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✏️ Editing: dh_assistant

#!/usr/bin/perl

=head1 NAME

dh_assistant - tool for supporting debhelper tools and provide introspection

=cut

use strict;
use warnings;
use Debian::Debhelper::Dh_Lib;
use JSON::PP ();

=head1 SYNOPSIS

B<dh_assistant> B<I<command>> [S<I<additional options>>]

=head1 DESCRIPTION

B<dh_assistant> is a debhelper program that provides introspection into the
debhelper stack to assist third-party tools (e.g. linters) or third-party
debhelper implementations not using the debhelper script API (e.g., because
they are not written in Perl).

=head1 COMMANDS

The B<dh_assistant> supports the following commands:

=head2 active-compat-level (JSON)

B<Synopsis>: B<dh_assistant> B<active-compat-levels>

Outputs information about which compat level the package is using.

For packages without valid debhelper compatibility information (whether missing, ambiguous,
not supported or simply invalid), this command operates on a "best effort" basis and may abort
when error instead of providing data.

The returned JSON dictionary contains the following key-value pairs:

=over 4

=item active-compat-level

The compat level that debhelper will be using.  This is the same as B<DH_COMPAT> when present
or else B<declared-compat-level>.  This can be B<null> when no compat level can be detected.

=item declared-compat-level

The compat level that the package declared as its default compat level.  This can be B<null>
if the package does not declare any compat level at all.

=item declared-compat-level-source

Defines how the compat level was declared.  This is null (for the same reason as
B<declared-compat-level>) or one of:

=over 4

=item debian/compat

The compatibility level was declared in the first line F<debian/compat> file.

=item Build-Depends: debhelper-compat (= <C>)

The compatibility was declared in the F<debian/control> via a build dependency on the
B<< debhelper-compat (= <C>) >> package in the B<Build-Depends> field.  In the output,
the B<C> is replaced by the actual compatibility level.  A full example value would be:

Build-Depends: debhelper-compat (= 13)

=back

=head2 supported-compat-levels (JSON, CRFA)

B<Synopsis>: B<dh_assistant> B<supported-compat-levels>

Outputs information about which compat levels, this build of debhelper knows
about.

This command accepts no options or arguments.

=head2 which-build-system (JSON)

B<Synopsis>: B<dh_assistant> B<which-build-system> [S<I<build step>>] [S<I<build system options>>]

Output information about which build system would be used for a particular build step.  The build step
must be one of B<configure>, B<build>, B<test>, B<install> or B<clean> and must be the first argument
after B<which-build-system> when provided.  If omitted, it defaults to B<configure> as it is the
most reliable step to use auto-detection on in a clean source directory.  Note that build steps do not
always agree when using auto-detection - particularly if the B<configure> step has not been run.

Additionally, the B<clean> step can also provide "surprising" results for builds that rely on
a separate build directory.  In such cases, debhelper will return the first build system that
uses a separate build directory rather than the one build system that B<configure> would detect.
This is generally a cosmetic issue as both build systems are all basically a glorified
B<rm -fr builddir> and more precise detection is functionally irrelevant as far as debhelper is
concerned.

The option accepts all debhelper build system arguments - i.e., options you can pass to all of
the B<dh_auto_*> commands plus (for the B<install> step) the B<--destdir> option.  These options
affect the output and auto-detection in various ways.  Passing B<-S> or B<--buildsystem>
overrides the auto-detection (as it does for B<dh_auto_*>) but it still provides introspection
into the chosen build system.

Things that are useful to know about the output:

=over 4

=item *

The key B<build-system> is the build system that would be used by debhelper for the given
step (with the given options, debhelper compat level, environment variables and the given
working directory).  When B<-S> and B<--buildsystem> are omitted, this is the result of
debhelper's auto-detection logic.

The value is valid as a parameter for the B<--buildsystem> option.

The special value B<none> is used to denote that no build system would be used.  This value
is not present in B<--list> parameter for the B<dh_auto_*> commands, but since debhelper/12.9
the value is accepted for the B<--buildsystem> option.

Note that auto-detection is subject to limitations in regards to third-party build systems.
While debhelper I<does> support auto-detecting some third-party build systems, they must be
installed for the detection to work.  If they are not installed, the detection logic silently
skips that build system (often resulting in B<build-system> being B<none> in the output).

=item *

The B<build-directory> and B<buildpath> values serve different but related purposes.  The
B<build-directory> generally mirrors the B<--builddirectory> option where as B<buildpath>
is the output directory that debhelper will use.  Therefore the former will often be null
when B<--builddirectory> has not been passed while the latter will generally not be null
(except when B<build-system> is B<none>).

=item *

The B<dest-directory> (B<--destdir>) is undefined for all build steps except the B<install> build
step (will be output as null or absent).  For the same reason, B<--destdir> should only be
passed for B<install> build step.

Note that if not specified, this value is currently null by default.

=item *

The B<parallel> value is subject to B<DEB_BUILD_OPTIONS>.  Notably, if that does not include
the B<parallel> keyword, then B<parallel> field in the output will always be 1.

=item *

Most fields in the output I<can> be null.  Particular if there is no build system is detected
(or when B<--buildsystem=none>).  Additionally, many of the fields can be null even if there
is a build system if the build system does not use/set/define that variable.

=back

=head2 COMMAND TAGS

Most commands have one or more of the following "tags" associated with them.  Their
meaning is defined here.

=over 4

=item JSON

The command provides JSON output. See L</JSON OUTPUT> for details.

=item CRFA

I<Mnemonic "Can be Run From Anywhere">

Most commands must be run inside a source package root directory (a directory
containing F<debian/control>) because debhelper will need the package metadata
to lookup the information.  Any command with this tag are exempt from this
requirement and is expected to work regardless of where they are run.

=back

=head1 JSON OUTPUT

Most commands uses JSON format as output.  Consumers need to be aware that:

=over 4

=item *

Additional keys may be added at any time.  For backwards compatibility, the absence
of a key should in general be interpreted as null unless another default is documented
or would be "obvious" for that case.

=item *

Many keys can be null/undefined in special cases.  As an example, some information may
be unavailable when this command is run directly from the debhelper source (git repository).

=back

The output will be prettified when stdout is detected as a terminal.  If
you need to pipe the output to a pager/file (etc.) and still want it
prettified, please use an external JSON formatter. An example of this:

dh_assistant supported-compat-levels | python3 -m json.tool | less

=cut

my $JSON_ENCODER = JSON::PP->new->utf8;

# Prettify if we think the user is reading this.
$JSON_ENCODER = $JSON_ENCODER->pretty->space_before(0)->canonical if -t STDOUT;

# We never use the log file for this tool
inhibit_log();

my %COMMANDS = (
    'help'                    => \&_do_help,
    '-h'                      => \&_do_help,
    '--help'                  => \&_do_help,
    'active-compat-level'     => \&active_compat_level,
    'supported-compat-levels' => \&supported_compat_levels,
    'which-build-system'      => \&which_build_system,
);

my ($COMMAND) = shift(@ARGV);
for my $arg (@ARGV) {
    if ($arg eq '--help' or $arg eq '-h') {
        $COMMAND = 'help';
        last;
    }
}

sub _do_help {
    my $me = basename($0);
    print <<"EOF";
${me}: Tool for supporting debhelper tools and provide introspection

Usage: ${me} <command> [... addition arguments or options ...]

The following commands are available:
  help                       Show this help
  active-compat-level        Output information about which compat level is declared/active (JSON)
  supported-compat-levels    Output information about supported compat levels (JSON, CRFA)
  which-build-system         Determine which build system will be used (JSON)

Command tags:

* JSON    The command provides JSON output.
 * CRFA    Command does not need to be run from a package source directory
           (Mnemonic "Can be Run From Anywhere")

Its primary purpose is to provide support for third-party debhelper implementations
not using the debhelper script API or provide introspection for third-party tools
(e.g., linters).  Unless stated otherwise, commands must be run inside a source
package root directory - that is, the directory containing "debian/control".

Most commands use JSON output.  When stdout is a TTY, the JSON will be prettified.
See the manpage if you want formatting in other cases.
EOF
    return;
}

sub _assert_debian_control_exists {
    return if -f 'debian/control';
    require Cwd;
    my $cwd = Cwd::getcwd();
    warning("$cwd does not look like a package source directory (expected $cwd/debian/control to exist and be a file)");
    error("$COMMAND must be run inside a package source directory");
    return;
}

sub _output {
    my ($kvpairs) = @_;
    print $JSON_ENCODER->encode($kvpairs);
    return;
}

sub active_compat_level {
    if (@ARGV) {
        error("$COMMAND: No arguments supported (please remove everything after the command)");
    }
    _assert_debian_control_exists();
    my ($active_compat, $declared_compat, $declared_compat_source) = Debian::Debhelper::Dh_Lib::get_compat_info();
    if (not defined($declared_compat_source)) {
        $declared_compat = undef;
        $active_compat = undef if not exists($ENV{DH_COMPAT});
    }
    my %compat_info = (
        'active-compat-level'          => $active_compat,
        'declared-compat-level'        => $declared_compat,
        'declared-compat-level-source' => $declared_compat_source,
    );
    _output(\%compat_info);
    return;
}

sub supported_compat_levels {
    if (@ARGV) {
        error("$COMMAND: No arguments supported (please remove everything after the command)");
    }
    my %compat_levels = (
        'MIN_COMPAT_LEVEL'                           => Debian::Debhelper::Dh_Lib::MIN_COMPAT_LEVEL,
        'LOWEST_NON_DEPRECATED_COMPAT_LEVEL'         => Debian::Debhelper::Dh_Lib::LOWEST_NON_DEPRECATED_COMPAT_LEVEL,
        'LOWEST_VIRTUAL_DEBHELPER_COMPAT_LEVEL'      => Debian::Debhelper::Dh_Lib::LOWEST_VIRTUAL_DEBHELPER_COMPAT_LEVEL,
        'MAX_COMPAT_LEVEL'                           => Debian::Debhelper::Dh_Lib::MAX_COMPAT_LEVEL,
        'HIGHEST_STABLE_COMPAT_LEVEL'                => Debian::Debhelper::Dh_Lib::HIGHEST_STABLE_COMPAT_LEVEL,
        'MIN_COMPAT_LEVEL_NOT_SCHEDULED_FOR_REMOVAL' => Debian::Debhelper::Dh_Lib::MIN_COMPAT_LEVEL_NOT_SCHEDULED_FOR_REMOVAL,
    );
    _output(\%compat_levels);
    return;
}

sub which_build_system {
    my ($opt_buildsys, $destdir);
    my $first_argv = @ARGV ? $ARGV[0] : '';
    my %options = (
        # Emulate dh_auto_install's --destdir
        "destdir=s" => \$destdir,
    );
    _assert_debian_control_exists();
    # We never want the build system initialization to modify anything (e.g. create "HOME")
    $dh{NO_ACT} = 1;
    require Debian::Debhelper::Dh_Buildsystems;
    Debian::Debhelper::Dh_Buildsystems::buildsystems_init(options => \%options);
    my @non_options = grep { !m/^-/ } @ARGV;
    my $step = @non_options ? $non_options[0] : 'configure';
    if (@non_options && $first_argv =~ m/^-/) {
        error("$COMMAND: If the build step is provided, it must be before any options");
    }
    if (@non_options > 1) {
        error("$COMMAND: At most one positional argument is supported");
    }
    if (defined($destdir) and $step ne 'install') {
        warning("$COMMAND: --destdir is not defined for build step \"$step\". Ignoring option")
    }
    {
        no warnings qw(once);
        $opt_buildsys = $Debian::Debhelper::Dh_Buildsystems::opt_buildsys;
    }
    my $build_system = Debian::Debhelper::Dh_Buildsystems::load_buildsystem($opt_buildsys, $step);
    my %result = (
        'build-system'       => defined($build_system) ? $build_system->NAME : 'none',
        'for-build-step'     => $step,
        'source-directory'   => defined($build_system) ? $build_system->get_sourcedir : undef,
        'build-directory'    => defined($build_system) ? $build_system->get_builddir : undef,
        'dest-directory'     => defined($build_system) ? $destdir : undef,
        'buildpath'          => defined($build_system) ? $build_system->get_buildpath : undef,
        'parallel'           => defined($build_system) ? $build_system->get_parallel : undef,
        'upstream-arguments' => $dh{U_PARAMS},
    );
    _output(\%result);
    return;
}

if (not defined($COMMAND)) {
    error('Usage: ' . basename($0) . ' <command>');
}
my $handler = $COMMANDS{$COMMAND};
if (not defined($handler)) {
    warning("Arguments/options must not be the first argument (except for --help)")
        if $COMMAND =~ m/^-/;
    error("Unknown command: $COMMAND");
}

$handler->();

=head1 SEE ALSO

L<debhelper(7)>

This program is a part of debhelper.

=cut

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