[PATCH] spawn+gcf2: improve diagnostics for build failures

[Eric Wong <e@80x24.org>]

I'm not sure why, but I noticed the one of my latest restarts of
public-inbox-httpd wasn't loading the Inline::C .so for Gcf2 nor
Spawn.  I also can't reproduce the problem as both .so files are
loaded fine on a restart with zero config changes.

In any case, some extra, automatic diagnostics for build errors
won't hurt, as no extra noise is introduced for successful builds.
This will also make future development of C code more convenient,
hopefully.
---
 lib/PublicInbox/Gcf2.pm  | 39 ++++++++++------
 lib/PublicInbox/Spawn.pm | 96 ++++++++++++++++++++++------------------
 2 files changed, 80 insertions(+), 55 deletions(-)

diff --git a/lib/PublicInbox/Gcf2.pm b/lib/PublicInbox/Gcf2.pm
index 0f967579..0d31b014 100644
--- a/lib/PublicInbox/Gcf2.pm
+++ b/lib/PublicInbox/Gcf2.pm
@@ -7,16 +7,16 @@ package PublicInbox::Gcf2;
 use strict;
 use v5.10.1;
 use PublicInbox::Spawn qw(which popen_rd); # may set PERL_INLINE_DIRECTORY
-use Fcntl qw(LOCK_EX);
+use Fcntl qw(LOCK_EX SEEK_SET);
 use IO::Handle; # autoflush
-my (%CFG, $c_src, $lockfh);
 BEGIN {
+	my (%CFG, $c_src);
 	# PublicInbox::Spawn will set PERL_INLINE_DIRECTORY
 	# to ~/.cache/public-inbox/inline-c if it exists
 	my $inline_dir = $ENV{PERL_INLINE_DIRECTORY} //
 		die 'PERL_INLINE_DIRECTORY not defined';
 	my $f = "$inline_dir/.public-inbox.lock";
-	open $lockfh, '>', $f or die "failed to open $f: $!\n";
+	open my $fh, '+>', $f or die "open($f): $!";
 	my $pc = which($ENV{PKG_CONFIG} // 'pkg-config') //
 		die "pkg-config missing for libgit2";
 	my ($dir) = (__FILE__ =~ m!\A(.+?)/[^/]+\z!);
@@ -37,27 +37,40 @@ BEGIN {
 		if (open(my $fh, '<', $f)) {
 			chomp($l, $c);
 			local $/;
-			defined($c_src = <$fh>) or die "read $f: $!\n";
+			defined($c_src = <$fh>) or die "read $f: $!";
 			$CFG{LIBS} = $l;
 			$CFG{CCFLAGSEX} = $c;
 			last;
 		} else {
-			die "E: $f: $!\n";
+			die "E: $f: $!";
 		}
 	}
 	die "E: libgit2 not installed\n" unless $c_src;
 
+	open my $oldout, '>&', \*STDOUT or die "dup(1): $!";
+	open my $olderr, '>&', \*STDERR or die "dup(2): $!";
+	open STDOUT, '>&', $fh or die "1>$f: $!";
+	open STDERR, '>&', $fh or die "2>$f: $!";
+	STDERR->autoflush(1);
+	STDOUT->autoflush(1);
+
 	# CentOS 7.x ships Inline 0.53, 0.64+ has built-in locking
-	flock($lockfh, LOCK_EX) or die "LOCK_EX failed on $f: $!\n";
+	flock($fh, LOCK_EX) or die "LOCK_EX($f): $!\n";
+	# we use Capitalized and ALLCAPS for compatibility with old Inline::C
+	eval <<'EOM';
+use Inline C => Config => %CFG, BOOT => q[git_libgit2_init();];
+use Inline C => $c_src, BUILD_NOISY => 1;
+EOM
+	my $err = $@;
+	open(STDERR, '>&', $olderr) or warn "restore stderr: $!";
+	open(STDOUT, '>&', $oldout) or warn "restore stdout: $!";
+	if ($err) {
+		seek($fh, 0, SEEK_SET);
+		my @msg = <$fh>;
+		die "Inline::C Gcf2 build failed:\n", $err, "\n", @msg;
+	}
 }
 
-# we use Capitalized and ALLCAPS for compatibility with old Inline::C
-use Inline C => Config => %CFG, BOOT => 'git_libgit2_init();';
-use Inline C => $c_src;
-undef $c_src;
-undef %CFG;
-undef $lockfh;
-
 sub add_alt ($$) {
 	my ($gcf2, $objdir) = @_;
 
diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index fe7aa0a8..e940d3c9 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -18,11 +18,14 @@ package PublicInbox::Spawn;
 use strict;
 use parent qw(Exporter);
 use Symbol qw(gensym);
+use Fcntl qw(LOCK_EX SEEK_SET);
+use IO::Handle ();
 use PublicInbox::ProcessPipe;
 our @EXPORT_OK = qw(which spawn popen_rd run_die nodatacow_dir);
 our @RLIMITS = qw(RLIMIT_CPU RLIMIT_CORE RLIMIT_DATA);
 
-my $all_libc = <<'ALL_LIBC'; # all *nix systems we support
+BEGIN {
+	my $all_libc = <<'ALL_LIBC'; # all *nix systems we support
 #include <sys/resource.h>
 #include <sys/socket.h>
 #include <sys/types.h>
@@ -249,7 +252,7 @@ ALL_LIBC
 # directories.  Disabling COW disables checksumming, so we only do this
 # for regeneratable files, and not canonical git storage (git doesn't
 # checksum refs, only data under $GIT_DIR/objects).
-my $set_nodatacow = $^O eq 'linux' ? <<'SET_NODATACOW' : '';
+	my $set_nodatacow = $^O eq 'linux' ? <<'SET_NODATACOW' : '';
 #include <sys/ioctl.h>
 #include <sys/vfs.h>
 #include <linux/magic.h>
@@ -296,52 +299,61 @@ void nodatacow_dir(const char *dir)
 }
 SET_NODATACOW
 
-my $inline_dir = $ENV{PERL_INLINE_DIRECTORY} //= (
-		$ENV{XDG_CACHE_HOME} //
-		( ($ENV{HOME} // '/nonexistent').'/.cache' )
-	).'/public-inbox/inline-c';
-
-$set_nodatacow = $all_libc = undef unless -d $inline_dir && -w _;
-if (defined $all_libc) {
-	# Inline 0.64 or later has locking in multi-process env,
-	# but we support 0.5 on Debian wheezy
-	use Fcntl qw(:flock);
-	eval {
+	my $inline_dir = $ENV{PERL_INLINE_DIRECTORY} //= (
+			$ENV{XDG_CACHE_HOME} //
+			( ($ENV{HOME} // '/nonexistent').'/.cache' )
+		).'/public-inbox/inline-c';
+	warn "$inline_dir exists, not writable\n" if -e $inline_dir && !-w _;
+	$set_nodatacow = $all_libc = undef unless -d _ && -w _;
+	if (defined $all_libc) {
 		my $f = "$inline_dir/.public-inbox.lock";
-		open my $fh, '>', $f or die "failed to open $f: $!\n";
-		flock($fh, LOCK_EX) or die "LOCK_EX failed on $f: $!\n";
-		eval 'use Inline C => $all_libc.$set_nodatacow';
-			# . ', BUILD_NOISY => 1';
+		open my $oldout, '>&', \*STDOUT or die "dup(1): $!";
+		open my $olderr, '>&', \*STDERR or die "dup(2): $!";
+		open my $fh, '+>', $f or die "open($f): $!";
+		open STDOUT, '>&', $fh or die "1>$f: $!";
+		open STDERR, '>&', $fh or die "2>$f: $!";
+		STDERR->autoflush(1);
+		STDOUT->autoflush(1);
+
+		# CentOS 7.x ships Inline 0.53, 0.64+ has built-in locking
+		flock($fh, LOCK_EX) or die "LOCK_EX($f): $!";
+		eval <<'EOM';
+use Inline C => $all_libc.$set_nodatacow, BUILD_NOISY => 1;
+EOM
 		my $err = $@;
-		my $ndc_err;
+		my $ndc_err = '';
 		if ($err && $set_nodatacow) { # missing Linux kernel headers
-			$ndc_err = $err;
+			$ndc_err = "with set_nodatacow: <\n$err\n>\n";
 			undef $set_nodatacow;
-			eval 'use Inline C => $all_libc';
+			eval <<'EOM';
+use Inline C => $all_libc, BUILD_NOISY => 1;
+EOM
+		};
+		$err = $@;
+		open(STDERR, '>&', $olderr) or warn "restore stderr: $!";
+		open(STDOUT, '>&', $oldout) or warn "restore stdout: $!";
+		if ($err) {
+			seek($fh, 0, SEEK_SET);
+			my @msg = <$fh>;
+			warn "Inline::C build failed:\n",
+				$ndc_err, $err, "\n", @msg;
+			$set_nodatacow = $all_libc = undef;
+		} elsif ($ndc_err) {
+			warn "Inline::C build succeeded w/o set_nodatacow\n",
+				"error $ndc_err";
 		}
-		flock($fh, LOCK_UN) or die "LOCK_UN failed on $f: $!\n";
-		die $err if $err;
-		warn $ndc_err if $ndc_err;
-	};
-	if ($@) {
-		warn "Inline::C failed for vfork: $@\n";
-		$set_nodatacow = $all_libc = undef;
 	}
-}
-
-unless ($all_libc) {
-	require PublicInbox::SpawnPP;
-	*pi_fork_exec = \&PublicInbox::SpawnPP::pi_fork_exec
-}
-unless ($set_nodatacow) {
-	require PublicInbox::NDC_PP;
-	no warnings 'once';
-	*nodatacow_fd = \&PublicInbox::NDC_PP::nodatacow_fd;
-	*nodatacow_dir = \&PublicInbox::NDC_PP::nodatacow_dir;
-}
-
-undef $set_nodatacow;
-undef $all_libc;
+	unless ($all_libc) {
+		require PublicInbox::SpawnPP;
+		*pi_fork_exec = \&PublicInbox::SpawnPP::pi_fork_exec
+	}
+	unless ($set_nodatacow) {
+		require PublicInbox::NDC_PP;
+		no warnings 'once';
+		*nodatacow_fd = \&PublicInbox::NDC_PP::nodatacow_fd;
+		*nodatacow_dir = \&PublicInbox::NDC_PP::nodatacow_dir;
+	}
+} # /BEGIN
 
 sub which ($) {
 	my ($file) = @_;