seq: fix superfluous output line

Under certain circumstances seq prints an extra line when the output
format has custom format with characters following the printed numbers:

    $ seq -f "%g " 1000000 1000000
     1e+06
     1e+06

This is due to the "print_extra_number" logic using strings to determine
whether a 'extra number' is needed, but only one string was trimmed
when using a custom printf format.

Prompted by https://lists.gnu.org/r/coreutils/2019-08/msg00001.html

* NEWS: Mention fix.
* src/seq.c (print_numbers): Trim the 'x0_str' string before comparing
it to the previous 'x_str' string.
* tests/misc/seq-extra-number.sh: Add this scenario.
* tests/local.mk (all_tests): Add new test.

NEWS

@@ -34,6 +34,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   for --numeric, --hex, or default alphabetic suffixes respectively.
   [bug introduced in coreutils-8.24]
 
+  seq no longer prints an extra line under certain circumstances (such as
+  'seq -f "%g " 1000000 1000000').
+  [bug introduced in coreutils-6.10]
+
 ** New Features
 
   od --skip-bytes now can use lseek even if the input is not a regular

src/seq.c

@@ -340,8 +340,10 @@ print_numbers (char const *fmt, struct layout layout,
                   && x_val == last)
                 {
                   char *x0_str = NULL;
-                  if (asprintf (&x0_str, fmt, x0) < 0)
+                  int x0_strlen = asprintf (&x0_str, fmt, x0);
+                  if (x0_strlen < 0)
                     xalloc_die ();
+                  x0_str[x0_strlen - layout.suffix_len] = '\0';
                   print_extra_number = !STREQ (x0_str, x_str);
                   free (x0_str);
                 }

tests/local.mk

@@ -245,6 +245,7 @@ all_tests =					\
   tests/misc/test.pl				\
   tests/misc/seq.pl				\
   tests/misc/seq-epipe.sh			\
+  tests/misc/seq-extra-number.sh		\
   tests/misc/seq-io-errors.sh			\
   tests/misc/seq-locale.sh			\
   tests/misc/seq-long-double.sh			\

tests/misc/seq-extra-number.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+# Test the "print_extra_number" logic seq.c:print_numbers()
+
+# 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
+
+##
+## Test 1: the documented reason for the logic
+##
+cat<<'EOF'>exp1 || framework_failure_
+0.000000
+0.000001
+0.000002
+0.000003
+EOF
+
+seq 0 0.000001 0.000003 > out1 || fail=1
+compare exp1 out1 || fail=1
+
+
+##
+## Test 2: before 8.32, this resulted in TWO lines
+## (print_extra_number was erroneously set to true)
+## The '=' is there instead of a space to ease visual inspection.
+cat<<'EOF'>exp2 || framework_failure_
+1e+06=
+EOF
+
+seq -f "%g=" 1000000 1000000 > out2 || fail=1
+compare exp2 out2 || fail=1
+
+Exit $fail