Resurrect git-rerere to contrib/examples
It is handy to have a copy readily available for checking regressions.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/examples/git-rerere.perl b/contrib/examples/git-rerere.perl
new file mode 100755
index 0000000..4f69209
--- /dev/null
+++ b/contrib/examples/git-rerere.perl
@@ -0,0 +1,284 @@
+#!/usr/bin/perl
+#
+# REuse REcorded REsolve. This tool records a conflicted automerge
+# result and its hand resolution, and helps to resolve future
+# automerge that results in the same conflict.
+#
+# To enable this feature, create a directory 'rr-cache' under your
+# .git/ directory.
+
+use Digest;
+use File::Path;
+use File::Copy;
+
+my $git_dir = $::ENV{GIT_DIR} || ".git";
+my $rr_dir = "$git_dir/rr-cache";
+my $merge_rr = "$git_dir/rr-cache/MERGE_RR";
+
+my %merge_rr = ();
+
+sub read_rr {
+ if (!-f $merge_rr) {
+ %merge_rr = ();
+ return;
+ }
+ my $in;
+ local $/ = "\0";
+ open $in, "<$merge_rr" or die "$!: $merge_rr";
+ while (<$in>) {
+ chomp;
+ my ($name, $path) = /^([0-9a-f]{40})\t(.*)$/s;
+ $merge_rr{$path} = $name;
+ }
+ close $in;
+}
+
+sub write_rr {
+ my $out;
+ open $out, ">$merge_rr" or die "$!: $merge_rr";
+ for my $path (sort keys %merge_rr) {
+ my $name = $merge_rr{$path};
+ print $out "$name\t$path\0";
+ }
+ close $out;
+}
+
+sub compute_conflict_name {
+ my ($path) = @_;
+ my @side = ();
+ my $in;
+ open $in, "<$path" or die "$!: $path";
+
+ my $sha1 = Digest->new("SHA-1");
+ my $hunk = 0;
+ while (<$in>) {
+ if (/^<<<<<<< .*/) {
+ $hunk++;
+ @side = ([], undef);
+ }
+ elsif (/^=======$/) {
+ $side[1] = [];
+ }
+ elsif (/^>>>>>>> .*/) {
+ my ($one, $two);
+ $one = join('', @{$side[0]});
+ $two = join('', @{$side[1]});
+ if ($two le $one) {
+ ($one, $two) = ($two, $one);
+ }
+ $sha1->add($one);
+ $sha1->add("\0");
+ $sha1->add($two);
+ $sha1->add("\0");
+ @side = ();
+ }
+ elsif (@side == 0) {
+ next;
+ }
+ elsif (defined $side[1]) {
+ push @{$side[1]}, $_;
+ }
+ else {
+ push @{$side[0]}, $_;
+ }
+ }
+ close $in;
+ return ($sha1->hexdigest, $hunk);
+}
+
+sub record_preimage {
+ my ($path, $name) = @_;
+ my @side = ();
+ my ($in, $out);
+ open $in, "<$path" or die "$!: $path";
+ open $out, ">$name" or die "$!: $name";
+
+ while (<$in>) {
+ if (/^<<<<<<< .*/) {
+ @side = ([], undef);
+ }
+ elsif (/^=======$/) {
+ $side[1] = [];
+ }
+ elsif (/^>>>>>>> .*/) {
+ my ($one, $two);
+ $one = join('', @{$side[0]});
+ $two = join('', @{$side[1]});
+ if ($two le $one) {
+ ($one, $two) = ($two, $one);
+ }
+ print $out "<<<<<<<\n";
+ print $out $one;
+ print $out "=======\n";
+ print $out $two;
+ print $out ">>>>>>>\n";
+ @side = ();
+ }
+ elsif (@side == 0) {
+ print $out $_;
+ }
+ elsif (defined $side[1]) {
+ push @{$side[1]}, $_;
+ }
+ else {
+ push @{$side[0]}, $_;
+ }
+ }
+ close $out;
+ close $in;
+}
+
+sub find_conflict {
+ my $in;
+ local $/ = "\0";
+ my $pid = open($in, '-|');
+ die "$!" unless defined $pid;
+ if (!$pid) {
+ exec(qw(git ls-files -z -u)) or die "$!: ls-files";
+ }
+ my %path = ();
+ my @path = ();
+ while (<$in>) {
+ chomp;
+ my ($mode, $sha1, $stage, $path) =
+ /^([0-7]+) ([0-9a-f]{40}) ([123])\t(.*)$/s;
+ $path{$path} |= (1 << $stage);
+ }
+ close $in;
+ while (my ($path, $status) = each %path) {
+ if ($status == 14) { push @path, $path; }
+ }
+ return @path;
+}
+
+sub merge {
+ my ($name, $path) = @_;
+ record_preimage($path, "$rr_dir/$name/thisimage");
+ unless (system('git', 'merge-file', map { "$rr_dir/$name/${_}image" }
+ qw(this pre post))) {
+ my $in;
+ open $in, "<$rr_dir/$name/thisimage" or
+ die "$!: $name/thisimage";
+ my $out;
+ open $out, ">$path" or die "$!: $path";
+ while (<$in>) { print $out $_; }
+ close $in;
+ close $out;
+ return 1;
+ }
+ return 0;
+}
+
+sub garbage_collect_rerere {
+ # We should allow specifying these from the command line and
+ # that is why the caller gives @ARGV to us, but I am lazy.
+
+ my $cutoff_noresolve = 15; # two weeks
+ my $cutoff_resolve = 60; # two months
+ my @to_remove;
+ while (<$rr_dir/*/preimage>) {
+ my ($dir) = /^(.*)\/preimage$/;
+ my $cutoff = ((-f "$dir/postimage")
+ ? $cutoff_resolve
+ : $cutoff_noresolve);
+ my $age = -M "$_";
+ if ($cutoff <= $age) {
+ push @to_remove, $dir;
+ }
+ }
+ if (@to_remove) {
+ rmtree(\@to_remove);
+ }
+}
+
+-d "$rr_dir" || exit(0);
+
+read_rr();
+
+if (@ARGV) {
+ my $arg = shift @ARGV;
+ if ($arg eq 'clear') {
+ for my $path (keys %merge_rr) {
+ my $name = $merge_rr{$path};
+ if (-d "$rr_dir/$name" &&
+ ! -f "$rr_dir/$name/postimage") {
+ rmtree(["$rr_dir/$name"]);
+ }
+ }
+ unlink $merge_rr;
+ }
+ elsif ($arg eq 'status') {
+ for my $path (keys %merge_rr) {
+ print $path, "\n";
+ }
+ }
+ elsif ($arg eq 'diff') {
+ for my $path (keys %merge_rr) {
+ my $name = $merge_rr{$path};
+ system('diff', ((@ARGV == 0) ? ('-u') : @ARGV),
+ '-L', "a/$path", '-L', "b/$path",
+ "$rr_dir/$name/preimage", $path);
+ }
+ }
+ elsif ($arg eq 'gc') {
+ garbage_collect_rerere(@ARGV);
+ }
+ else {
+ die "$0 unknown command: $arg\n";
+ }
+ exit 0;
+}
+
+my %conflict = map { $_ => 1 } find_conflict();
+
+# MERGE_RR records paths with conflicts immediately after merge
+# failed. Some of the conflicted paths might have been hand resolved
+# in the working tree since then, but the initial run would catch all
+# and register their preimages.
+
+for my $path (keys %conflict) {
+ # This path has conflict. If it is not recorded yet,
+ # record the pre-image.
+ if (!exists $merge_rr{$path}) {
+ my ($name, $hunk) = compute_conflict_name($path);
+ next unless ($hunk);
+ $merge_rr{$path} = $name;
+ if (! -d "$rr_dir/$name") {
+ mkpath("$rr_dir/$name", 0, 0777);
+ print STDERR "Recorded preimage for '$path'\n";
+ record_preimage($path, "$rr_dir/$name/preimage");
+ }
+ }
+}
+
+# Now some of the paths that had conflicts earlier might have been
+# hand resolved. Others may be similar to a conflict already that
+# was resolved before.
+
+for my $path (keys %merge_rr) {
+ my $name = $merge_rr{$path};
+
+ # We could resolve this automatically if we have images.
+ if (-f "$rr_dir/$name/preimage" &&
+ -f "$rr_dir/$name/postimage") {
+ if (merge($name, $path)) {
+ print STDERR "Resolved '$path' using previous resolution.\n";
+ # Then we do not have to worry about this path
+ # anymore.
+ delete $merge_rr{$path};
+ next;
+ }
+ }
+
+ # Let's see if we have resolved it.
+ (undef, my $hunk) = compute_conflict_name($path);
+ next if ($hunk);
+
+ print STDERR "Recorded resolution for '$path'.\n";
+ copy($path, "$rr_dir/$name/postimage");
+ # And we do not have to worry about this path anymore.
+ delete $merge_rr{$path};
+}
+
+# Write out the rest.
+write_rr();
