfile_exists_p, 1, 1, 0,
        doc: /* Return t if file FILENAME exists (whether or not you can read it).
+Return nil if FILENAME does not exist, or if there was trouble
+determining whether the file exists.
 See also `file-readable-p' and `file-attributes'.
 This returns nil for a symlink to a nonexistent file.
 Use `file-symlink-p' to test for such links.  */)
@@ -2834,16 +2799,7 @@ DEFUN ("file-writable-p", Ffile_writable_p, Sfile_writable_p, 1, 1, 0,
      should check ACLs though, which do affect this.  */
   return file_directory_p (encoded) ? Qt : Qnil;
 #else
-  if (file_access_p (SSDATA (encoded), W_OK | X_OK))
-    return Qt;
-  int err = errno;
-  if (err == EROFS
-      || (err == EACCES && file_access_p (SSDATA (encoded), F_OK)))
-    {
-      errno = err;
-      return Qnil;
-    }
-  return file_test_errno (absname, err);
+  return file_access_p (SSDATA (encoded), W_OK | X_OK) ? Qt : Qnil;
 #endif
 }
 
@@ -2919,7 +2875,8 @@ check_emacs_readlinkat (int fd, Lisp_Object file, char const *encoded_file)
 DEFUN ("file-symlink-p", Ffile_symlink_p, Sfile_symlink_p, 1, 1, 0,
        doc: /* Return non-nil if file FILENAME is the name of a symbolic link.
 The value is the link target, as a string.
-Otherwise it returns nil.
+Return nil if FILENAME does not exist or is not a symbolic link,
+of there was trouble determining whether the file is a symbolic link.
 
 This function does not check whether the link target exists.  */)
   (Lisp_Object filename)
@@ -2935,12 +2892,13 @@ This function does not check whether the link target exists.  */)
   if (!NILP (handler))
     return call2 (handler, Qfile_symlink_p, filename);
 
-  return check_emacs_readlinkat (AT_FDCWD, filename,
-                                 SSDATA (ENCODE_FILE (filename)));
+  return emacs_readlinkat (AT_FDCWD, SSDATA (ENCODE_FILE (filename)));
 }
 
 DEFUN ("file-directory-p", Ffile_directory_p, Sfile_directory_p, 1, 1, 0,
        doc: /* Return t if FILENAME names an existing directory.
+Return nil if FILENAME does not name a directory, or if there
+was trouble determining whether FILENAME is a directory.
 Symbolic links to directories count as directories.
 See `file-symlink-p' to distinguish symlinks.  */)
   (Lisp_Object filename)
@@ -2953,9 +2911,7 @@ See `file-symlink-p' to distinguish symlinks.  */)
   if (!NILP (handler))
     return call2 (handler, Qfile_directory_p, absname);
 
-  if (file_directory_p (absname))
-    return Qt;
-  return file_test_errno (absname, errno);
+  return file_directory_p (absname) ? Qt : Qnil;
 }
 
 /* Return true if FILE is a directory or a symlink to a directory.
@@ -3040,12 +2996,7 @@ really is a readable and searchable directory.  */)
     }
 
   Lisp_Object encoded_absname = ENCODE_FILE (absname);
-  if (file_accessible_directory_p (encoded_absname))
-    return Qt;
-  int err = errno;
-  if (err == EACCES && file_access_p (SSDATA (encoded_absname), F_OK))
-    return Qnil;
-  return file_test_errno (absname, err);
+  return file_accessible_directory_p (encoded_absname) ? Qt : Qnil;
 }
 
 /* If FILE is a searchable directory or a symlink to a
@@ -3108,6 +3059,8 @@ file_accessible_directory_p (Lisp_Object file)
 DEFUN ("file-regular-p", Ffile_regular_p, Sfile_regular_p, 1, 1, 0,
        doc: /* Return t if FILENAME names a regular file.
 This is the sort of file that holds an ordinary stream of data bytes.
+Return nil if FILENAME does not exist or is not a regular file,
+or there was trouble determining whether FILENAME is a regular file.
 Symbolic links to regular files count as regular files.
 See `file-symlink-p' to distinguish symlinks.  */)
   (Lisp_Object filename)
@@ -3133,9 +3086,7 @@ See `file-symlink-p' to distinguish symlinks.  */)
   Vw32_get_true_file_attributes = true_attributes;
 #endif
 
-  if (stat_result == 0)
-    return S_ISREG (st.st_mode) ? Qt : Qnil;
-  return file_test_errno (absname, errno);
+  return stat_result == 0 && S_ISREG (st.st_mode) ? Qt : Qnil;
 }
 
 DEFUN ("file-selinux-context", Ffile_selinux_context,
@@ -3541,20 +3492,15 @@ otherwise, if FILE2 does not exist, the answer is t.  */)
     {
       err1 = errno;
       if (err1 != EOVERFLOW)
-        return file_test_errno (absname1, err1);
+        return file_attribute_errno (absname1, err1);
     }
-
   if (stat (SSDATA (ENCODE_FILE (absname2)), &st2) != 0)
     {
-      file_test_errno (absname2, errno);
+      file_attribute_errno (absname2, errno);
       return Qt;
     }
-
   if (err1)
-    {
-      file_test_errno (absname1, err1);
-      eassume (false);
-    }
+    file_attribute_errno (absname1, err1);
 
   return (timespec_cmp (get_stat_mtime (&st2), get_stat_mtime (&st1)) < 0
           ? Qt : Qnil);
diff --git a/src/lisp.h b/src/lisp.h
index b081ae1cee8..e68d2732e21 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4315,7 +4315,6 @@ extern AVOID report_file_errno (const char *, Lisp_Object, int);
 extern AVOID report_file_error (const char *, Lisp_Object);
 extern AVOID report_file_notify_error (const char *, Lisp_Object);
 extern Lisp_Object file_attribute_errno (Lisp_Object, int);
-extern Lisp_Object file_test_errno (Lisp_Object, int);
 extern bool internal_delete_file (Lisp_Object);
 extern Lisp_Object check_emacs_readlinkat (int, Lisp_Object, char const *);
 extern bool file_directory_p (Lisp_Object);
diff --git a/src/lread.c b/src/lread.c
index 4f3446b09db..151731a81d9 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -1343,26 +1343,18 @@ Return t if the file exists and loads successfully.  */)
           /* openp already checked for newness, no point doing it again.
              FIXME would be nice to get a message when openp
              ignores suffix order due to load_prefer_newer.  */
-          Lisp_Object notfound = found;
           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)
-                    notfound = Fsubstring (found, make_fixnum (0),
-                                           make_fixnum (-1));
                 }
-              if (result != 0)
-                file_test_errno (notfound, err);
-              else if (timespec_cmp (get_stat_mtime (&s1),
-                                     get_stat_mtime (&s2))
-                       < 0)
+
+              if (result == 0
+                  && timespec_cmp (get_stat_mtime (&s1), get_stat_mtime (&s2)) < 0)
                 {
                   /* Make the progress messages mention that source is newer.  */
                   newer = 1;