mktmpdir: Ensure that $tmp is always an absolute pathname.

Several autotools programs use ‘do’ to evaluate Perl code
generated into a file in the temporary directory created by
Autom4te::General::mktmpdir.  If the environment variable
TMPDIR is a relative path, mktmpdir will set $tmp to a
relative path and we’ll end up trying to ‘do’ a relative
path, which searches for the file in @INC.  This doesn’t
work under perl 5.26 or later, because ‘.’ was removed
from @INC in that version (for security reasons).

Ensure that mktmpdir sets $tmp to an absolute pathname.
Also use File::Temp::tempdir to create the temporary
directory, instead of shelling out to ‘mktemp -d’;
this eliminates a subprocess and means we don’t have
to worry about cleaning up the directory on exit.

Problem found by Kent Fredric and reported as
<https://bugs.gentoo.org/625576>.
Supersedes Gentoo’s autoconf-2.69-perl-5.26-2.patch.

* lib/Autom4te/General.pm
  (mktmpdir): Use File::Temp to create temporary directory.
  Ensure that $tmp is an absolute path.
  (END): No need to clean up $tmp.

* tests/tools.at (autotools and relative TMPDIR): New test.

1 files changed, 32 insertions, 0 deletions

diff --git a/tests/tools.at b/tests/tools.at
index 2ad46ca1..6288de00 100644
--- a/tests/tools.at
+++ b/tests/tools.at
@@ -1621,3 +1621,35 @@ END
 done
 
 AT_CLEANUP
+
+# autotools and file names containing whitespace
+# ----------------------------------------------
+
+AT_SETUP([autotools and relative TMPDIR])
+
+# We use aclocal.
+AT_CHECK([aclocal --version || exit 77], [], [ignore], [ignore])
+
+mkdir _tmp
+TMPDIR=_tmp
+export TMPDIR
+
+AT_DATA([configure.ac],
+[[AC_INIT(x,0)
+AC_CONFIG_HEADERS([config.h:config.hin])
+AC_MACRO
+AC_OUTPUT
+]])
+
+mkdir m4
+AT_DATA([m4/foo.m4],
+[[AC_DEFUN([AC_MACRO],
+[AC_DEFINE([HAVE_MACROS], 1, [Define if you have macros.])])
+]])
+
+AT_CHECK([aclocal -I m4])
+AT_CHECK_AUTOHEADER([], [HAVE_MACROS])
+AT_CHECK_AUTOCONF
+AT_CHECK_CONFIGURE
+
+AT_CLEANUP