[Emacs-diffs] master a5063aa: Do not treat ~nosuchuser as an absolute file name

[Paul Eggert]

branch: master
commit a5063aa8b174db286a0e83b8ffdd4e65c521f733
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>

    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.
---
 doc/lispref/files.texi   |  10 +++-
 etc/NEWS                 |   3 ++
 src/fileio.c             | 121 +++++++++++++++++++++--------------------------
 test/src/fileio-tests.el |  11 +++++
 4 files changed, 78 insertions(+), 67 deletions(-)

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 0519f78..0ea8a4f 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -2154,7 +2154,11 @@ backslash, or with a drive specification 
@samp{@var{x}:/}, where
 
 @defun file-name-absolute-p filename
 This function returns @code{t} if file @var{filename} is an absolute
-file name or begins with @samp{~}, @code{nil} otherwise.
+file name, @code{nil} otherwise.  A file name is considered to be
+absolute if its first component is @samp{~}, or is @samp{~@var{user}}
+where @var{user} is a valid login name.  In the following examples,
+assume that there is a user named @samp{rms} but no user named
+@samp{nosuchuser}.
 
 @example
 @group
@@ -2162,6 +2166,10 @@ file name or begins with @samp{~}, @code{nil} otherwise.
      @result{} t
 @end group
 @group
+(file-name-absolute-p "~nosuchuser/foo")
+     @result{} nil
+@end group
+@group
 (file-name-absolute-p "rms/foo")
      @result{} nil
 @end group
diff --git a/etc/NEWS b/etc/NEWS
index 5313270..08f0e65 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1815,6 +1815,9 @@ relative to the 'default-directory' of the current 
buffer.  We recommend
 always setting "$HOME" to an absolute file name, so that its meaning is
 independent of where Emacs was started.
 
+** file-name-absolute-p no longer considers "~foo" to be an absolute
+file name if there is no user named "foo".
+
 ** The FILENAME argument to 'file-name-base' is now mandatory and no
 longer defaults to 'buffer-file-name'.
 
diff --git a/src/fileio.c b/src/fileio.c
index e4269b9..d1a7f39 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).
diff --git a/test/src/fileio-tests.el b/test/src/fileio-tests.el
index 813ee5f..09a5b14 100644
--- a/test/src/fileio-tests.el
+++ b/test/src/fileio-tests.el
@@ -136,3 +136,14 @@ Also check that an encoding error can appear in a symlink."
          (name (expand-file-name "bar")))
     (should (and (file-name-absolute-p name)
                  (not (eq (aref name 0) ?~))))))
+
+(ert-deftest fileio-tests--no-such-user ()
+  "Test file-name-absolute-p on ~nosuchuser."
+  (unless (user-full-name "nosuchuser")
+    (should (not (file-name-absolute-p "~nosuchuser")))
+    (should (not (file-name-absolute-p "~nosuchuser/")))
+    (should (not (file-name-absolute-p "~nosuchuser//")))
+    (should (not (file-name-absolute-p "~nosuchuser/foo")))
+    (should (not (file-name-absolute-p "~nosuchuser/foo/")))
+    (should (not (file-name-absolute-p "~nosuchuser/foo//")))
+    (should (not (file-name-absolute-p "~nosuchuser/foo/bar")))))