This isn't perfect as the scripts can still fail if only
certain filters are disabled. This is still an improvement
as now "make check" has better behavior when all encoders
or decoders are disabled.
Grepping ../config.h is simple and fairly clean but it only
works if config.h was created. CMake builds don't create
config.h but they don't use these test scripts either.
Thanks to Sebastian Andrzej Siewior for reporting the problem.
Thanks to Jia Tan for the original patch which grepped xz
error messages instead of config.h.
I suspect that I used these in the original version because
Autoconf's manual describes that such a trick is needed in
some specific situations for portability reasons. None of those
situations listed on Autoconf 2.71 manual apply to these test
scripts though so this cleans them up.
The scripts are now made executable in the build tree.
This way the scripts can be run like programs in
test_scripts.sh. Previously test_scripts.sh always
used sh but it's not correct if @POSIX_SHELL@ is set
to something else by configure.
Thanks to Jonathan Nieder for the patch.
xzdiff was clobbering the exit status from diff in a case
statement used to analyze the exit statuses from "xz" when
its operands were two compressed files. Save and restore
diff's exit status to fix this.
The bug is inherited from zdiff in GNU gzip and was fixed
there on 2009-10-09.
Thanks to Jonathan Nieder for the patch and
to Peter Pallinger for reporting the bug.
