tar: --owner and --group names and numbers

The --owner and --group options now accept operands of the form
NAME:NUM, so that you can specify both symbolic name and numeric
ID for owner and group.  Also, in these options, NAME no longer
needs to be present in the current host's user and group
databases; this implements Debian enhancement request 136231
<http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=136231> reported
by Mark W. Eichin, communicated by Thayne Harbaugh to bug-tar in
<http://lists.gnu.org/archive/html/bug-tar/2011-08/msg00001.html>.
* NEWS, doc/tar.texi (Option Summary, override): Document enhancement.
* src/common.h (group_name_option, owner_name_option): New decls.
* src/create.c (start_header): Don't assume owner and group names
are in current host database.
* src/tar.c (parse_owner_group): New function, for parsing NAME:NUM.
(parse_opt): Use it.
(decode_options): Initialize owner_name_option, group_name_option.
* tests/owner.at: New file, to test this enhancement.
* tests/Makefile.am (TESTSUITE_AT): Add it.
* tests/testsuite.at: Include it.

doc/tar.texi

@@ -2713,9 +2713,9 @@ tutorial}).
 @item --group=@var{group}
 
 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
-rather than the group from the source file.  @var{group} is first decoded
-as a group symbolic name, but if this interpretation fails, it has to be
-a decimal numeric group @acronym{ID}.  @xref{override}.
+rather than the group from the source file.  @var{group} can specify a
+symbolic name, or a numeric @acronym{ID}, or both as
+@var{name}:@var{id}.  @xref{override}.
 
 Also see the comments for the @option{--owner=@var{user}} option.
 
@@ -3082,8 +3082,8 @@ from an archive.  @xref{Overwrite Old Files}.
 
 Specifies that @command{tar} should use @var{user} as the owner of members
 when creating archives, instead of the user associated with the source
-file.  @var{user} is first decoded as a user symbolic name, but if
-this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
+file.  @var{user} can specify a symbolic name, or a numeric
+@acronym{ID}, or both as @var{name}:@var{id}.
 @xref{override}.
 
 This option does not affect extraction from archives.
@@ -4947,8 +4947,22 @@ tar: Option --mtime: Treating date `yesterday' as 2006-06-20
 
 Specifies that @command{tar} should use @var{user} as the owner of members
 when creating archives, instead of the user associated with the source
-file.  The argument @var{user} can be either an existing user symbolic
-name, or a decimal numeric user @acronym{ID}.
+file.
+
+If @var{user} contains a colon, it is taken to be of the form
+@var{name}:@var{id} where a nonempty @var{name} specifies the user
+name and a nonempty @var{id} specifies the decimal numeric user
+@acronym{ID}.  If @var{user} does not contain a colon, it is taken to
+be a user number if it is one or more decimal digits; otherwise it is
+taken to be a user name.
+
+If a name is given but no number, the number is inferred from the
+current host's user database if possible, and the file's user number
+is used otherwise.  If a number is given but no name, the name is
+inferred from the number if possible, and an empty name is used
+otherwise.  If both name and number are given, the user database is
+not consulted, and the name and number need not be valid on the
+current host.
 
 There is no value indicating a missing number, and @samp{0} usually means
 @code{root}.  Some people like to force @samp{0} as the value to offer in
@@ -4971,8 +4985,9 @@ $ @kbd{tar -c -f archive.tar --owner=root .}
 @opindex group
 
 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
-rather than the group from the source file.  The argument @var{group}
-can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
+rather than the group from the source file.  As with @option{--owner},
+the argument @var{group} can be an existing group symbolic name, or a
+decimal numeric group @acronym{ID}, or @var{name}:@var{id}.
 @end table
 
 @node Ignore Failed Read