favor git(1) rather than libgit2 for ExtSearch

While both git and libgit2 take around 16 minutes to load 100K
alternates there's already a proposed patch to make git faster:

  <https://lore.kernel.org/git/20210624005806.12079-1-e@80x24.org/>

It's also easier to patch and install git locally since the
git.git build system defaults to prefix=$HOME and dealing with
dynamic linking with libgit2 is more difficult for end users
relying on Inline::C.

libgit2 remains in use for the non-ALL.git case, but maybe it's
not necessary (libgit2 is significantly slower than git in
Debian 10 due to SHA-1 collision checking).

1 files changed, 13 insertions, 8 deletions

diff --git a/lib/PublicInbox/GitAsyncCat.pm b/lib/PublicInbox/GitAsyncCat.pm
index 7d1a13db..57c194d9 100644
--- a/lib/PublicInbox/GitAsyncCat.pm
+++ b/lib/PublicInbox/GitAsyncCat.pm
@@ -8,7 +8,7 @@ use strict;
 use parent qw(PublicInbox::DS Exporter);
 use POSIX qw(WNOHANG);
 use PublicInbox::Syscall qw(EPOLLIN EPOLLET);
-our @EXPORT = qw(git_async_cat git_async_prefetch);
+our @EXPORT = qw(ibx_async_cat ibx_async_prefetch);
 use PublicInbox::Git ();
 
 our $GCF2C; # singleton PublicInbox::Gcf2Client
@@ -45,12 +45,16 @@ sub event_step {
         }
 }
 
-sub git_async_cat ($$$$) {
-        my ($git, $oid, $cb, $arg) = @_;
-        if ($GCF2C //= eval {
+sub ibx_async_cat ($$$$) {
+        my ($ibx, $oid, $cb, $arg) = @_;
+        my $git = $ibx->git;
+        # {topdir} means ExtSearch (likely [extindex "all"]) with potentially
+        # 100K alternates.  git(1) has a proposed patch for 100K alternates:
+        # <https://lore.kernel.org/git/20210624005806.12079-1-e@80x24.org/>
+        if (!defined($ibx->{topdir}) && ($GCF2C //= eval {
                 require PublicInbox::Gcf2Client;
                 PublicInbox::Gcf2Client::new();
-        } // 0) { # 0: do not retry if libgit2 or Inline::C are missing
+        } // 0)) { # 0: do not retry if libgit2 or Inline::C are missing
                 $GCF2C->gcf2_async(\"$oid $git->{git_dir}\n", $cb, $arg);
                 \undef;
         } else { # read-only end of git-cat-file pipe
@@ -66,9 +70,10 @@ sub git_async_cat ($$$$) {
 
 # this is safe to call inside $cb, but not guaranteed to enqueue
 # returns true if successful, undef if not.
-sub git_async_prefetch {
-        my ($git, $oid, $cb, $arg) = @_;
-        if ($GCF2C) {
+sub ibx_async_prefetch {
+        my ($ibx, $oid, $cb, $arg) = @_;
+        my $git = $ibx->git;
+        if (!defined($ibx->{topdir}) && $GCF2C) {
                 if (!$GCF2C->{wbuf}) {
                         $oid .= " $git->{git_dir}\n";
                         return $GCF2C->gcf2_async(\$oid, $cb, $arg); # true