seq: output decimal points consistently with invalid locales

* src/seq.c (print_numbers): Only reset the locale if it
was successfully set originally.
* tests/misc/seq-locale.sh: Add a new test.
* tests/local.mk: Reference the new test.
* NEWS: Mention the fix.

NEWS

@@ -14,6 +14,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   df no longer corrupts displayed multibyte characters on macOS.
   [bug introduced with coreutils-8.18]
 
+  seq no longer outputs inconsistent decimal point characters
+  for the last number, when locales are misconfigured.
+  [bug introduced in coreutils-7.0]
+
   shred, sort, and split no longer falsely report ftruncate errors
   when outputting to less-common file types.  For example, the shell
   command 'sort /dev/null -o /dev/stdout | cat' no longer fails with

src/seq.c

@@ -42,6 +42,9 @@
 
 #define AUTHORS proper_name ("Ulrich Drepper")
 
+/* True if the locale settings were honored.  */
+static bool locale_ok;
+
 /* If true print all number with equal width.  */
 static bool equal_width;
 
@@ -324,9 +327,11 @@ print_numbers (char const *fmt, struct layout layout,
               long double x_val;
               char *x_str;
               int x_strlen;
-              setlocale (LC_NUMERIC, "C");
+              if (locale_ok)
+                setlocale (LC_NUMERIC, "C");
               x_strlen = asprintf (&x_str, fmt, x);
-              setlocale (LC_NUMERIC, "");
+              if (locale_ok)
+                setlocale (LC_NUMERIC, "");
               if (x_strlen < 0)
                 xalloc_die ();
               x_str[x_strlen - layout.suffix_len] = '\0';
@@ -559,7 +564,7 @@ main (int argc, char **argv)
 
   initialize_main (&argc, &argv);
   set_program_name (argv[0]);
-  setlocale (LC_ALL, "");
+  locale_ok = !!setlocale (LC_ALL, "");
   bindtextdomain (PACKAGE, LOCALEDIR);
   textdomain (PACKAGE);
 

tests/local.mk

@@ -244,6 +244,7 @@ all_tests =					\
   tests/misc/seq.pl				\
   tests/misc/seq-epipe.sh			\
   tests/misc/seq-io-errors.sh			\
+  tests/misc/seq-locale.sh			\
   tests/misc/seq-long-double.sh			\
   tests/misc/seq-precision.sh			\
   tests/misc/head.pl				\

tests/misc/seq-locale.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+# Test for output with appropriate precision
+
+# Copyright (C) 2019 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ seq
+
+# With coreutils-8.30 and earlier, the last decimal point would be ','
+# when setlocale(LC_ALL, "") failed, but setlocale(LC_NUMERIC, "") succeeded.
+LC_ALL= LANG=invalid LC_NUMERIC=$LOCALE_FR_UTF8 seq 0.1 0.2 0.7 > out || fail=1
+uniq -w2 out > out-merge || framework_failure_
+test "$(wc -l < out-merge)" = 1 || { fail=1; cat out; }
+
+Exit $fail