Do not treat ~nosuchuser as an absolute file name

Derived from Ken Brown’s patch (Bug#36502#97).
* doc/lispref/files.texi (Relative File Names):
* etc/NEWS: Document this.
* src/fileio.c (user_homedir): New function.
(Fexpand_file_name, file_name_absolute_p): Use it.
(search_embedded_absfilename): Simplify via file_name_absolute_p.
* test/src/fileio-tests.el (fileio-tests--no-such-user): New test.

1 files changed, 55 insertions, 66 deletions

diff --git a/src/fileio.c b/src/fileio.c
index e4269b96a37..d1a7f39ac95 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -744,6 +744,31 @@ file_name_absolute_no_tilde_p (Lisp_Object name)
   return IS_ABSOLUTE_FILE_NAME (SSDATA (name));
 }
 
+/* Return the home directory of the user NAME, or a null pointer if
+   NAME is empty or the user does not exist or the user's home
+   directory is not an absolute file name.  NAME is an array of bytes
+   that continues up to (but not including) the next NUL byte or
+   directory separator.  The returned string lives in storage good
+   until the next call to this or similar functions.  */
+static char *
+user_homedir (char const *name)
+{
+  ptrdiff_t length;
+  for (length = 0; name[length] && !IS_DIRECTORY_SEP (name[length]); length++)
+    continue;
+  if (length == 0)
+    return NULL;
+  USE_SAFE_ALLOCA;
+  char *p = SAFE_ALLOCA (length + 1);
+  memcpy (p, name, length);
+  p[length] = 0;
+  struct passwd *pw = getpwnam (p);
+  SAFE_FREE ();
+  if (!pw || (pw->pw_dir && !IS_ABSOLUTE_FILE_NAME (pw->pw_dir)))
+    return NULL;
+  return pw->pw_dir;
+}
+
 DEFUN ("expand-file-name", Fexpand_file_name, Sexpand_file_name, 1, 2, 0,
        doc: /* Convert filename NAME to absolute, and canonicalize it.
 Second arg DEFAULT-DIRECTORY is directory to start with if NAME is relative
@@ -788,7 +813,6 @@ the root directory.  */)
   char *target;
 
   ptrdiff_t tlen;
-  struct passwd *pw;
 #ifdef DOS_NT
   int drive = 0;
   bool collapse_newdir = true;
@@ -1153,39 +1177,29 @@ the root directory.  */)
         }
       else                      /* ~user/filename */
         {
-          char *o, *p;
-          for (p = nm; *p && !IS_DIRECTORY_SEP (*p); p++)
-            continue;
-          o = SAFE_ALLOCA (p - nm + 1);
-          memcpy (o, nm, p - nm);
-          o[p - nm] = 0;
-
-          block_input ();
-          pw = getpwnam (o + 1);
-          unblock_input ();
-          if (pw)
+          char *nmhome = user_homedir (nm + 1);
+          if (nmhome)
             {
-              Lisp_Object tem;
-
-              newdir = pw->pw_dir;
-              /* `getpwnam' may return a unibyte string, which will
-                 bite us when we expect the directory to be multibyte.  */
-              tem = make_unibyte_string (newdir, strlen (newdir));
-              newdirlim = newdir + SBYTES (tem);
-              if (multibyte && !STRING_MULTIBYTE (tem))
+              ptrdiff_t nmhomelen = strlen (nmhome);
+              newdir = nmhome;
+              newdirlim = newdir + nmhomelen;
+              if (multibyte)
                 {
-                  hdir = DECODE_FILE (tem);
+                  AUTO_STRING_WITH_LEN (lisp_nmhome, nmhome, nmhomelen);
+                  hdir = DECODE_FILE (lisp_nmhome);
                   newdir = SSDATA (hdir);
                   newdirlim = newdir + SBYTES (hdir);
                 }
-              nm = p;
+
+              while (*++nm && !IS_DIRECTORY_SEP (*nm))
+                continue;
 #ifdef DOS_NT
               collapse_newdir = false;
 #endif
             }
 
           /* If we don't find a user of that name, leave the name
-             unchanged; don't move nm forward to p.  */
+             unchanged.  */
         }
     }
 
@@ -1667,18 +1681,6 @@ See also the function `substitute-in-file-name'.")
 }
 #endif
 
-bool
-file_name_absolute_p (const char *filename)
-{
-  return
-    (IS_DIRECTORY_SEP (*filename) || *filename == '~'
-#ifdef DOS_NT
-     || (IS_DRIVE (*filename) && IS_DEVICE_SEP (filename[1])
-         && IS_DIRECTORY_SEP (filename[2]))
-#endif
-     );
-}
-
 /* Put into BUF the concatenation of DIR and FILE, with an intervening
    directory separator if needed.  Return a pointer to the NUL byte
    at the end of the concatenated string.  */
@@ -1774,7 +1776,10 @@ get_homedir (void)
   return ahome;
 }
 
-/* If /~ or // appears, discard everything through first slash.  */
+/* If a directory separator followed by an absolute file name (e.g.,
+   "//foo", "/~", "/~someuser") appears in NM, return the address of
+   the absolute file name.  Otherwise return NULL.  ENDP is the
+   address of the null byte at the end of NM.  */
 static char *
 search_embedded_absfilename (char *nm, char *endp)
 {
@@ -1784,34 +1789,8 @@ search_embedded_absfilename (char *nm, char *endp)
         && !IS_DIRECTORY_SEP (p[1]));
 #endif
   for (; p < endp; p++)
-    {
-      if (IS_DIRECTORY_SEP (p[-1]) && file_name_absolute_p (p))
-        {
-          char *s;
-          for (s = p; *s && !IS_DIRECTORY_SEP (*s); s++)
-            continue;
-          if (p[0] == '~' && s > p + 1) /* We've got "/~something/".  */
-            {
-              USE_SAFE_ALLOCA;
-              char *o = SAFE_ALLOCA (s - p + 1);
-              struct passwd *pw;
-              memcpy (o, p, s - p);
-              o [s - p] = 0;
-
-              /* If we have ~user and `user' exists, discard
-                 everything up to ~.  But if `user' does not exist, leave
-                 ~user alone, it might be a literal file name.  */
-              block_input ();
-              pw = getpwnam (o + 1);
-              unblock_input ();
-              SAFE_FREE ();
-              if (pw)
-                return p;
-            }
-          else
-            return p;
-        }
-    }
+    if (IS_DIRECTORY_SEP (p[-1]) && file_name_absolute_p (p))
+      return p;
   return NULL;
 }
 
@@ -2696,13 +2675,23 @@ This happens for interactive use with M-x.  */)
 
 DEFUN ("file-name-absolute-p", Ffile_name_absolute_p, Sfile_name_absolute_p,
        1, 1, 0,
-       doc: /* Return t if FILENAME is an absolute file name or starts with `~'.
-On Unix, absolute file names start with `/'.  */)
+       doc: /* Return t if FILENAME is an absolute file name.
+On Unix, absolute file names start with `/'.  In Emacs, an absolute
+file name can also start with an initial `~' or `~USER' component,
+where USER is a valid login name.  */)
   (Lisp_Object filename)
 {
   CHECK_STRING (filename);
   return file_name_absolute_p (SSDATA (filename)) ? Qt : Qnil;
 }
+
+bool
+file_name_absolute_p (char const *filename)
+{
+  return (IS_ABSOLUTE_FILE_NAME (filename)
+          || (filename[0] == '~'
+              && (!filename[1] || user_homedir (&filename[1]))));
+}
 
 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).