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M4's output pipe was not being drained upon fatal errors during scan_skel. As a result, broken-pipe messages from M4 were seen on at least AIX, HP-UX, Solaris, and RHEL4, and this caused a failure in the test suite. The problem was that, on platforms where the default disposition for SIGPIPE is ignore instead of terminate, M4 sometimes saw fwrite fail with errno=EPIPE and then reported it. However, there's some sort of race condition, because the new test group occasionally succeeded. Reported by Albert Chin at <http://lists.gnu.org/archive/html/bug-bison/2010-02/msg00004.html>. There were also problems with the test suite livelocking on Tru64 5.1b. Reported by Didier Godefroy at <http://lists.gnu.org/archive/html/bug-bison/2009-05/msg00005.html>. Switching to create_pipe_bidi suggested by Akim Demaille. To attempt to solve both of these problems, switch to gnulib's create_pipe_bidi and register M4 process as a slave. Along the way, clean up file name conflict handling, which was affected by the broken-pipe problem before the switch. * NEWS (2.4.2): Document. * THANKS (Didier Godefroy): Add. * bootstrap.conf (gnulib_modules): Add pipe. * gnulib: Update to latest to make sure we have all the latest fixes. * lib/Makefile.am (libbison_a_SOURCES): Remove subpipe.h and subpipe.c. * po/POTFILES.in (lib/subpipe.c): Remove. * src/files.c (compute_output_file_names): Update invocations of output_file_name_check. (output_file_name_check): In the case that the grammar file would be overwritten, use complain instead of fatal, but replace the output file name with /dev/null. Use the /dev/null solution for the case of two conflicting output files as well because it seems safer in case Bison one day tries to open both files at the same time. * src/files.h (output_file_name_check): Update prototype. * src/output.c (output_skeleton): Use create_pipe_bidi and wait_subprocess. Assert that scan_skel completely drains the pipe. * src/scan-skel.l (at_directive_perform): Update output_file_name_check invocation. * tests/output.at (AT_CHECK_CONFLICTING_OUTPUT): Check that the grammar file actually isn't overwritten. (Conflicting output files: -o foo.y): Update expected output. * tests/skeletons.at (Fatal errors but M4 continues producing output): New test group.