From 35786bae6f659ab4c0595c829e2b436e0c292d1c Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sat, 4 Jun 2016 17:10:17 +0100
Subject: [PATCH] Split brain: Memoise (cache) split brain dgit-view in a
 reflog

---
 dgit | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 74 insertions(+), 5 deletions(-)

diff --git a/dgit b/dgit
index 0812f32a..b22d6ab3 100755
--- a/dgit
+++ b/dgit
@@ -71,6 +71,7 @@ our $suite_re = '[-+.0-9a-z]+';
 our $cleanmode_re = 'dpkg-source(?:-d)?|git|git-ff|check|none';
 
 our $git_authline_re = '^([^<>]+) \<(\S+)\> (\d+ [-+]\d+)$';
+our $splitbraincache = 'dgit-intern/quilt-cache';
 
 our (@git) = qw(git);
 our (@dget) = qw(dget);
@@ -2556,8 +2557,9 @@ sub quiltify_splitbrain_needed () {
     }
 }
 
-sub quiltify_splitbrain ($$$$$) {
-    my ($clogp, $unapplied, $headref, $diffbits, $editedignores) = @_;
+sub quiltify_splitbrain ($$$$$$) {
+    my ($clogp, $unapplied, $headref, $diffbits,
+	$editedignores, $cachekey) = @_;
     if ($quilt_mode !~ m/gbp|dpm/) {
 	# treat .gitignore just like any other upstream file
 	$diffbits = { %$diffbits };
@@ -2613,8 +2615,17 @@ END
         commit_admin "Commit patch to update .gitignore";
     }
 
-    die 'xxx memoisation via git-reflog';
+    my $dgitview = git_rev_parse 'refs/heads/dgit-view';
+
+    changedir '../../../..';
+    ensuredir ".git/logs/refs/dgit-intern";
+    my $makelogfh = new IO::File ".git/logs/refs/$splitbraincache", '>>'
+      or die $!;
+    runcmd @git, qw(update-ref -m), $cachekey, "refs/$splitbraincache",
+	$dgitview;
+
     die 'xxx fast forward (should not depend on quilt mode, but will always be needed if we did $split_brain)';
+    changedir '.git/dgit/unpack/work';
 }
 
 sub quiltify ($$$$) {
@@ -3026,6 +3037,63 @@ END
     $dscaddfile->($debtar);
     close $fakedsc or die $!;
 
+    my $splitbrain_cachekey;
+    if ($quilt_mode =~ m/gbp|dpm|unapplied/) {
+	# we look in the reflog of dgit-intern/quilt-cache
+	# we look for an entry whose message is the key for the cache lookup
+	my @cachekey = (qw(dgit), $our_version);
+	push @cachekey, $upstreamversion;
+	push @cachekey, $headref;
+
+	push @cachekey, hashfile('fake.dsc');
+
+	my $srcshash = Digest::SHA->new(256);
+	my %sfs = ( %INC, '$0(dgit)' => $0 );
+	foreach my $sfk (sort keys %sfs) {
+	    $srcshash->add($sfk,"  ");
+	    $srcshash->add(hashfile($sfs{$sfk}));
+	    $srcshash->add("\n");
+	}
+	push @cachekey, $srcshash->hexdigest();
+	$splitbrain_cachekey = "@cachekey";
+
+	my @cmd = (@git, qw(reflog), '--pretty=format:%H %gs',
+		   $splitbraincache);
+	printdebug "splitbrain cachekey $splitbrain_cachekey\n";
+	debugcmd "|(probably)",@cmd;
+	my $child = open GC, "-|";  defined $child or die $!;
+	if (!$child) {
+	    chdir '../../..' or die $!;
+	    if (!stat ".git/logs/refs/$splitbraincache") {
+		$! == ENOENT or die $!;
+		printdebug ">(no reflog)\n";
+		exit 0;
+	    }
+	    exec @cmd; die $!;
+	}
+	while (<GC>) {
+	    chomp;
+	    printdebug ">| ", $_, "\n" if $debuglevel > 1;
+	    next unless m/^(\w+) (\S.*\S)$/ && $2 eq $splitbrain_cachekey;
+	    
+	    my $cachehit = $1;
+	    quilt_fixup_mkwork($headref);
+	    if ($cachehit ne $headref) {
+		progress "quilt fixup ($quilt_mode mode) found cached tree";
+		runcmd @git, qw(checkout -q -b dgit-view), $cachehit;
+		$split_brain = 1;
+		return;
+	    }
+	    progress "quilt fixup ($quilt_mode mode)".
+	      " found cached indication that no changes needed";
+	    return;
+	}
+	die $! if GC->error;
+	failedcmd unless close GC;
+
+	printdebug "splitbrain cache miss\n";
+    }
+
     runcmd qw(sh -ec),
         'exec dpkg-source --no-check --skip-patches -x fake.dsc >/dev/null';
 
@@ -3105,9 +3173,10 @@ END
     push @failsuggestion, "Maybe you need to specify one of".
         " --quilt=gbp --quilt=dpm --quilt=unapplied ?";
 
-    if ($quilt_mode =~ m/gbp|dpm|unapplied/) {
+    if ($splitbrain_cachekey) {
 	quiltify_splitbrain($clogp, $unapplied, $headref,
-                            $diffbits, \%editedignores);
+                            $diffbits, \%editedignores,
+			    $splitbrain_cachekey);
 	return;
     }
 
-- 
2.30.2