summaryrefslogtreecommitdiff
path: root/git-archimport.perl
blob: d8e6f4e4486223651568532fa628840d5a70254d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
#!/usr/bin/perl -w
#
# This tool is copyright (c) 2005, Martin Langhoff.
# It is released under the Gnu Public License, version 2.
#
# The basic idea is to walk the output of tla abrowse, 
# fetch the changesets and apply them. 
#

=head1 Invocation

    git-archimport [ -h ] [ -v ] [ -T ] [ -t tempdir ] <archive>/<branch> [ <archive>/<branch> ]

Imports a project from one or more Arch repositories. It will follow branches
and repositories within the namespaces defined by the <archive/branch>
parameters suppplied. If it cannot find the remote branch a merge comes from
it will just import it as a regular commit. If it can find it, it will mark it 
as a merge whenever possible.

See man (1) git-archimport for more details.

=head1 TODO

 - create tag objects instead of ref tags
 - audit shell-escaping of filenames
 - hide our private tags somewhere smarter
 - find a way to make "cat *patches | patch" safe even when patchfiles are missing newlines  

=head1 Devel tricks

Add print in front of the shell commands invoked via backticks. 

=cut

use strict;
use warnings;
use Getopt::Std;
use File::Spec;
use File::Temp qw(tempfile tempdir);
use File::Path qw(mkpath);
use File::Basename qw(basename dirname);
use String::ShellQuote;
use Time::Local;
use IO::Socket;
use IO::Pipe;
use POSIX qw(strftime dup2);
use Data::Dumper qw/ Dumper /;
use IPC::Open2;

$SIG{'PIPE'}="IGNORE";
$ENV{'TZ'}="UTC";

my $git_dir = $ENV{"GIT_DIR"} || ".git";
$ENV{"GIT_DIR"} = $git_dir;
my $ptag_dir = "$git_dir/archimport/tags";

our($opt_h,$opt_v, $opt_T,
    $opt_C,$opt_t);

sub usage() {
    print STDERR <<END;
Usage: ${\basename $0}     # fetch/update GIT from Arch
       [ -h ] [ -v ] [ -T ] [ -t tempdir ] 
       repository/arch-branch [ repository/arch-branch] ...
END
    exit(1);
}

getopts("Thvt:") or usage();
usage if $opt_h;

@ARGV >= 1 or usage();
my @arch_roots = @ARGV;

my ($tmpdir, $tmpdirname) = tempdir('git-archimport-XXXXXX', TMPDIR => 1, CLEANUP => 1);
my $tmp = $opt_t || 1;
$tmp = tempdir('git-archimport-XXXXXX', TMPDIR => 1, CLEANUP => 1);
$opt_v && print "+ Using $tmp as temporary directory\n";

my @psets  = ();                # the collection
my %psets  = ();                # the collection, by name

my %rptags = ();                # my reverse private tags
                                # to map a SHA1 to a commitid

foreach my $root (@arch_roots) {
    my ($arepo, $abranch) = split(m!/!, $root);
    open ABROWSE, "tla abrowse -f -A $arepo --desc --merges $abranch |" 
        or die "Problems with tla abrowse: $!";
    
    my %ps        = ();         # the current one
    my $mode      = '';
    my $lastseen  = '';
    
    while (<ABROWSE>) {
        chomp;
        
        # first record padded w 8 spaces
        if (s/^\s{8}\b//) {
            
            # store the record we just captured
            if (%ps) {
                my %temp = %ps; # break references
                push (@psets, \%temp);
		$psets{$temp{id}} = \%temp;
                %ps = ();
            }
            
            my ($id, $type) = split(m/\s{3}/, $_);
            $ps{id}   = $id;
            $ps{repo} = $arepo;

            # deal with types
            if ($type =~ m/^\(simple changeset\)/) {
                $ps{type} = 's';
            } elsif ($type eq '(initial import)') {
                $ps{type} = 'i';
            } elsif ($type =~ m/^\(tag revision of (.+)\)/) {
                $ps{type} = 't';
                $ps{tag}  = $1;
            } else { 
                warn "Unknown type $type";
            }
            $lastseen = 'id';
        }
        
        if (s/^\s{10}//) { 
            # 10 leading spaces or more 
            # indicate commit metadata
            
            # date & author 
            if ($lastseen eq 'id' && m/^\d{4}-\d{2}-\d{2}/) {
                
                my ($date, $authoremail) = split(m/\s{2,}/, $_);
                $ps{date}   = $date;
                $ps{date}   =~ s/\bGMT$//; # strip off trailign GMT
                if ($ps{date} =~ m/\b\w+$/) {
                    warn 'Arch dates not in GMT?! - imported dates will be wrong';
                }
            
                $authoremail =~ m/^(.+)\s(\S+)$/;
                $ps{author} = $1;
                $ps{email}  = $2;
            
                $lastseen = 'date';
            
            } elsif ($lastseen eq 'date') {
                # the only hint is position
                # subject is after date
                $ps{subj} = $_;
                $lastseen = 'subj';
            
            } elsif ($lastseen eq 'subj' && $_ eq 'merges in:') {
                $ps{merges} = [];
                $lastseen = 'merges';
            
            } elsif ($lastseen eq 'merges' && s/^\s{2}//) {
                push (@{$ps{merges}}, $_);
            } else {
                warn 'more metadata after merges!?';
            }
            
        }
    }

    if (%ps) {
        my %temp = %ps;         # break references
        push (@psets, \%temp);  
	$psets{ $temp{id} } = \%temp;
        %ps = ();
    }    
    close ABROWSE;
}                               # end foreach $root

## Order patches by time
@psets = sort {$a->{date}.$b->{id} cmp $b->{date}.$b->{id}} @psets;

#print Dumper \@psets;

##
## TODO cleanup irrelevant patches
##      and put an initial import
##      or a full tag
my $import = 0;
unless (-d $git_dir) { # initial import
    if ($psets[0]{type} eq 'i' || $psets[0]{type} eq 't') {
        print "Starting import from $psets[0]{id}\n";
	`git-init-db`;
	die $! if $?;
	$import = 1;
    } else {
        die "Need to start from an import or a tag -- cannot use $psets[0]{id}";
    }
} else {    # progressing an import
    # load the rptags
    opendir(DIR, "$git_dir/archimport/tags")
	|| die "can't opendir: $!";
    while (my $file = readdir(DIR)) {
        # skip non-interesting-files
        next unless -f "$ptag_dir/$file";
   
        # convert first '--' to '/' from old git-archimport to use
        # as an archivename/c--b--v private tag
        if ($file !~ m!,!) {
            my $oldfile = $file;
            $file =~ s!--!,!;
            print STDERR "converting old tag $oldfile to $file\n";
            rename("$ptag_dir/$oldfile", "$ptag_dir/$file") or die $!;
        }
	my $sha = ptag($file);
	chomp $sha;
	$rptags{$sha} = $file;
    }
    closedir DIR;
}

# process patchsets
foreach my $ps (@psets) {

    $ps->{branch} =  branchname($ps->{id});

    #
    # ensure we have a clean state 
    # 
    if (`git diff-files`) {
        die "Unclean tree when about to process $ps->{id} " .
            " - did we fail to commit cleanly before?";
    }
    die $! if $?;

    #
    # skip commits already in repo
    #
    if (ptag($ps->{id})) {
      $opt_v && print " * Skipping already imported: $ps->{id}\n";
      next;
    }

    print " * Starting to work on $ps->{id}\n";

    # 
    # create the branch if needed
    #
    if ($ps->{type} eq 'i' && !$import) {
        die "Should not have more than one 'Initial import' per GIT import: $ps->{id}";
    }

    unless ($import) { # skip for import
        if ( -e "$git_dir/refs/heads/$ps->{branch}") {
            # we know about this branch
            `git checkout    $ps->{branch}`;
        } else {
            # new branch! we need to verify a few things
            die "Branch on a non-tag!" unless $ps->{type} eq 't';
            my $branchpoint = ptag($ps->{tag});
            die "Tagging from unknown id unsupported: $ps->{tag}" 
                unless $branchpoint;
            
            # find where we are supposed to branch from
            `git checkout -b $ps->{branch} $branchpoint`;

            # If we trust Arch with the fact that this is just 
            # a tag, and it does not affect the state of the tree
            # then we just tag and move on
            tag($ps->{id}, $branchpoint);
            ptag($ps->{id}, $branchpoint);
            print " * Tagged $ps->{id} at $branchpoint\n";
            next;
        } 
        die $! if $?;
    } 

    #
    # Apply the import/changeset/merge into the working tree
    # 
    if ($ps->{type} eq 'i' || $ps->{type} eq 't') {
        apply_import($ps) or die $!;
        $import=0;
    } elsif ($ps->{type} eq 's') {
        apply_cset($ps);
    }

    #
    # prepare update git's index, based on what arch knows
    # about the pset, resolve parents, etc
    #
    my $tree;
    
    my $commitlog = `tla cat-archive-log -A $ps->{repo} $ps->{id}`; 
    die "Error in cat-archive-log: $!" if $?;
        
    # parselog will git-add/rm files
    # and generally prepare things for the commit
    # NOTE: parselog will shell-quote filenames! 
    my ($sum, $msg, $add, $del, $mod, $ren) = parselog($commitlog);
    my $logmessage = "$sum\n$msg";


    # imports don't give us good info
    # on added files. Shame on them
    if ($ps->{type} eq 'i' || $ps->{type} eq 't') { 
        `find . -type f -print0 | grep -zv '^./$git_dir' | xargs -0 -l100 git-update-index --add`;
        `git-ls-files --deleted -z | xargs --no-run-if-empty -0 -l100 git-update-index --remove`;
    }

    if (@$add) {
        while (@$add) {
            my @slice = splice(@$add, 0, 100);
            my $slice = join(' ', @slice);          
            `git-update-index --add $slice`;
            die "Error in git-update-index --add: $!" if $?;
        }
    }
    if (@$del) {
        foreach my $file (@$del) {
            unlink $file or die "Problems deleting $file : $!";
        }
        while (@$del) {
            my @slice = splice(@$del, 0, 100);
            my $slice = join(' ', @slice);
            `git-update-index --remove $slice`;
            die "Error in git-update-index --remove: $!" if $?;
        }
    }
    if (@$ren) {                # renamed
        if (@$ren % 2) {
            die "Odd number of entries in rename!?";
        }
        ;
        while (@$ren) {
            my $from = pop @$ren;
            my $to   = pop @$ren;           

            unless (-d dirname($to)) {
                mkpath(dirname($to)); # will die on err
            }
            #print "moving $from $to";
            `mv $from $to`;
            die "Error renaming $from $to : $!" if $?;
            `git-update-index --remove $from`;
            die "Error in git-update-index --remove: $!" if $?;
            `git-update-index --add $to`;
            die "Error in git-update-index --add: $!" if $?;
        }

    }
    if (@$mod) {                # must be _after_ renames
        while (@$mod) {
            my @slice = splice(@$mod, 0, 100);
            my $slice = join(' ', @slice);
            `git-update-index $slice`;
            die "Error in git-update-index: $!" if $?;
        }
    }

    # warn "errors when running git-update-index! $!";
    $tree = `git-write-tree`;
    die "cannot write tree $!" if $?;
    chomp $tree;
        
    
    #
    # Who's your daddy?
    #
    my @par;
    if ( -e "$git_dir/refs/heads/$ps->{branch}") {
        if (open HEAD, "<$git_dir/refs/heads/$ps->{branch}") {
            my $p = <HEAD>;
            close HEAD;
            chomp $p;
            push @par, '-p', $p;
        } else { 
            if ($ps->{type} eq 's') {
                warn "Could not find the right head for the branch $ps->{branch}";
            }
        }
    }
    
    if ($ps->{merges}) {
        push @par, find_parents($ps);
    }
    my $par = join (' ', @par);

    #    
    # Commit, tag and clean state
    #
    $ENV{TZ}                  = 'GMT';
    $ENV{GIT_AUTHOR_NAME}     = $ps->{author};
    $ENV{GIT_AUTHOR_EMAIL}    = $ps->{email};
    $ENV{GIT_AUTHOR_DATE}     = $ps->{date};
    $ENV{GIT_COMMITTER_NAME}  = $ps->{author};
    $ENV{GIT_COMMITTER_EMAIL} = $ps->{email};
    $ENV{GIT_COMMITTER_DATE}  = $ps->{date};

    my ($pid, $commit_rh, $commit_wh);
    $commit_rh = 'commit_rh';
    $commit_wh = 'commit_wh';
    
    $pid = open2(*READER, *WRITER, "git-commit-tree $tree $par") 
        or die $!;
    print WRITER $logmessage;   # write
    close WRITER;
    my $commitid = <READER>;    # read
    chomp $commitid;
    close READER;
    waitpid $pid,0;             # close;

    if (length $commitid != 40) {
        die "Something went wrong with the commit! $! $commitid";
    }
    #
    # Update the branch
    # 
    open  HEAD, ">$git_dir/refs/heads/$ps->{branch}";
    print HEAD $commitid;
    close HEAD;
    system('git-update-ref', 'HEAD', "$ps->{branch}");

    # tag accordingly
    ptag($ps->{id}, $commitid); # private tag
    if ($opt_T || $ps->{type} eq 't' || $ps->{type} eq 'i') {
        tag($ps->{id}, $commitid);
    }
    print " * Committed $ps->{id}\n";
    print "   + tree   $tree\n";
    print "   + commit $commitid\n";
    $opt_v && print "   + commit date is  $ps->{date} \n";
    $opt_v && print "   + parents:  $par \n";
}

sub branchname {
    my $id = shift;
    $id =~ s#^.+?/##;
    my @parts = split(m/--/, $id);
    return join('--', @parts[0..1]);
}

sub apply_import {
    my $ps = shift;
    my $bname = branchname($ps->{id});

    `mkdir -p $tmp`;

    `tla get -s --no-pristine -A $ps->{repo} $ps->{id} $tmp/import`;
    die "Cannot get import: $!" if $?;    
    `rsync -v --archive --delete --exclude '$git_dir' --exclude '.arch-ids' --exclude '{arch}' $tmp/import/* ./`;
    die "Cannot rsync import:$!" if $?;
    
    `rm -fr $tmp/import`;
    die "Cannot remove tempdir: $!" if $?;
    

    return 1;
}

sub apply_cset {
    my $ps = shift;

    `mkdir -p $tmp`;

    # get the changeset
    `tla get-changeset  -A $ps->{repo} $ps->{id} $tmp/changeset`;
    die "Cannot get changeset: $!" if $?;
    
    # apply patches
    if (`find $tmp/changeset/patches -type f -name '*.patch'`) {
        # this can be sped up considerably by doing
        #    (find | xargs cat) | patch
        # but that cna get mucked up by patches
        # with missing trailing newlines or the standard 
        # 'missing newline' flag in the patch - possibly
        # produced with an old/buggy diff.
        # slow and safe, we invoke patch once per patchfile
        `find $tmp/changeset/patches -type f -name '*.patch' -print0 | grep -zv '{arch}' | xargs -iFILE -0 --no-run-if-empty patch -p1 --forward -iFILE`;
        die "Problem applying patches! $!" if $?;
    }

    # apply changed binary files
    if (my @modified = `find $tmp/changeset/patches -type f -name '*.modified'`) {
        foreach my $mod (@modified) {
            chomp $mod;
            my $orig = $mod;
            $orig =~ s/\.modified$//; # lazy
            $orig =~ s!^\Q$tmp\E/changeset/patches/!!;
            #print "rsync -p '$mod' '$orig'";
            `rsync -p $mod ./$orig`;
            die "Problem applying binary changes! $!" if $?;
        }
    }

    # bring in new files
    `rsync --archive --exclude '$git_dir' --exclude '.arch-ids' --exclude '{arch}' $tmp/changeset/new-files-archive/* ./`;

    # deleted files are hinted from the commitlog processing

    `rm -fr $tmp/changeset`;
}


# =for reference
# A log entry looks like 
# Revision: moodle-org--moodle--1.3.3--patch-15
# Archive: arch-eduforge@catalyst.net.nz--2004
# Creator: Penny Leach <penny@catalyst.net.nz>
# Date: Wed May 25 14:15:34 NZST 2005
# Standard-date: 2005-05-25 02:15:34 GMT
# New-files: lang/de/.arch-ids/block_glossary_random.php.id
#     lang/de/.arch-ids/block_html.php.id
# New-directories: lang/de/help/questionnaire
#     lang/de/help/questionnaire/.arch-ids
# Renamed-files: .arch-ids/db_sears.sql.id db/.arch-ids/db_sears.sql.id
#    db_sears.sql db/db_sears.sql
# Removed-files: lang/be/docs/.arch-ids/release.html.id
#     lang/be/docs/.arch-ids/releaseold.html.id
# Modified-files: admin/cron.php admin/delete.php
#     admin/editor.html backup/lib.php backup/restore.php
# New-patches: arch-eduforge@catalyst.net.nz--2004/moodle-org--moodle--1.3.3--patch-15
# Summary: Updating to latest from MOODLE_14_STABLE (1.4.5+)
# Keywords:
#
# Updating yadda tadda tadda madda
sub parselog {
    my $log = shift;
    #print $log;

    my (@add, @del, @mod, @ren, @kw, $sum, $msg );

    if ($log =~ m/(?:\n|^)New-files:(.*?)(?=\n\w)/s ) {
        my $files = $1;
        @add = split(m/\s+/s, $files);
    }
       
    if ($log =~ m/(?:\n|^)Removed-files:(.*?)(?=\n\w)/s ) {
        my $files = $1;
        @del = split(m/\s+/s, $files);
    }
    
    if ($log =~ m/(?:\n|^)Modified-files:(.*?)(?=\n\w)/s ) {
        my $files = $1;
        @mod = split(m/\s+/s, $files);
    }
    
    if ($log =~ m/(?:\n|^)Renamed-files:(.*?)(?=\n\w)/s ) {
        my $files = $1;
        @ren = split(m/\s+/s, $files);
    }

    $sum ='';
    if ($log =~ m/^Summary:(.+?)$/m ) {
        $sum = $1;
        $sum =~ s/^\s+//;
        $sum =~ s/\s+$//;
    }

    $msg = '';
    if ($log =~ m/\n\n(.+)$/s) {
        $msg = $1;
        $msg =~ s/^\s+//;
        $msg =~ s/\s+$//;
    }


    # cleanup the arrays
    foreach my $ref ( (\@add, \@del, \@mod, \@ren) ) {
        my @tmp = ();
        while (my $t = pop @$ref) {
            next unless length ($t);
            next if $t =~ m!\{arch\}/!;
            next if $t =~ m!\.arch-ids/!;
            next if $t =~ m!\.arch-inventory$!;
           # tla cat-archive-log will give us filenames with spaces as file\(sp)name - why?
           # we can assume that any filename with \ indicates some pika escaping that we want to get rid of.
           if  ($t =~ /\\/ ){
               $t = `tla escape --unescaped '$t'`;
           }
            push (@tmp, shell_quote($t));
        }
        @$ref = @tmp;
    }
    
    #print Dumper [$sum, $msg, \@add, \@del, \@mod, \@ren]; 
    return       ($sum, $msg, \@add, \@del, \@mod, \@ren); 
}

# write/read a tag
sub tag {
    my ($tag, $commit) = @_;
 
    # don't use subdirs for tags yet, it could screw up other porcelains
    $tag =~ s|/|,|;
    
    if ($commit) {
        open(C,">","$git_dir/refs/tags/$tag")
            or die "Cannot create tag $tag: $!\n";
        print C "$commit\n"
            or die "Cannot write tag $tag: $!\n";
        close(C)
            or die "Cannot write tag $tag: $!\n";
        print " * Created tag '$tag' on '$commit'\n" if $opt_v;
    } else {                    # read
        open(C,"<","$git_dir/refs/tags/$tag")
            or die "Cannot read tag $tag: $!\n";
        $commit = <C>;
        chomp $commit;
        die "Error reading tag $tag: $!\n" unless length $commit == 40;
        close(C)
            or die "Cannot read tag $tag: $!\n";
        return $commit;
    }
}

# write/read a private tag
# reads fail softly if the tag isn't there
sub ptag {
    my ($tag, $commit) = @_;

    # don't use subdirs for tags yet, it could screw up other porcelains
    $tag =~ s|/|,|g; 
    
    my $tag_file = "$ptag_dir/$tag";
    my $tag_branch_dir = dirname($tag_file);
    mkpath($tag_branch_dir) unless (-d $tag_branch_dir);

    if ($commit) {              # write
        open(C,">",$tag_file)
            or die "Cannot create tag $tag: $!\n";
        print C "$commit\n"
            or die "Cannot write tag $tag: $!\n";
        close(C)
            or die "Cannot write tag $tag: $!\n";
	$rptags{$commit} = $tag 
	    unless $tag =~ m/--base-0$/;
    } else {                    # read
        # if the tag isn't there, return 0
        unless ( -s $tag_file) {
            return 0;
        }
        open(C,"<",$tag_file)
            or die "Cannot read tag $tag: $!\n";
        $commit = <C>;
        chomp $commit;
        die "Error reading tag $tag: $!\n" unless length $commit == 40;
        close(C)
            or die "Cannot read tag $tag: $!\n";
	unless (defined $rptags{$commit}) {
	    $rptags{$commit} = $tag;
	}
        return $commit;
    }
}

sub find_parents {
    #
    # Identify what branches are merging into me
    # and whether we are fully merged
    # git-merge-base <headsha> <headsha> should tell
    # me what the base of the merge should be 
    #
    my $ps = shift;

    my %branches; # holds an arrayref per branch
                  # the arrayref contains a list of
                  # merged patches between the base
                  # of the merge and the current head

    my @parents;  # parents found for this commit

    # simple loop to split the merges
    # per branch
    foreach my $merge (@{$ps->{merges}}) {
	my $branch = branchname($merge);
	unless (defined $branches{$branch} ){
	    $branches{$branch} = [];
	}
	push @{$branches{$branch}}, $merge;
    }

    #
    # foreach branch find a merge base and walk it to the 
    # head where we are, collecting the merged patchsets that
    # Arch has recorded. Keep that in @have
    # Compare that with the commits on the other branch
    # between merge-base and the tip of the branch (@need)
    # and see if we have a series of consecutive patches
    # starting from the merge base. The tip of the series
    # of consecutive patches merged is our new parent for 
    # that branch.
    #
    foreach my $branch (keys %branches) {

	# check that we actually know about the branch
	next unless -e "$git_dir/refs/heads/$branch";

	my $mergebase = `git-merge-base $branch $ps->{branch}`;
 	if ($?) { 
 	    # Don't die here, Arch supports one-way cherry-picking
 	    # between branches with no common base (or any relationship
 	    # at all beforehand)
 	    warn "Cannot find merge base for $branch and $ps->{branch}";
 	    next;
 	}
	chomp $mergebase;

	# now walk up to the mergepoint collecting what patches we have
	my $branchtip = git_rev_parse($ps->{branch});
	my @ancestors = `git-rev-list --merge-order $branchtip ^$mergebase`;
	my %have; # collected merges this branch has
	foreach my $merge (@{$ps->{merges}}) {
	    $have{$merge} = 1;
	}
	my %ancestorshave;
	foreach my $par (@ancestors) {
	    $par = commitid2pset($par);
	    if (defined $par->{merges}) {
		foreach my $merge (@{$par->{merges}}) {
		    $ancestorshave{$merge}=1;
		}
	    }
	}
	# print "++++ Merges in $ps->{id} are....\n";
	# my @have = sort keys %have;	print Dumper(\@have);

	# merge what we have with what ancestors have
	%have = (%have, %ancestorshave);

	# see what the remote branch has - these are the merges we 
	# will want to have in a consecutive series from the mergebase
	my $otherbranchtip = git_rev_parse($branch);
	my @needraw = `git-rev-list --merge-order $otherbranchtip ^$mergebase`;
	my @need;
	foreach my $needps (@needraw) { 	# get the psets
	    $needps = commitid2pset($needps);
	    # git-rev-list will also
	    # list commits merged in via earlier 
	    # merges. we are only interested in commits
	    # from the branch we're looking at
	    if ($branch eq $needps->{branch}) {
		push @need, $needps->{id};
	    }
	}

	# print "++++ Merges from $branch we want are....\n";
	# print Dumper(\@need);

	my $newparent;
	while (my $needed_commit = pop @need) {
	    if ($have{$needed_commit}) {
		$newparent = $needed_commit;
	    } else {
		last; # break out of the while
	    }
	}
	if ($newparent) {
	    push @parents, $newparent;
	}


    } # end foreach branch

    # prune redundant parents
    my %parents;
    foreach my $p (@parents) {
	$parents{$p} = 1;
    }
    foreach my $p (@parents) {
	next unless exists $psets{$p}{merges};
	next unless ref    $psets{$p}{merges};
	my @merges = @{$psets{$p}{merges}};
	foreach my $merge (@merges) {
	    if ($parents{$merge}) { 
		delete $parents{$merge};
	    }
	}
    }
    @parents = keys %parents;
    @parents = map { " -p " . ptag($_) } @parents;
    return @parents;
}

sub git_rev_parse {
    my $name = shift;
    my $val  = `git-rev-parse $name`;
    die "Error: git-rev-parse $name" if $?;
    chomp $val;
    return $val;
}

# resolve a SHA1 to a known patchset
sub commitid2pset {
    my $commitid = shift;
    chomp $commitid;
    my $name = $rptags{$commitid} 
	|| die "Cannot find reverse tag mapping for $commitid";
    $name =~ s|,|/|;
    my $ps   = $psets{$name} 
	|| (print Dumper(sort keys %psets)) && die "Cannot find patchset for $name";
    return $ps;
}