git/git-archimport.perl

#!/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;

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 $file = readdir(DIR)) {
	# skip non-interesting-files
	next unless -f "$git_dir/archimport/tags/$file";
	next if     $file =~ m/--base-0$/; # don't care for base-0
	my $sha = ptag($file);
	chomp $sha;
	# reconvert the 3rd '--' sequence from the end
	# into a slash
	# $file = reverse $file;
	# $file =~ s!^(.+?--.+?--.+?--.+?)--(.+)$!$1/$2!;
	# $file = reverse $file;
	$rptags{$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 $commitid;
    close HEAD;
    unlink ("$git_dir/HEAD");
    symlink("refs/heads/$ps->{branch}","$git_dir/HEAD");

    # 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) = @_;
    $tag =~ s|/|--|g; 
    $tag = shell_quote($tag);
    
    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) = @_;
    $tag =~ s|/|--|g; 
    $tag = shell_quote($tag);
    
    unless (-d "$git_dir/archimport/tags") {
        mkpath("$git_dir/archimport/tags");
    }

    if ($commit) {              # write
        open(C,">$git_dir/archimport/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";
	$rptags{$commit} = $tag 
	    unless $tag =~ m/--base-0$/;
    } else {                    # read
        # if the tag isn't there, return 0
        unless ( -s "$git_dir/archimport/tags/$tag") {
            return 0;
        }
        open(C,"<$git_dir/archimport/tags/$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";
	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}`;
	die "Cannot find merge base for $branch and $ps->{branch}" if $?;
	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";
    # the keys in %rptag  are slightly munged; unmunge
    # reconvert the 3rd '--' sequence from the end
    # into a slash
    $name = reverse $name;
    $name =~ s!^(.+?--.+?--.+?--.+?)--(.+)$!$1/$2!;
    $name = reverse $name;
    my $ps   = $psets{$name} 
	|| (print Dumper(sort keys %psets)) && die "Cannot find patchset for $name";
    return $ps;
}