portability: fix several issues with M4 subprocess.

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/local.mk (lib_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.
(cherry picked from commit 22cc8d813ee57c9631e527a31010ab138f9b7e06)

Conflicts:

	NEWS
	bootstrap.conf
	lib/.cvsignore
	lib/.gitignore
	lib/Makefile.am
	m4/.cvsignore
	m4/.gitignore
	src/output.c

2 files changed, 45 insertions, 1 deletions

diff --git a/tests/output.at b/tests/output.at
index 94c618d8..bb6d4491 100644
--- a/tests/output.at
+++ b/tests/output.at
@@ -145,7 +145,9 @@ AT_DATA([$1],
 foo: {};
 ]])
 
+[cp ]$1[ expout]
 AT_BISON_CHECK([$3 $1], $5, [], [$4])
+AT_CHECK([[cat $1]], [[0]], [expout])
 AT_CLEANUP
 ])
 
@@ -165,7 +167,7 @@ AT_CHECK_CONFLICTING_OUTPUT([foo.y],
 ])
 
 AT_CHECK_CONFLICTING_OUTPUT([foo.y], [], [-o foo.y],
-[foo.y: fatal error: refusing to overwrite the input file `foo.y'
+[foo.y: refusing to overwrite the input file `foo.y'
 ], 1)
 
 
diff --git a/tests/skeletons.at b/tests/skeletons.at
index f96d13e2..18acbc01 100644
--- a/tests/skeletons.at
+++ b/tests/skeletons.at
@@ -288,3 +288,45 @@ foo.y:1.5-6: fatal error: M4 should exit immediately here
 ]])
 
 AT_CLEANUP
+
+
+## ------------------------------------------------ ##
+## Fatal errors but M4 continues producing output.  ##
+## ------------------------------------------------ ##
+
+# At one time, if Bison encountered a fatal error during M4 processing,
+# Bison failed to drain M4's output pipe.  The result was a SIGPIPE.
+# On some platforms, the default disposition for SIGPIPE is terminate,
+# which was fine.  On others, it's ignore, which caused M4 to report
+# the broken pipe to the user, but we don't want to bother the user with
+# that.
+
+# There is a race condition somewhere.  That is, before the associated
+# fix, running this test group many times in a row would occasionally
+# produce a pass among all the failures.
+
+AT_SETUP([[Fatal errors but M4 continues producing output]])
+
+AT_DATA([[gen-skel.pl]],
+[[use warnings;
+use strict;
+my $M4 = "m4";
+my $DNL = "d"."nl";
+print "${M4}_divert_push(0)$DNL\n";
+print '@output(@,@)', "\n";
+(print "garbage"x10, "\n") for (1..1000);
+print "${M4}_divert_pop(0)\n";
+]])
+AT_CHECK([[perl gen-skel.pl > skel.c || exit 77]])
+
+AT_DATA([[input.y]],
+[[%skeleton "./skel.c"
+%%
+start: ;
+]])
+
+AT_BISON_CHECK([[input.y]], [[1]], [[]],
+[[input.y: fatal error: too many arguments for @output directive in skeleton
+]])
+
+AT_CLEANUP