qspawn: psgi_qx: delay callback until waitpid returns

We need to detect "git apply" failures reliably when patches
fail.  This is necessary for solving for blob 81c1164ae5 in
https://public-inbox.org/git/ when at least two messages can
solve for it (and one of them fails):

1. https://public-inbox.org/git/b9fb52b8-8168-6bf0-9a72-1e6c44a281a5@oracle.com/
2. https://public-inbox.org/git/56664222-6c29-09dc-ef78-7b380b113c4a@oracle.com/

1 files changed, 18 insertions, 12 deletions

diff --git a/lib/PublicInbox/Qspawn.pm b/lib/PublicInbox/Qspawn.pm
index cb3dc516..651fa390 100644
--- a/lib/PublicInbox/Qspawn.pm
+++ b/lib/PublicInbox/Qspawn.pm
@@ -106,17 +106,22 @@ sub waitpid_err ($$) {
                 }
         }
 
-        return unless $err;
-        $self->{err} = $err;
-        if ($env && !$env->{'qspawn.quiet'}) {
-                log_err($env, join(' ', @{$self->{args}}) . ": $err");
+        if ($err) {
+                $self->{err} = $err;
+                if ($env && !$env->{'qspawn.quiet'}) {
+                        log_err($env, join(' ', @{$self->{args}}) . ": $err");
+                }
+        }
+        if (my $fin_cb = delete $self->{fin_cb}) {
+                eval { $fin_cb->() }
         }
 }
 
-sub do_waitpid ($;$) {
-        my ($self, $env) = @_;
+sub do_waitpid ($;$$) {
+        my ($self, $env, $fin_cb) = @_;
         my $pid = $self->{pid};
         $self->{env} = $env;
+        $self->{fin_cb} = $fin_cb;
         # PublicInbox::DS may not be loaded
         eval { PublicInbox::DS::dwaitpid($pid, \&waitpid_err, $self) };
         # done if we're running in PublicInbox::DS::EventLoop
@@ -127,10 +132,12 @@ sub do_waitpid ($;$) {
         }
 }
 
-sub finish ($;$) {
-        my ($self, $env) = @_;
+sub finish ($;$$) {
+        my ($self, $env, $fin_cb) = @_;
         if (delete $self->{rpipe}) {
-                do_waitpid($self, $env);
+                do_waitpid($self, $env, $fin_cb);
+        } elsif ($fin_cb) {
+                eval { $fin_cb->() };
         }
 }
 
@@ -154,9 +161,8 @@ sub psgi_qx {
         my $end = sub {
                 my $err = $_[0]; # $!
                 log_err($env, "psgi_qx: $err") if defined($err);
-                finish($self, $env);
-                eval { $qx_cb->(\$scalar) };
-                $qx = $scalar = undef;
+                finish($self, $env, sub { $qx_cb->(\$scalar) });
+                $qx = undef;
         };
         my $rpipe; # comes from popen_rd
         my $async = $env->{'pi-httpd.async'};