[PATCH 04/37] solver: initial Perl implementation

[Eric Wong <e@80x24.org>]

This will lookup git blobs from associated git source code
repositories.  If the blobs can't be found, an attempt to
"solve" them via patch application will be performed.

Eventually, this may become the basis of a type-agnostic
frontend similar to "git show"
---
 MANIFEST                                     |   4 +
 lib/PublicInbox/Git.pm                       |  16 +
 lib/PublicInbox/SolverGit.pm                 | 400 +++++++++++++++++++
 t/solve/0001-simple-mod.patch                |  20 +
 t/solve/0002-rename-with-modifications.patch |  37 ++
 t/solver_git.t                               |  91 +++++
 6 files changed, 568 insertions(+)
 create mode 100644 lib/PublicInbox/SolverGit.pm
 create mode 100644 t/solve/0001-simple-mod.patch
 create mode 100644 t/solve/0002-rename-with-modifications.patch
 create mode 100644 t/solver_git.t

diff --git a/MANIFEST b/MANIFEST
index dfd9e27..95ad0c6 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -101,6 +101,7 @@ lib/PublicInbox/SearchIdxPart.pm
 lib/PublicInbox/SearchMsg.pm
 lib/PublicInbox/SearchThread.pm
 lib/PublicInbox/SearchView.pm
+lib/PublicInbox/SolverGit.pm
 lib/PublicInbox/Spamcheck.pm
 lib/PublicInbox/Spamcheck/Spamc.pm
 lib/PublicInbox/Spawn.pm
@@ -201,6 +202,9 @@ t/qspawn.t
 t/reply.t
 t/search-thr-index.t
 t/search.t
+t/solve/0001-simple-mod.patch
+t/solve/0002-rename-with-modifications.patch
+t/solver_git.t
 t/spamcheck_spamc.t
 t/spawn.t
 t/thread-cycle.t
diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
index 90b9214..9676086 100644
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -40,6 +40,7 @@ sub new {
 	my ($class, $git_dir) = @_;
 	my @st;
 	$st[7] = $st[10] = 0;
+	# may contain {-wt} field (working-tree (File::Temp::Dir))
 	bless { git_dir => $git_dir, st => \@st }, $class
 }
 
@@ -201,6 +202,21 @@ sub packed_bytes {
 
 sub DESTROY { cleanup(@_) }
 
+# show the blob URL for cgit/gitweb/whatever
+sub src_blob_url {
+	my ($self, $oid) = @_;
+	# blob_fmt = "https://example.com/foo.git/blob/%s"
+	if (my $bfu = $self->{blob_fmt_url}) {
+		return sprintf($bfu, $oid);
+	}
+
+	# don't show full FS path, basename should be OK:
+	if ($self->{git_dir} =~ m!/([^/]+)\z!) {
+		return "/path/to/$1";
+	}
+	'???';
+}
+
 1;
 __END__
 =pod
diff --git a/lib/PublicInbox/SolverGit.pm b/lib/PublicInbox/SolverGit.pm
new file mode 100644
index 0000000..f28768a
--- /dev/null
+++ b/lib/PublicInbox/SolverGit.pm
@@ -0,0 +1,400 @@
+# Copyright (C) 2019 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# "Solve" blobs which don't exist in git code repositories by
+# searching inboxes for post-image blobs.
+
+# this emits a lot of debugging/tracing information which may be
+# publically viewed over HTTP(S).  Be careful not to expose
+# local filesystem layouts in the process.
+package PublicInbox::SolverGit;
+use strict;
+use warnings;
+use File::Temp qw();
+use Fcntl qw(SEEK_SET);
+use File::Path qw(make_path);
+use PublicInbox::Git qw(git_unquote);
+use PublicInbox::Spawn qw(spawn popen_rd);
+use PublicInbox::MsgIter qw(msg_iter msg_part_text);
+use URI::Escape qw(uri_escape_utf8);
+
+# don't bother if somebody sends us a patch with these path components,
+# it's junk at best, an attack attempt at worse:
+my %bad_component = map { $_ => 1 } ('', '.', '..');
+
+sub new {
+	my ($class, $gits, $inboxes) = @_;
+	bless {
+		gits => $gits,
+		inboxes => $inboxes,
+	}, $class;
+}
+
+# look for existing blobs already in git repos
+sub solve_existing ($$) {
+	my ($self, $want) = @_;
+	foreach my $git (@{$self->{gits}}) {
+		my ($oid_full, $type, $size) = $git->check($want->{oid_b});
+		if (defined($type) && $type eq 'blob') {
+			return [ $git, $oid_full, $type, int($size) ];
+		}
+	}
+	undef;
+}
+
+# returns a hashref with information about a diff:
+# {
+#	oid_a => abbreviated pre-image oid,
+#	oid_b => abbreviated post-image oid,
+#	tmp => anonymous file handle with the diff,
+#	hdr_lines => arrayref of various header lines for mode information
+#	mode_a => original mode of oid_a (string, not integer),
+#	ibx => PublicInbox::Inbox object containing the diff
+#	smsg => PublicInbox::SearchMsg object containing diff
+#	path_a => pre-image path
+#	path_b => post-image path
+# }
+sub extract_diff ($$$$) {
+	my ($p, $re, $ibx, $smsg) = @_;
+	my ($part) = @$p; # ignore $depth and @idx;
+	my $hdr_lines; # diff --git a/... b/...
+	my $tmp;
+	my $ct = $part->content_type || 'text/plain';
+	my ($s, undef) = msg_part_text($part, $ct);
+	defined $s or return;
+	my $di = {};
+	foreach my $l (split(/^/m, $s)) {
+		if ($l =~ /$re/) {
+			$di->{oid_a} = $1;
+			$di->{oid_b} = $2;
+			my $mode_a = $3;
+			if ($mode_a =~ /\A(?:100644|120000|100755)\z/) {
+				$di->{mode_a} = $mode_a;
+			}
+
+			# start writing the diff out to a tempfile
+			open($tmp, '+>', undef) or die "open(tmp): $!";
+			$di->{tmp} = $tmp;
+			$di->{hdr_lines} = $hdr_lines;
+
+			print $tmp @$hdr_lines, $l or die "print(tmp): $!";
+
+			# for debugging/diagnostics:
+			$di->{ibx} = $ibx;
+			$di->{smsg} = $smsg;
+		} elsif ($l =~ m!\Adiff --git ("?a/.+) ("?b/.+)$!) {
+			return $di if $tmp; # got our blob, done!
+
+			my ($path_a, $path_b) = ($1, $2);
+
+			# don't care for leading 'a/' and 'b/'
+			my (undef, @a) = split(m{/}, git_unquote($path_a));
+			my (undef, @b) = split(m{/}, git_unquote($path_b));
+
+			# get rid of path-traversal attempts and junk patches:
+			foreach (@a, @b) {
+				return if $bad_component{$_};
+			}
+
+			$di->{path_a} = join('/', @a);
+			$di->{path_b} = join('/', @b);
+			$hdr_lines = [ $l ];
+		} elsif ($tmp) {
+			print $tmp $l or die "print(tmp): $!";
+		} elsif ($hdr_lines) {
+			push @$hdr_lines, $l;
+		}
+	}
+	$tmp ? $di : undef;
+}
+
+sub path_searchable ($) { defined($_[0]) && $_[0] =~ m!\A[\w/\. \-]+\z! }
+
+sub find_extract_diff ($$$) {
+	my ($self, $ibx, $want) = @_;
+	my $srch = $ibx->search or return;
+
+	my $post = $want->{oid_b} or die 'BUG: no {oid_b}';
+	$post =~ /\A[a-f0-9]+\z/ or die "BUG: oid_b not hex: $post";
+
+	my $q = "dfpost:$post";
+	my $pre = $want->{oid_a};
+	if (defined $pre && $pre =~ /\A[a-f0-9]+\z/) {
+		$q .= " dfpre:$pre";
+	} else {
+		$pre = '[a-f0-9]{7}'; # for $re below
+	}
+
+	my $path_b = $want->{path_b};
+	if (path_searchable($path_b)) {
+		$q .= qq{ dfn:"$path_b"};
+
+		my $path_a = $want->{path_a};
+		if (path_searchable($path_a) && $path_a ne $path_b) {
+			$q .= qq{ dfn:"$path_a"};
+		}
+	}
+
+	my $msgs = $srch->query($q, { relevance => 1 });
+	my $re = qr/\Aindex ($pre[a-f0-9]*)\.\.($post[a-f0-9]*)(?: (\d+))?/;
+
+	my $di;
+	foreach my $smsg (@$msgs) {
+		$ibx->smsg_mime($smsg) or next;
+		msg_iter(delete($smsg->{mime}), sub {
+			$di ||= extract_diff($_[0], $re, $ibx, $smsg);
+		});
+		return $di if $di;
+	}
+}
+
+# pure Perl "git init"
+sub do_git_init_wt ($) {
+	my ($self) = @_;
+	my $wt = File::Temp->newdir('solver.wt-XXXXXXXX', TMPDIR => 1);
+	my $dir = $wt->dirname;
+
+	foreach (qw(objects/info refs/heads)) {
+		make_path("$dir/.git/$_") or die "make_path $_: $!";
+	}
+	open my $fh, '>', "$dir/.git/config" or die "open .git/config: $!";
+	print $fh <<'EOF' or die "print .git/config $!";
+[core]
+	repositoryFormatVersion = 0
+	filemode = true
+	bare = false
+	fsyncObjectfiles = false
+	logAllRefUpdates = false
+EOF
+	close $fh or die "close .git/config: $!";
+
+	open $fh, '>', "$dir/.git/HEAD" or die "open .git/HEAD: $!";
+	print $fh "ref: refs/heads/master\n" or die "print .git/HEAD: $!";
+	close $fh or die "close .git/HEAD: $!";
+
+	my $f = '.git/objects/info/alternates';
+	open $fh, '>', "$dir/$f" or die "open: $f: $!";
+	foreach my $git (@{$self->{gits}}) {
+		print $fh "$git->{git_dir}/objects\n" or die "print $f: $!";
+	}
+	close $fh or die "close: $f: $!";
+	$wt;
+}
+
+sub extract_old_mode ($) {
+	my ($di) = @_;
+	if (grep(/\Aold mode (100644|100755|120000)$/, @{$di->{hdr_lines}})) {
+		return $1;
+	}
+	'100644';
+}
+
+sub reap ($$) {
+	my ($pid, $msg) = @_;
+	waitpid($pid, 0) == $pid or die "waitpid($msg): $!";
+	$? == 0 or die "$msg failed: $?";
+}
+
+sub prepare_wt ($$$) {
+	my ($wt_dir, $existing, $di) = @_;
+	my $oid_full = $existing->[1];
+	my ($r, $w);
+	my $path_a = $di->{path_a} or die "BUG: path_a missing for $oid_full";
+	my $mode_a = $di->{mode_a} || extract_old_mode($di);
+	my @git = (qw(git -C), $wt_dir);
+
+	pipe($r, $w) or die "pipe: $!";
+	my $rdr = { 0 => fileno($r) };
+	my $pid = spawn([@git, qw(update-index -z --index-info)], {}, $rdr);
+	close $r or die "close pipe(r): $!";
+	print $w "$mode_a $oid_full\t$path_a\0" or die "print update-index: $!";
+	close $w or die "close update-index: $!";
+	reap($pid, 'update-index -z --index-info');
+
+	$pid = spawn([@git, qw(checkout-index -a -f -u)]);
+	reap($pid, 'checkout-index -a -f -u');
+}
+
+sub do_apply ($$$$) {
+	my ($out, $wt_git, $wt_dir, $di) = @_;
+
+	my $tmp = delete $di->{tmp} or die "BUG: no tmp ", di_info($di);
+	$tmp->flush or die "tmp->flush failed: $!";
+	$out->flush or die "err->flush failed: $!";
+	sysseek($tmp, 0, SEEK_SET) or die "sysseek(tmp) failed: $!";
+
+	defined(my $err_fd = fileno($out)) or die "fileno(out): $!";
+	my $rdr = { 0 => fileno($tmp), 1 => $err_fd, 2 => $err_fd };
+	my $cmd = [ qw(git -C), $wt_dir,
+	            qw(apply --whitespace=warn -3 --verbose) ];
+	reap(spawn($cmd, undef, $rdr), 'apply');
+
+	local $/ = "\0";
+	my $rd = popen_rd([qw(git -C), $wt_dir, qw(ls-files -s -z)]);
+
+	defined(my $line = <$rd>) or die "failed to read ls-files: $!";
+	chomp $line or die "no trailing \\0 in [$line] from ls-files";
+
+	my ($info, $file) = split(/\t/, $line, 2);
+	my ($mode_b, $oid_b_full, $stage) = split(/ /, $info);
+
+	defined($line = <$rd>) and die "extra files in index: $line";
+	close $rd or die "close ls-files: $?";
+
+	$file eq $di->{path_b} or
+		die "index mismatch: file=$file != path_b=$di->{path_b}";
+	my $abs_path = "$wt_dir/$file";
+	-r $abs_path or die "WT_DIR/$file not readable";
+	my $size = -s _;
+
+	print $out "OK $mode_b $oid_b_full $stage\t$file\n";
+	[ $wt_git, $oid_b_full, 'blob', $size, $di ];
+}
+
+sub di_url ($) {
+	my ($di) = @_;
+	# note: we don't pass the PSGI env here, different inboxes
+	# can have different HTTP_HOST on the same instance.
+	my $url = $di->{ibx}->base_url;
+	my $mid = $di->{smsg}->{mid};
+	defined($url) ? "<$url/$mid/>" : "<$mid>";
+}
+
+sub apply_patches ($$$$$) {
+	my ($self, $out, $wt, $found, $patches) = @_;
+	my $wt_dir = $wt->dirname;
+	my $wt_git = PublicInbox::Git->new("$wt_dir/.git");
+	$wt_git->{-wt} = $wt;
+
+	my $cur = 0;
+	my $tot = scalar @$patches;
+
+	foreach my $di (@$patches) {
+		my $i = ++$cur;
+		my $oid_a = $di->{oid_a};
+		my $existing = $found->{$oid_a};
+		my $empty_oid = $oid_a =~ /\A0+\z/;
+
+		if ($empty_oid && $i != 0) {
+			die "empty oid at [$i/$tot] ", di_url($di);
+		}
+		if (!$existing && !$empty_oid) {
+			die "missing $oid_a at [$i/$tot] ", di_url($di);
+		}
+
+		# prepare the worktree for patch application:
+		if ($i == 1 && $existing) {
+			prepare_wt($wt_dir, $existing, $di);
+		}
+		unless (-f "$wt_dir/$di->{path_a}") {
+			die "missing $di->{path_a} at [$i/$tot] ", di_url($di);
+		}
+
+		print $out "applying [$i/$tot] ", di_url($di), "\n",
+			   join('', @{$di->{hdr_lines}}), "\n"
+			or die "print \$out failed: $!";
+
+		# apply the patch!
+		$found->{$di->{oid_b}} = do_apply($out, $wt_git, $wt_dir, $di);
+	}
+}
+
+sub dump_found ($$) {
+	my ($out, $found) = @_;
+	foreach my $oid (sort keys %$found) {
+		my ($git, $oid, $di) = @{$found->{$oid}};
+		my $loc = $di ? di_info($di) : $git->src_blob_url($oid);
+		print $out "$oid from $loc\n";
+	}
+}
+
+sub dump_patches ($$) {
+	my ($out, $patches) = @_;
+	my $tot = scalar(@$patches);
+	my $i = 0;
+	foreach my $di (@$patches) {
+		++$i;
+		print $out "[$i/$tot] ", di_url($di), "\n";
+	}
+}
+
+# recreate $oid_b
+# Returns a 2-element array ref: [ PublicInbox::Git object, oid_full ]
+# or undef if nothing was found.
+sub solve ($$$$) {
+	my ($self, $out, $oid_b, $hints) = @_;
+
+	# should we even get here? Probably not, but somebody
+	# could be manually typing URLs:
+	return if $oid_b =~ /\A0+\z/;
+
+	my $req = { %$hints, oid_b => $oid_b };
+	my @todo = ($req);
+	my $found = {}; # { oid_abbrev => [ PublicInbox::Git, oid_full, $di ] }
+	my $patches = []; # [ array of $di hashes ]
+
+	my $max = $self->{max_steps} || 200;
+	my $steps = 0;
+
+	while (defined(my $want = pop @todo)) {
+		# see if we can find the blob in an existing git repo:
+		if (my $existing = solve_existing($self, $want)) {
+			my $want_oid = $want->{oid_b};
+			return $existing if $want_oid eq $oid_b; # DONE!
+
+			$found->{$want_oid} = $existing;
+			next; # ok, one blob resolved, more to go?
+		}
+
+		# scan through inboxes to look for emails which results in
+		# the oid we want:
+		foreach my $ibx (@{$self->{inboxes}}) {
+			my $di = find_extract_diff($self, $ibx, $want) or next;
+
+			unshift @$patches, $di;
+
+			# good, we can find a path to the oid we $want, now
+			# lets see if we need to apply more patches:
+			my $src = $di->{oid_a};
+			if ($src !~ /\A0+\z/) {
+				if (++$steps > $max) {
+					print $out
+"Aborting, too many steps to $oid_b\n";
+
+					return;
+				}
+
+				# we have to solve it using another oid, fine:
+				my $job = {
+					oid_b => $src,
+					path_b => $di->{path_a},
+				};
+				push @todo, $job;
+			}
+			last; # onto the next @todo item
+		}
+	}
+
+	unless (scalar(@$patches)) {
+		print $out "no patch(es) for $oid_b\n";
+		dump_found($out, $found);
+		return;
+	}
+
+	# reconstruct the oid_b blob using patches we found:
+	eval {
+		my $wt = do_git_init_wt($self);
+		apply_patches($self, $out, $wt, $found, $patches);
+	};
+	if ($@) {
+		print $out "E: $@\nfound: ";
+		dump_found($out, $found);
+		print $out "patches: ";
+		dump_patches($out, $patches);
+		return;
+	}
+
+	$found->{$oid_b};
+}
+
+1;
diff --git a/t/solve/0001-simple-mod.patch b/t/solve/0001-simple-mod.patch
new file mode 100644
index 0000000..c6bb157
--- /dev/null
+++ b/t/solve/0001-simple-mod.patch
@@ -0,0 +1,20 @@
+From: WEB DESIGN EXPERT <BOFH@YHBT.net>
+To: meta@public-inbox.org
+Subject: [PATCH] TODO: take expert web design advice
+Date: Mon, 1 Apr 2019 08:15:20 +0000
+Message-Id: <20190401081523.16213-1-BOFH@YHBT.net>
+
+---
+ TODO | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/TODO b/TODO
+index 605013e..69df7d5 100644
+--- a/TODO
++++ b/TODO
+@@ -109,3 +109,5 @@ all need to be considered for everything we introduce)
+ 
+   * Optional history squashing to reduce commit and intermediate
+     tree objects
++
++  * Make use of <blink> and <marquee> tags
diff --git a/t/solve/0002-rename-with-modifications.patch b/t/solve/0002-rename-with-modifications.patch
new file mode 100644
index 0000000..aa415e0
--- /dev/null
+++ b/t/solve/0002-rename-with-modifications.patch
@@ -0,0 +1,37 @@
+From: POLITICAL CORRECTNESS EXPERT <BOFH@YHBT.net>
+To: meta@public-inbox.org
+Subject: [PATCH] POLITICALLY CORRECT FILE NAMING
+Date: Mon, 1 Apr 2019 08:15:20 +0000
+Message-Id: <20190401081523.16213-2-BOFH@YHBT.net>
+
+HACKING MIGHT GET US REPORTED TO EFF-BEE-EYE
+AND USE MARKDOWN CUZ MOAR FLAVORS == BETTER
+---
+ HACKING => CONTRIBUTING.md | 6 +++---
+ 1 file changed, 3 insertions(+), 3 deletions(-)
+ rename HACKING => CONTRIBUTING.md (94%)
+
+diff --git a/HACKING b/CONTRIBUTING.md
+similarity index 94%
+rename from HACKING
+rename to CONTRIBUTING.md
+index 3435775..0a92431 100644
+--- a/HACKING
++++ b/CONTRIBUTING.md
+@@ -1,5 +1,5 @@
+-hacking public-inbox
+---------------------
++contributing to public-inbox
++----------------------------
+ 
+ Send all patches and "git request-pull"-formatted emails to our
+ self-hosting inbox at meta@public-inbox.org
+@@ -15,7 +15,7 @@ Please consider our goals in mind:
+ 	Decentralization, Accessibility, Compatibility, Performance
+ 
+ These goals apply to everyone: users viewing over the web or NNTP,
+-sysadmins running public-inbox, and other hackers working public-inbox.
++sysadmins running public-inbox, and other contributors working public-inbox.
+ 
+ We will reject any feature which advocates or contributes to any
+ particular instance of a public-inbox becoming a single point of failure.
diff --git a/t/solver_git.t b/t/solver_git.t
new file mode 100644
index 0000000..fe322ea
--- /dev/null
+++ b/t/solver_git.t
@@ -0,0 +1,91 @@
+# Copyright (C) 2019 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+use strict;
+use warnings;
+use Test::More;
+use File::Temp qw(tempdir);
+use Cwd qw(abs_path);
+require './t/common.perl';
+require_git(2.6);
+
+my @mods = qw(DBD::SQLite Search::Xapian HTTP::Request::Common Plack::Test
+		URI::Escape Plack::Builder);
+foreach my $mod (@mods) {
+	eval "require $mod";
+	plan skip_all => "$mod missing for $0" if $@;
+}
+chomp(my $git_dir = `git rev-parse --git-dir 2>/dev/null`);
+plan skip_all => "$0 must be run from a git working tree" if $?;
+$git_dir = abs_path($git_dir);
+
+use_ok "PublicInbox::$_" for (qw(Inbox V2Writable MIME Git SolverGit));
+
+my $mainrepo = tempdir('pi-solver-XXXXXX', TMPDIR => 1, CLEANUP => 1);
+my $opts = {
+	mainrepo => $mainrepo,
+	name => 'test-v2writable',
+	version => 2,
+	-primary_address => 'test@example.com',
+};
+my $ibx = PublicInbox::Inbox->new($opts);
+my $im = PublicInbox::V2Writable->new($ibx, 1);
+$im->{parallel} = 0;
+
+sub deliver_patch ($) {
+	open my $fh, '<', $_[0] or die "open: $!";
+	my $mime = PublicInbox::MIME->new(do { local $/; <$fh> });
+	$im->add($mime);
+	$im->done;
+}
+
+deliver_patch('t/solve/0001-simple-mod.patch');
+
+my $gits = [ PublicInbox::Git->new($git_dir) ];
+my $solver = PublicInbox::SolverGit->new($gits, [ $ibx ]);
+open my $log, '+>>', "$mainrepo/solve.log" or die "open: $!";
+my $res = $solver->solve($log, '69df7d5', {});
+ok($res, 'solved a blob!');
+my $wt_git = $res->[0];
+is(ref($wt_git), 'PublicInbox::Git', 'got a git object for the blob');
+my $expect = '69df7d565d49fbaaeb0a067910f03dc22cd52bd0';
+is($res->[1], $expect, 'resolved blob to unabbreviated identifier');
+is($res->[2], 'blob', 'type specified');
+is($res->[3], 4405, 'size returned');
+
+is(ref($wt_git->cat_file($res->[1])), 'SCALAR', 'wt cat-file works');
+is_deeply([$expect, 'blob', 4405],
+	  [$wt_git->check($res->[1])], 'wt check works');
+
+if (0) { # TODO: check this?
+	seek($log, 0, 0);
+	my $z = do { local $/; <$log> };
+	diag $z;
+}
+
+$res = undef;
+my $wt_git_dir = $wt_git->{git_dir};
+$wt_git = undef;
+ok(!-d $wt_git_dir, 'no references to WT held');
+
+$res = $solver->solve($log, '0'x40, {});
+is($res, undef, 'no error on z40');
+
+my $git_v2_20_1_tag = '7a95a1cd084cb665c5c2586a415e42df0213af74';
+$res = $solver->solve($log, $git_v2_20_1_tag, {});
+is($res, undef, 'no error on a tag not in our repo');
+
+deliver_patch('t/solve/0002-rename-with-modifications.patch');
+$res = $solver->solve($log, '0a92431', {});
+ok($res, 'resolved without hints');
+
+my $hints = {
+	oid_a => '3435775',
+	path_a => 'HACKING',
+	path_b => 'CONTRIBUTING'
+};
+my $hinted = $solver->solve($log, '0a92431', $hints);
+# don't compare ::Git objects:
+shift @$res; shift @$hinted;
+is_deeply($res, $hinted, 'hints work (or did not hurt :P');
+
+done_testing();
-- 
EW