gcf2: detect libgit2 version changes

We need to force Inline::C to rebuild if libgit2 is updated;
otherwise dynamic linking can be broken.  Adding the output
from the `--modversion' of pkg-config(1) along with the existing
`--libs' and `--cflags' output seems appropriate for this task.

To force Inline::C into a rebuild, neither CFLAGSEX nor CPPFLAGS
changes are enough.  Modifying the source string and adding
comments seems like the most obvious way to force a rebuild.

The `-print-file-name=LIBRARY' feature from gcc+clang could also
be used, but that requires parsing the library name from
`pkg-config --libs' output into a library basename appropriate
for `-print-file-name='.  IOW, we'd need to transform:
`-lgit2' => `libgit2.so'; and possibly deal with platforms
which deal with static libraries in the future.

So just use pkg-config, since `pkg-config --modversion' is
roughly 2-3x as fast as `gcc-10 -print-file-name=', and
10-20x faster than clang-11.

1 files changed, 18 insertions, 18 deletions

diff --git a/lib/PublicInbox/Gcf2.pm b/lib/PublicInbox/Gcf2.pm
index d13e6b1a..9ca99d00 100644
--- a/lib/PublicInbox/Gcf2.pm
+++ b/lib/PublicInbox/Gcf2.pm
@@ -4,8 +4,7 @@
 # backend for a git-cat-file-workalike based on libgit2,
 # other libgit2 stuff may go here, too.
 package PublicInbox::Gcf2;
-use strict;
-use v5.10.1;
+use v5.12;
 use PublicInbox::Spawn qw(which popen_rd); # may set PERL_INLINE_DIRECTORY
 use Fcntl qw(LOCK_EX SEEK_SET);
 use Time::HiRes qw(clock_gettime CLOCK_MONOTONIC);
@@ -29,40 +28,41 @@ BEGIN {
         my ($dir) = (__FILE__ =~ m!\A(.+?)/[^/]+\z!);
         my $ef = "$inline_dir/.public-inbox.pkg-config.err";
         open my $err, '+>', $ef or die "open($ef): $!";
-        for my $x (qw(libgit2)) {
-                my $rdr = { 2 => $err };
-                my ($l, $pid) = popen_rd([$pc, '--libs', $x], undef, $rdr);
-                $l = do { local $/; <$l> };
-                waitpid($pid, 0);
-                next if $?;
-                (my $c, $pid) = popen_rd([$pc, '--cflags', $x], undef, $rdr);
-                $c = do { local $/; <$c> };
-                waitpid($pid, 0);
-                next if $?;
-
+        my $vals = {};
+        my $rdr = { 2 => $err };
+        my @switches = qw(modversion cflags libs);
+        for my $k (@switches) {
+                my $rd = popen_rd([$pc, "--$k", 'libgit2'], undef, $rdr);
+                chomp(my $val = do { local $/; <$rd> });
+                close($rd) or last; # checks for error and sets $?
+                $vals->{$k} = $val;
+        }
+        if (!$?) {
                 # note: we name C source files .h to prevent
                 # ExtUtils::MakeMaker from automatically trying to
                 # build them.
-                my $f = "$dir/gcf2_$x.h";
+                my $f = "$dir/gcf2_libgit2.h";
                 open(my $src, '<', $f) or die "E: open($f): $!";
-                chomp($l, $c);
                 local $/;
                 defined($c_src = <$src>) or die "read $f: $!";
-                $CFG{LIBS} = $l;
-                $CFG{CCFLAGSEX} = $c;
-                last;
         }
         unless ($c_src) {
                 seek($err, 0, SEEK_SET);
                 $err = do { local $/; <$err> };
                 die "E: libgit2 not installed: $err\n";
         }
+        # append pkg-config results to the source to ensure Inline::C
+        # can rebuild if there's changes (it doesn't seem to detect
+        # $CFG{CCFLAGSEX} nor $CFG{CPPFLAGS} changes)
+        $c_src .= "/* $pc --$_ libgit2 => $vals->{$_} */\n" for @switches;
         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);
+        $CFG{CCFLAGSEX} = $vals->{cflags};
+        $CFG{LIBS} = $vals->{libs};
 
         # we use Capitalized and ALLCAPS for compatibility with old Inline::C
         eval <<'EOM';