all: be less strict about usage if POSIX 2008

sort, tail, and uniq now support traditional usage like 'sort +2'
and 'tail +10' on systems conforming to POSIX 1003.1-2008 and later.
* NEWS: Document this.
* doc/coreutils.texi (Standards conformance, tail invocation)
(sort invocation, uniq invocation, touch invocation):
Document new behavior, or behavior's dependence on POSIX 1003.1-2001.
* src/sort.c (struct keyfield.traditional_used):
Rename from obsolete_used, since implementations are now allowed
to support it.  All uses changed.
(main): Allow traditional usage if _POSIX2_VERSION is 200809.
* src/tail.c (parse_obsolete_option): Distinguish between
traditional usage (which POSIX 2008 and later allows) and obsolete
(which it still does not).
* src/uniq.c (strict_posix2): New function.
(main): Allow traditional usage if _POSIX2_VERSION is 200809.
* tests/misc/tail.pl: Test for new behavior.

6 files changed, 64 insertions, 40 deletions

diff --git a/NEWS b/NEWS
index 3b2e461be..ae42581cb 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,13 @@ GNU coreutils NEWS                                    -*- outline -*-
    stty --help no longer outputs extraneous gettext header lines
    for translated languages. [bug introduced in coreutils-8.24]
 
+** Changes in behavior
+
+   sort, tail, and uniq now support traditional usage like 'sort +2'
+   and 'tail +10' on systems conforming to POSIX 1003.1-2008 and later.
+   The 2008 edition of POSIX dropped the requirement that arguments
+   like '+2' must be treated as file names.
+
 
 * Noteworthy changes in release 8.25 (2016-01-20) [stable]
 
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index a07e46ef1..45706bdbf 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -1506,10 +1506,11 @@ probably do not need to define @env{POSIXLY_CORRECT}.
 Newer versions of POSIX are occasionally incompatible with older
 versions.  For example, older versions of POSIX required the
 command @samp{sort +1} to sort based on the second and succeeding
-fields in each input line, but starting with POSIX 1003.1-2001
+fields in each input line, but in POSIX 1003.1-2001
 the same command is required to sort the file named @file{+1}, and you
 must instead use the command @samp{sort -k 2} to get the field-based
-sort.
+sort.  To complicate things further, POSIX 1003.1-2008 allows an
+implementation to have either the old or the new behavior.
 
 @vindex _POSIX2_VERSION
 The GNU utilities normally conform to the version of POSIX
@@ -1520,10 +1521,10 @@ the year and month the standard was adopted.  Three values are currently
 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
 POSIX 1003.2-1992, @samp{200112} stands for POSIX
 1003.1-2001, and @samp{200809} stands for POSIX 1003.1-2008.
-For example, if you have a newer system but are running software
-that assumes an older version of POSIX and uses @samp{sort +1}
-or @samp{tail +10}, you can work around any compatibility problems by setting
-@samp{_POSIX2_VERSION=199209} in your environment.
+For example, if you have a POSIX 1003.1-2001 system but are running software
+containing traditional usage like @samp{sort +1} or @samp{tail +10},
+you can work around the compatibility problems by setting
+@samp{_POSIX2_VERSION=200809} in your environment.
 
 @c This node is named "Multi-call invocation", not the usual
 @c "coreutils invocation", so that shell commands like
@@ -3060,17 +3061,18 @@ by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
 which has the same meaning as @option{-f}.
 
 @vindex _POSIX2_VERSION
-On older systems, the leading @samp{-} can be replaced by @samp{+} in
-the obsolete option syntax with the same meaning as in counts, and
-obsolete usage overrides normal usage when the two conflict.
-This obsolete behavior can be enabled or disabled with the
+On systems not conforming to POSIX 1003.1-2001, the leading @samp{-}
+can be replaced by @samp{+} in the traditional option syntax with the
+same meaning as in counts, and on obsolete systems predating POSIX
+1003.1-2001 traditional usage overrides normal usage when the two
+conflict.  This behavior can be controlled with the
 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
 conformance}).
 
-Scripts intended for use on standard hosts should avoid obsolete
+Scripts intended for use on standard hosts should avoid traditional
 syntax and should use @option{-c @var{num}[b]}, @option{-n
 @var{num}}, and/or @option{-f} instead.  If your script must also
-run on hosts that support only the obsolete syntax, you can often
+run on hosts that support only the traditional syntax, you can often
 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
 '$p'} rather than @samp{tail -1}.  If that's not possible, the script
 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
@@ -4536,23 +4538,24 @@ is counted from the first nonblank character of the field.
 
 @vindex _POSIX2_VERSION
 @vindex POSIXLY_CORRECT
-On older systems, @command{sort} supports an obsolete origin-zero
+On systems not conforming to POSIX 1003.1-2001,
+@command{sort} supports a traditional origin-zero
 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
-The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
+The traditional command @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
 
-This obsolete behavior can be enabled or disabled with the
+This traditional behavior can be controlled with the
 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
-not set by using the obsolete syntax with @samp{-@var{pos2}} present.
+not set by using the traditional syntax with @samp{-@var{pos2}} present.
 
-Scripts intended for use on standard hosts should avoid obsolete
+Scripts intended for use on standard hosts should avoid traditional
 syntax and should use @option{-k} instead.  For example, avoid
 @samp{sort +2}, since it might be interpreted as either @samp{sort
 ./+2} or @samp{sort -k 3}.  If your script must also run on hosts that
-support only the obsolete syntax, it can use a test like @samp{if sort
+support only the traditional syntax, it can use a test like @samp{if sort
 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
 to use.
 
@@ -4911,7 +4914,7 @@ a null string for comparison if a line has fewer than @var{n} fields.  Fields
 are sequences of non-space non-tab characters that are separated from
 each other by at least one space or tab.
 
-For compatibility @command{uniq} supports an obsolete option syntax
+For compatibility @command{uniq} supports a traditional option syntax
 @option{-@var{n}}.  New scripts should use @option{-f @var{n}} instead.
 
 @item -s @var{n}
@@ -4923,11 +4926,12 @@ for comparison if a line has fewer than @var{n} characters.  If you use both
 the field and character skipping options, fields are skipped over first.
 
 @vindex _POSIX2_VERSION
-On older systems, @command{uniq} supports an obsolete option syntax
+On systems not conforming to POSIX 1003.1-2001,
+@command{uniq} supports a traditional option syntax
 @option{+@var{n}}.
-This obsolete behavior can be enabled or disabled with the
+Although this traditional behavior can be controlled with the
 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
-conformance}), but portable scripts should avoid commands whose
+conformance}), portable scripts should avoid commands whose
 behavior depends on this variable.
 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
 the ambiguous @samp{uniq +10}.
@@ -10981,7 +10985,8 @@ On the atypical systems that support leap seconds, @var{ss} may be
 @end table
 
 @vindex _POSIX2_VERSION
-On older systems, @command{touch} supports an obsolete syntax, as follows.
+On systems predating POSIX 1003.1-2001,
+@command{touch} supports an obsolete syntax, as follows.
 If no timestamp is given with any of the @option{-d}, @option{-r}, or
 @option{-t} options, and if there are two or more @var{file}s and the
 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
@@ -10989,9 +10994,9 @@ would be a valid argument to the @option{-t} option (if the @var{yy}, if
 any, were moved to the front), and if the represented year
 is in the range 1969--1999, that argument is interpreted as the time
 for the other files instead of as a file name.
-This obsolete behavior can be enabled or disabled with the
+Although this obsolete behavior can be controlled with the
 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
-conformance}), but portable scripts should avoid commands whose
+conformance}), portable scripts should avoid commands whose
 behavior depends on this variable.
 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
diff --git a/src/sort.c b/src/sort.c
index 62acb6298..aa52b7569 100644
--- a/src/sort.c
+++ b/src/sort.c
@@ -224,7 +224,7 @@ struct keyfield
   bool month;			/* Flag for comparison by month name. */
   bool reverse;			/* Reverse the sense of comparison. */
   bool version;			/* sort by version number */
-  bool obsolete_used;		/* obsolescent key option format is used. */
+  bool traditional_used;	/* Traditional key option format is used. */
   struct keyfield *next;	/* Next keyfield to try. */
 };
 
@@ -2394,7 +2394,7 @@ key_warnings (struct keyfield const *gkey, bool gkey_only)
 
   for (key = keylist; key; key = key->next, keynum++)
     {
-      if (key->obsolete_used)
+      if (key->traditional_used)
         {
           size_t sword = key->sword;
           size_t eword = key->eword;
@@ -4183,7 +4183,8 @@ main (int argc, char **argv)
   size_t nthreads = 0;
   size_t nfiles = 0;
   bool posixly_correct = (getenv ("POSIXLY_CORRECT") != NULL);
-  bool obsolete_usage = (posix2_version () < 200112);
+  int posix_ver = posix2_version ();
+  bool traditional_usage = ! (200112 <= posix_ver && posix_ver < 200809);
   char **files;
   char *files_from = NULL;
   struct Tokens tok;
@@ -4288,13 +4289,13 @@ main (int argc, char **argv)
     {
       /* Parse an operand as a file after "--" was seen; or if
          pedantic and a file was seen, unless the POSIX version
-         predates 1003.1-2001 and -c was not seen and the operand is
+         is not 1003.1-2001 and -c was not seen and the operand is
          "-o FILE" or "-oFILE".  */
       int oi = -1;
 
       if (c == -1
           || (posixly_correct && nfiles != 0
-              && ! (obsolete_usage
+              && ! (traditional_usage
                     && ! checkonly
                     && optind != argc
                     && argv[optind][0] == '-' && argv[optind][1] == 'o'
@@ -4315,8 +4316,8 @@ main (int argc, char **argv)
             {
               bool minus_pos_usage = (optind != argc && argv[optind][0] == '-'
                                       && ISDIGIT (argv[optind][1]));
-              obsolete_usage |= minus_pos_usage && !posixly_correct;
-              if (obsolete_usage)
+              traditional_usage |= minus_pos_usage && !posixly_correct;
+              if (traditional_usage)
                 {
                   /* Treat +POS1 [-POS2] as a key if possible; but silently
                      treat an operand as a file if it is not a valid +POS1.  */
@@ -4356,7 +4357,7 @@ main (int argc, char **argv)
                             badfieldspec (optarg1,
                                       N_("stray character in field spec"));
                         }
-                      key->obsolete_used = true;
+                      key->traditional_used = true;
                       insertkey (key);
                     }
                 }
diff --git a/src/tail.c b/src/tail.c
index 2a72a93f0..caa54076a 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1981,7 +1981,6 @@ parse_obsolete_option (int argc, char * const *argv, uintmax_t *n_units)
   const char *p;
   const char *n_string;
   const char *n_string_end;
-  bool obsolete_usage;
   int default_count = DEFAULT_N_LINES;
   bool t_from_start;
   bool t_count_lines = true;
@@ -1994,7 +1993,9 @@ parse_obsolete_option (int argc, char * const *argv, uintmax_t *n_units)
          || (3 <= argc && argc <= 4 && STREQ (argv[2], "--"))))
     return false;
 
-  obsolete_usage = (posix2_version () < 200112);
+  int posix_ver = posix2_version ();
+  bool obsolete_usage = posix_ver < 200112;
+  bool traditional_usage = obsolete_usage || 200809 <= posix_ver;
   p = argv[1];
 
   switch (*p++)
@@ -2003,8 +2004,8 @@ parse_obsolete_option (int argc, char * const *argv, uintmax_t *n_units)
       return false;
 
     case '+':
-      /* Leading "+" is a file name in the non-obsolete form.  */
-      if (!obsolete_usage)
+      /* Leading "+" is a file name in the standard form.  */
+      if (!traditional_usage)
         return false;
 
       t_from_start = true;
@@ -2014,7 +2015,7 @@ parse_obsolete_option (int argc, char * const *argv, uintmax_t *n_units)
       /* In the non-obsolete form, "-" is standard input and "-c"
          requires an option-argument.  The obsolete multidigit options
          are supported as a GNU extension even when conforming to
-         POSIX 1003.1-2001, so don't complain about them.  */
+         POSIX 1003.1-2001 or later, so don't complain about them.  */
       if (!obsolete_usage && !p[p[0] == 'c'])
         return false;
 
diff --git a/src/uniq.c b/src/uniq.c
index 0e118da9d..896ce938f 100644
--- a/src/uniq.c
+++ b/src/uniq.c
@@ -226,6 +226,13 @@ Also, comparisons honor the rules specified by 'LC_COLLATE'.\n\
   exit (status);
 }
 
+static bool
+strict_posix2 (void)
+{
+  int posix_ver = posix2_version ();
+  return 200112 <= posix_ver && posix_ver < 200809;
+}
+
 /* Convert OPT to size_t, reporting an error using MSGID if OPT is
    invalid.  Silently convert too-large values to SIZE_MAX.  */
 
@@ -533,7 +540,7 @@ main (int argc, char **argv)
           {
             unsigned long int size;
             if (optarg[0] == '+'
-                && posix2_version () < 200112
+                && ! strict_posix2 ()
                 && xstrtoul (optarg, NULL, 10, &size, "") == LONGINT_OK
                 && size <= SIZE_MAX)
               skip_chars = size;
diff --git a/tests/misc/tail.pl b/tests/misc/tail.pl
index 0d9bc4834..57ed62db5 100755
--- a/tests/misc/tail.pl
+++ b/tests/misc/tail.pl
@@ -116,12 +116,15 @@ foreach my $t (@tv)
     $ret
       and push @$e, {EXIT=>$ret}, {ERR=>$err_msg}, {ERR_SUBST=>$err_sub};
 
-    $test_name =~ /^(obs-plus-|minus-)/
+    $test_name =~ /^minus-/
       and push @$e, {ENV=>'_POSIX2_VERSION=199209'};
 
     $test_name =~ /^(err-6|c-2)$/
       and push @$e, {ENV=>'_POSIX2_VERSION=200112'};
 
+    $test_name =~ /^obs-plus-/
+      and push @$e, {ENV=>'_POSIX2_VERSION=200809'};
+
     $test_name =~ /^f-pipe-/
       and push @$e, {ENV=>'POSIXLY_CORRECT=1'};