dh_movetousr

#!/usr/bin/perl

=head1 NAME

dh_movetousr - canonicalize location according to merged-/usr

=cut

use strict;
use warnings;
use Config;
use File::Find;
use File::Spec;
use Debian::Debhelper::Dh_Lib;

our $VERSION = DH_BUILTIN_VERSION;

=head1 SYNOPSIS

B<dh_movetousr> [S<I<debhelper options>>] [B<--fail-noop> | B<--warn-noop>]

=head1 DESCRIPTION

B<dh_movetousr> is a B<debhelper> program that canonicalizes paths inside packages according to merged-/usr.
Shipping aliased paths is known to cause problems with B<dpkg>, so this helper moves all affected files to F</usr> regardless of how they were installed.
The compatibility symlinks ensure that converted packages continue to work.
In the process, absolute symbolic links may become relative or vice versa due to Debian policy section 10.5.

Please keep in mind that moving files in this way is known to cause problems.
Known problems have been documented at L<https://people.debian.org/~helmutg/dep17.html>.
For instance, if files have been moved between packages, use of this tool may cause file loss during upgrades (P1).
Most problems can be detected by L<https://salsa.debian.org/helmutg/dumat>, which uses the Debian bug tracking for feedback.
Therefore, it is recommended to upload to B<experimental> when moving files (e.g. using this helper) or restructuring packages that earlier moved files.
A particular problem not being detected is about B<dpkg-statoverride> (P5).
Please review uses of B<dpkg-statoverride> in maintainer scripts and update them as needed.
For these reasons, B<dh_movetousr> is not automatically enabled in e.g. a compatibility level.

While we want to move files to F</usr> in B<trixie> and beyond, we do not want to move them in B<bookworm> and earlier.
This poses challenges to backporting packages, because any such moves have to be reverted during the backport.
A backport of B<debhelper> to B<bookworm> shall include a stub for this helper doing nothing to achieve this goal.
For packages that do not need to be backported (e.g. packages targeting B<forky> and beyond), consider updating locations instead of using this helper.
When the only affected type of file is B<systemd> units, consider using B<dh_installsystemd> or detecting the unit location from C<pkgconf --variable=systemdsystemunitdir systemd> instead of this helper as both will work in backports.

For further information on the state of the transition refer to L<https://wiki.debian.org/UsrMerge>.

B<dh_movetousr> shall be removed from B<debhelper> during B<forky+1> is release cycle.

=head1 OPTIONS

=over 4

=item B<--fail-noop>

Fail if no files were found in aliased locations and therefore no change has
been performed.

=item B<--warn-noop>

Warn if no files were found in aliased locations and therefore no change has
been performed.

=back

=head1 EXAMPLES

  Build-Depends: dh-sequence-movetousr

Enable this tool in a package that uses B<dh>.

=cut

init(options => {
	'fail-noop!' => sub { $dh{NOOP_LEVEL} = 'error'; },
	'warn-noop!' => sub { $dh{NOOP_LEVEL} = 'warning'; },
});

my @merged_directories = (
	qw{bin lib lib64 libo32 libx32 sbin},
);
my $merged_dir_pattern = join('|', @merged_directories);

sub merge_entry {
	my ($package, $rootdir, $location) = @_;
	if (-l "$rootdir/usr/$location") {
		error("cannot move $location to /usr in $package, because it exists there as a symlink");
	} elsif (-l "$rootdir/$location") {
		if (-e "$rootdir/usr/$location") {
			error("cannot move symlink $location to /usr in $package, because it already exists there");
		}
		my $target = readlink("$rootdir/$location");
		my $recreate = 0;  # Whether the link target should be recomputed.
		my @newtarget;  # Represented as split m|/|. Relative to /.
		if ($target !~ m,^/,) {
			# In case the original target is relative, prepend the
			# basename of the link location.
			@newtarget = split(m|/+|, $location);
			pop @newtarget;
		}
		# Append the original target, resolving any '../', './' and
		# double-slashes.
		foreach my $part (split(m|/+|, $target)) {
			if ($part eq '..') {
				# If the link goes past /, recreate.
				$recreate = 1 if (scalar @newtarget <= 1);
				pop @newtarget if (scalar @newtarget > 0);
			} elsif ($part ne '' && $part ne '.') {
				push @newtarget, $part;
			}
		}
		if (grep { $_ eq $newtarget[0] } @merged_directories) {
			# If the link target is aliased, unalias and recreate.
			unshift @newtarget, 'usr';
			$recreate = 1;
		} elsif ($target =~ m,^/, && $newtarget[0] eq 'usr') {
			# If the original link is absolute and now points to
			# /usr, recreate.
			$recreate = 1;
		}
		if ($recreate) {
			make_symlink("usr/$location", join('/', @newtarget), $rootdir);
			rm_files("$rootdir/$location");
		} else {
			rename_path("$rootdir/$location", "$rootdir/usr/$location");
		}
	} elsif (-d "$rootdir/$location") {
		my $did_mkdir = 0;
		if (! -d "$rootdir/usr/$location") {
			if (-e "$rootdir/usr/$location") {
				error("cannot move directory $location to /usr in $package as it exists in /usr as a non-directory");
			} else {
				install_dir("$rootdir/usr/$location");
				$did_mkdir = 1;
			}
		}
		opendir(my $dh, "$rootdir/$location") or
			error("cannot open directory $rootdir/$location: $!");
		while (my $entry = readdir($dh)) {
			next if ($entry eq "." || $entry eq "..");
			merge_entry($package, $rootdir, "$location/$entry");
		}
		closedir($dh);
		if ($did_mkdir) {
			doit("chown", "--reference", "$rootdir/$location", "$rootdir/usr/$location");
			doit("chmod", "--reference", "$rootdir/$location", "$rootdir/usr/$location");
		}
		verbose_print('rmdir ' . escape_shell("$rootdir/$location"))
			if $dh{VERBOSE};
		rmdir("$rootdir/$location") or
			error("rmdir $rootdir/$location failed: $!");
	} elsif (-e "$rootdir/usr/$location") {
		error("cannot move $location to /usr in $package, because it already exists there");
	} else {
		rename_path("$rootdir/$location", "$rootdir/usr/$location");
	}
}

my ($is_noop) = 1;
sub process_packages {
	foreach my $package (@_) {
		my $tmp = tmpdir($package);

		next if ! -d $tmp;

		if (-d "$tmp/usr") {
			# Reconstruct absolute symlinks pointing from /usr into an
			# aliased directory.
			find (
				{
					wanted => sub {
						return unless -l;
						my $target = readlink($_);
						return unless ($target =~ m,^/($merged_dir_pattern)(/|$),);
						s|^\Q$tmp\E||;
						make_symlink("$_", "usr/$target", $tmp);
					},
					no_chdir => 1
				},
				"$tmp/usr"
			);
		}

		foreach my $dir (@merged_directories) {
			if (-d "$tmp/$dir" && ! -l "$tmp/$dir") {
				merge_entry($package, $tmp, $dir);
				$is_noop = 0;
			}
		}
	}
}

if (exists $ENV{'DEB_BUILD_PROFILES'} || ! exists $dh{NOOP_LEVEL}) {
	on_pkgs_in_parallel(\&process_packages);
} else {
	process_packages(@{$dh{DOPACKAGES}});
	if ($is_noop) {
		warning('dh_movetousr did not move any files to /usr');
		if (exists $ENV{DH_INTERNAL_MOVETOUSR_IS_ADDON}) {
			if ($dh{DOARCH} && ! $dh{DOINDEP} && getpackages('indep')) {
				warning('consider moving dh-sequence-movetousr to Build-Depends-Indep');
			} elsif ($dh{DOINDEP} && ! $dh{DOARCH} && getpackages('arch')) {
				warning('consider moving dh-sequence-movetousr to Build-Depends-Arch');
			} else {
				warning('consider dropping dh-sequence-movetousr from Build-Depends');
			}
		} else {
			if ($dh{DOARCH} && ! $dh{DOINDEP} && getpackages('indep')) {
				warning('consider passing -i to dh_movetousr');
			} elsif ($dh{DOINDEP} && ! $dh{DOARCH} && getpackages('arch')) {
				warning('consider passing -a to dh_movetousr');
			} else {
				warning('consider deleting the dh_movetousr invocation');
			}
		}
		if ($dh{NOOP_LEVEL} eq 'error') {
			error('failing as requested');
		}
	}
}

=head1 SEE ALSO

L<debhelper(7)>

This program is a part of debhelper.

=head1 AUTHOR

Helmut Grohne <helmut@subdivi.de>

=cut