path: root/Bugzilla/Install/Util.pm

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
#
# This Source Code Form is "Incompatible With Secondary Licenses", as
# defined by the Mozilla Public License, v. 2.0.

package Bugzilla::Install::Util;

# The difference between this module and Bugzilla::Util is that this
# module may require *only* Bugzilla::Constants and built-in
# perl modules.

use 5.10.1;
use strict;

use Bugzilla::Constants;

use Encode;
use File::Basename;
use File::Spec;
use POSIX qw(setlocale LC_CTYPE);
use Scalar::Util qw(tainted);
use Term::ANSIColor qw(colored);
use PerlIO;

use base qw(Exporter);
our @EXPORT_OK = qw(
    bin_loc
    get_version_and_os
    extension_code_files
    extension_package_directory
    extension_requirement_packages
    extension_template_directory
    extension_web_directory
    indicate_progress
    install_string
    include_languages
    success
    template_include_path
    vers_cmp
    init_console
);

sub bin_loc {
    my ($bin, $path) = @_;
    # This module is not needed most of the time and is a bit slow,
    # so we only load it when calling bin_loc().
    require ExtUtils::MM;

    # If the binary is a full path...
    if ($bin =~ m{[/\\]}) {
        return MM->maybe_command($bin) || '';
    }

    # Otherwise we look for it in the path in a cross-platform way.
    my @path = $path ? @$path : File::Spec->path;
    foreach my $dir (@path) {
        next if !-d $dir;
        my $full_path = File::Spec->catfile($dir, $bin);
        # MM is an alias for ExtUtils::MM. maybe_command is nice
        # because it checks .com, .bat, .exe (etc.) on Windows.
        my $command = MM->maybe_command($full_path);
        return $command if $command;
    }

    return '';
}

sub get_version_and_os {
    # Display version information
    my @os_details = POSIX::uname;
    # 0 is the name of the OS, 2 is the major version,
    my $os_name = $os_details[0] . ' ' . $os_details[2];
    if (ON_WINDOWS) {
        require Win32;
        $os_name = Win32::GetOSName();
    }
    # $os_details[3] is the minor version.
    return { bz_ver   => BUGZILLA_VERSION,
             perl_ver => sprintf('%vd', $^V),
             os_name  => $os_name,
             os_ver   => $os_details[3] };
}

sub _extension_paths {
    my $dir = bz_locations()->{'extensionsdir'};
    my @extension_items = glob("$dir/*");
    my @paths;
    foreach my $item (@extension_items) {
        my $basename = basename($item);
        # Skip CVS directories and any hidden files/dirs.
        next if ($basename eq 'CVS' or $basename =~ /^\./);
        if (-d $item) {
            if (!-e "$item/disabled") {
                push(@paths, $item);
            }
        }
        elsif ($item =~ /\.pm$/i) {
            push(@paths, $item);
        }
    }
    return @paths;
}

sub extension_code_files {
    my ($requirements_only) = @_;
    my @files;
    foreach my $path (_extension_paths()) {
        my @load_files;
        if (-d $path) {
            my $extension_file = "$path/Extension.pm";
            my $config_file    = "$path/Config.pm";
            if (-e $extension_file) {
                push(@load_files, $extension_file);
            }
            if (-e $config_file) {
                push(@load_files, $config_file);
            }

            # Don't load Extension.pm if we just want Config.pm and
            # we found both.
            if ($requirements_only and scalar(@load_files) == 2) {
                shift(@load_files);
            }
        }
        else {
            push(@load_files, $path);
        }
        next if !scalar(@load_files);
        # We know that these paths are safe, because they came from
        # extensionsdir and we checked them specifically for their format.
        # Also, the only thing we ever do with them is pass them to "require".
        trick_taint($_) foreach @load_files;
        push(@files, \@load_files);
    }

    my @additional;
    my $datadir = bz_locations()->{'datadir'};
    my $addl_file = "$datadir/extensions/additional";
    if (-e $addl_file) {
        open(my $fh, '<', $addl_file) || die "$addl_file: $!";
        @additional = map { trim($_) } <$fh>;
        close($fh);
    }
    return (\@files, \@additional);
}

# Used by _get_extension_requirements in Bugzilla::Install::Requirements.
sub extension_requirement_packages {
    # If we're in a .cgi script or some time that's not the requirements phase,
    # just use Bugzilla->extensions. This avoids running the below code during
    # a normal Bugzilla page, which is important because the below code
    # doesn't actually function right if it runs after 
    # Bugzilla::Extension->load_all (because stuff has already been loaded).
    # (This matters because almost every page calls Bugzilla->feature, which
    # calls OPTIONAL_MODULES, which calls this method.)
    #
    # We check if Bugzilla.pm is already loaded, instead of doing a "require",
    # because we *do* want the code lower down to run during the Requirements
    # phase of checksetup.pl, instead of Bugzilla->extensions, and Bugzilla.pm
    # actually *can* be loaded during the Requirements phase if all the
    # requirements have already been installed.
    if ($INC{'Bugzilla.pm'}) {
        return Bugzilla->extensions;
    }
    my $packages = _cache()->{extension_requirement_packages};
    return $packages if $packages;
    $packages = [];
    my %package_map;
    
    my ($file_sets, $extra_packages) = extension_code_files('requirements only');
    foreach my $file_set (@$file_sets) {
        my $file = shift @$file_set;
        my $name = require $file;
        if ($name =~ /^\d+$/) {
            die install_string('extension_must_return_name',
                               { file => $file, returned => $name });
        }
        my $package = "Bugzilla::Extension::$name";
        if ($package->can('package_dir')) {
            $package->package_dir($file);
        }
        else {
            extension_package_directory($package, $file);
        }
        $package_map{$file} = $package;
        push(@$packages, $package);
    }
    foreach my $package (@$extra_packages) {
        eval("require $package") || die $@;
        push(@$packages, $package);
    }

    _cache()->{extension_requirement_packages} = $packages;
    # Used by Bugzilla::Extension->load if it's called after this method
    # (which only happens during checksetup.pl, currently).
    _cache()->{extension_requirement_package_map} = \%package_map;
    return $packages;
}

# Used in this file and in Bugzilla::Extension.
sub extension_template_directory {
    my $extension = shift;
    my $class = ref($extension) || $extension;
    my $base_dir = extension_package_directory($class);
    if ($base_dir eq bz_locations->{'extensionsdir'}) {
        return bz_locations->{'templatedir'};
    }
    return "$base_dir/template";
}

# Used in this file and in Bugzilla::Extension.
sub extension_web_directory {
    my $extension = shift;
    my $class = ref($extension) || $extension;
    my $base_dir = extension_package_directory($class);
    return "$base_dir/web";
}

# For extensions that are in the extensions/ dir, this both sets and fetches
# the name of the directory that stores an extension's "stuff". We need this
# when determining the template directory for extensions (or other things
# that are relative to the extension's base directory).
sub extension_package_directory {
    my ($invocant, $file) = @_;
    my $class = ref($invocant) || $invocant;

    # $file is set on the first invocation, store the value in the extension's
    # package for retrieval on subsequent calls
    my $var;
    {
        no warnings 'once';
        no strict 'refs';
        $var = \${"${class}::EXTENSION_PACKAGE_DIR"};
    }
    if ($file) {
        $$var = dirname($file);
    }
    my $value = $$var;

    # This is for extensions loaded from data/extensions/additional.
    if (!$value) {
        my $short_path = $class;
        $short_path =~ s/::/\//g;
        $short_path .= ".pm";
        my $long_path = $INC{$short_path};
        die "$short_path is not in \%INC" if !$long_path;
        $value = $long_path;
        $value =~ s/\.pm//;
    }
    return $value;
}

sub indicate_progress {
    my ($params) = @_;
    my $current = $params->{current};
    my $total   = $params->{total};
    my $every   = $params->{every} || 1;

    print "." if !($current % $every);
    if ($current == $total || $current % ($every * 60) == 0) {
        print "$current/$total (" . int($current * 100 / $total) . "%)\n";
    }
}

sub install_string {
    my ($string_id, $vars) = @_;
    _cache()->{install_string_path} ||= template_include_path();
    my $path = _cache()->{install_string_path};
    
    my $string_template;
    # Find the first template that defines this string.
    foreach my $dir (@$path) {
        my $base = "$dir/setup/strings";
        $string_template = _get_string_from_file($string_id, "$base.txt.pl")
            if !defined $string_template;
        last if defined $string_template;
    }
    
    die "No language defines the string '$string_id'"
        if !defined $string_template;

    utf8::decode($string_template) if !utf8::is_utf8($string_template);

    $vars ||= {};
    my @replace_keys = keys %$vars;
    foreach my $key (@replace_keys) {
        my $replacement = $vars->{$key};
        die "'$key' in '$string_id' is tainted: '$replacement'"
            if tainted($replacement);
        # We don't want people to start getting clever and inserting
        # ##variable## into their values. So we check if any other
        # key is listed in the *replacement* string, before doing
        # the replacement. This is mostly to protect programmers from
        # making mistakes.
        if (grep($replacement =~ /##$key##/, @replace_keys)) {
            die "Unsafe replacement for '$key' in '$string_id': '$replacement'";
        }
        $string_template =~ s/\Q##$key##\E/$replacement/g;
    }

    return $string_template;
}

sub _wanted_languages {
    my ($requested, @wanted);

    # Checking SERVER_SOFTWARE is the same as i_am_cgi() in Bugzilla::Util.
    if (exists $ENV{'SERVER_SOFTWARE'}) {
        my $cgi = eval { Bugzilla->cgi } || eval { require CGI; return CGI->new() };
        $requested = $cgi->http('Accept-Language') || '';
        my $lang = $cgi->cookie('LANG');
        push(@wanted, $lang) if $lang;
    }
    else {
        $requested = get_console_locale();
    }

    push(@wanted, _sort_accept_language($requested));
    return \@wanted;
}

sub _wanted_to_actual_languages {
    my ($wanted, $supported) = @_;

    my @actual;
    foreach my $lang (@$wanted) {
        # If we support the language we want, or *any version* of
        # the language we want, it gets pushed into @actual.
        #
        # Per RFC 1766 and RFC 2616, things like 'en' match 'en-us' and
        # 'en-uk', but not the other way around. (This is unfortunately
        # not very clearly stated in those RFC; see comment just over 14.5
        # in http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4)
        my @found = grep(/^\Q$lang\E(-.+)?$/i, @$supported);
        push(@actual, @found) if @found;
    }

    # We always include English at the bottom if it's not there, even if
    # it wasn't selected by the user.
    if (!grep($_ eq 'en', @actual)) {
        push(@actual, 'en');
    }

    return \@actual;
}

sub supported_languages {
    my $cache = _cache();
    return $cache->{supported_languages} if $cache->{supported_languages};

    my @dirs = glob(bz_locations()->{'templatedir'} . "/*");
    my @languages;
    foreach my $dir (@dirs) {
        # It's a language directory only if it contains "default" or
        # "custom". This auto-excludes CVS directories as well.
        next if (!-d "$dir/default" and !-d "$dir/custom");
        my $lang = basename($dir);
        # Check for language tag format conforming to RFC 1766.
        next unless $lang =~ /^[a-zA-Z]{1,8}(-[a-zA-Z]{1,8})?$/;
        push(@languages, $lang);
    }

    $cache->{supported_languages} = \@languages;
    return \@languages;
}

sub include_languages {
    my ($params) = @_;

    # Basically, the way this works is that we have a list of languages
    # that we *want*, and a list of languages that Bugzilla actually
    # supports.
    my $wanted;
    if ($params->{language}) {
        # We can pass several languages at once as an arrayref
        # or a single language.
        $wanted = $params->{language};
        $wanted = [$wanted] unless ref $wanted;
    }
    else {
        $wanted = _wanted_languages();
    }
    my $supported = supported_languages();
    my $actual    = _wanted_to_actual_languages($wanted, $supported);
    return @$actual;
}

# Used by template_include_path
sub _template_lang_directories {
    my ($languages, $templatedir) = @_;
    
    my @add = qw(custom default);
    my $project = bz_locations->{'project'};
    unshift(@add, $project) if $project;

    my @result;
    foreach my $lang (@$languages) {
        foreach my $dir (@add) {
            my $full_dir = "$templatedir/$lang/$dir";
            if (-d $full_dir) {
                trick_taint($full_dir);
                push(@result, $full_dir);
            }
        }
    }
    return @result;
}

# Used by template_include_path.
sub _template_base_directories {
    # First, we add extension template directories, because extension templates
    # override standard templates. Extensions may be localized in the same way
    # that Bugzilla templates are localized.
    #
    # We use extension_requirement_packages instead of Bugzilla->extensions
    # because this fucntion is called during the requirements phase of 
    # installation (so Bugzilla->extensions isn't available).
    my $extensions = extension_requirement_packages();
    my @template_dirs;
    foreach my $extension (@$extensions) {
        my $dir;
        # If there's a template_dir method available in the extension
        # package, then call it. Note that this has to be defined in
        # Config.pm for extensions that have a Config.pm, to be effective
        # during the Requirements phase of checksetup.pl.
        if ($extension->can('template_dir')) {
            $dir = $extension->template_dir;
        }
        else {
            $dir = extension_template_directory($extension);
        }
        if (-d $dir) {
            push(@template_dirs, $dir);
        }
    }

    # Extensions may also contain *only* templates, in which case they
    # won't show up in extension_requirement_packages.
    foreach my $path (_extension_paths()) {
        next if !-d $path;
        if (!-e "$path/Extension.pm" and !-e "$path/Config.pm"
            and -d "$path/template") 
        {
            push(@template_dirs, "$path/template");
        }
    }


    push(@template_dirs, bz_locations()->{'templatedir'});
    return \@template_dirs;
}

sub template_include_path {
    my ($params) = @_;
    my @used_languages = include_languages($params);
    # Now, we add template directories in the order they will be searched:
    my $template_dirs = _template_base_directories(); 

    my @include_path;
    foreach my $template_dir (@$template_dirs) {
        my @lang_dirs = _template_lang_directories(\@used_languages, 
                                                   $template_dir);
        # Hooks get each set of extension directories separately.
        if ($params->{hook}) {
            push(@include_path, \@lang_dirs);
        }
        # Whereas everything else just gets a whole INCLUDE_PATH.
        else {
            push(@include_path, @lang_dirs);
        }
    }
    return \@include_path;
}

# This is taken straight from Sort::Versions 1.5, which is not included
# with perl by default.
sub vers_cmp {
    my ($a, $b) = @_;

    # Remove leading zeroes - Bug 344661
    $a =~ s/^0*(\d.+)/$1/;
    $b =~ s/^0*(\d.+)/$1/;

    my @A = ($a =~ /([-.]|\d+|[^-.\d]+)/g);
    my @B = ($b =~ /([-.]|\d+|[^-.\d]+)/g);

    my ($A, $B);
    while (@A and @B) {
        $A = shift @A;
        $B = shift @B;
        if ($A eq '-' and $B eq '-') {
            next;
        } elsif ( $A eq '-' ) {
            return -1;
        } elsif ( $B eq '-') {
            return 1;
        } elsif ($A eq '.' and $B eq '.') {
            next;
        } elsif ( $A eq '.' ) {
            return -1;
        } elsif ( $B eq '.' ) {
            return 1;
        } elsif ($A =~ /^\d+$/ and $B =~ /^\d+$/) {
            if ($A =~ /^0/ || $B =~ /^0/) {
                return $A cmp $B if $A cmp $B;
            } else {
                return $A <=> $B if $A <=> $B;
            }
        } else {
            $A = uc $A;
            $B = uc $B;
            return $A cmp $B if $A cmp $B;
        }
    }
    @A <=> @B;
}

sub no_checksetup_from_cgi {
    print "Content-Type: text/html; charset=UTF-8\r\n\r\n";
    print install_string('no_checksetup_from_cgi');
    exit;
}

######################
# Helper Subroutines #
######################

# Used by install_string
sub _get_string_from_file {
    my ($string_id, $file) = @_;
    # If we already loaded the file, then use its copy from the cache.
    if (my $strings = _cache()->{strings_from_file}->{$file}) {
        return $strings->{$string_id};
    }

    # This module is only needed by checksetup.pl,
    # so only load it when needed.
    require Safe;

    return undef if !-e $file;
    my $safe = new Safe;
    $safe->rdo($file);
    my %strings = %{$safe->varglob('strings')};
    _cache()->{strings_from_file}->{$file} = \%strings;
    return $strings{$string_id};
}

# Make an ordered list out of a HTTP Accept-Language header (see RFC 2616, 14.4)
# We ignore '*' and <language-range>;q=0
# For languages with the same priority q the order remains unchanged.
sub _sort_accept_language {
    sub sortQvalue { $b->{'qvalue'} <=> $a->{'qvalue'} }
    my $accept_language = $_[0];

    # clean up string.
    $accept_language =~ s/[^A-Za-z;q=0-9\.\-,]//g;
    my @qlanguages;
    my @languages;
    foreach(split /,/, $accept_language) {
        if (m/([A-Za-z\-]+)(?:;q=(\d(?:\.\d+)))?/) {
            my $lang   = $1;
            my $qvalue = $2;
            $qvalue = 1 if not defined $qvalue;
            next if $qvalue == 0;
            $qvalue = 1 if $qvalue > 1;
            push(@qlanguages, {'qvalue' => $qvalue, 'language' => $lang});
        }
    }

    return map($_->{'language'}, (sort sortQvalue @qlanguages));
}

sub get_console_locale {
    require Locale::Language;
    my $locale = setlocale(LC_CTYPE);
    my $language;
    # Some distros set e.g. LC_CTYPE = fr_CH.UTF-8. We clean it up.
    if ($locale =~ /^([^\.]+)/) {
        $locale = $1;
    }
    $locale =~ s/_/-/;
    # It's pretty sure that there is no language pack of the form fr-CH
    # installed, so we also include fr as a wanted language.
    if ($locale =~ /^(\S+)\-/) {
        $language = $1;
        $locale .= ",$language";
    }
    else {
        $language = $locale;
    }

    # Some OSs or distributions may have setlocale return a string of the form
    # German_Germany.1252 (this example taken from a Windows XP system), which
    # is unsuitable for our needs because Bugzilla works on language codes.
    # We try and convert them here.
    if ($language = Locale::Language::language2code($language)) {
        $locale .= ",$language";
    }

    return $locale;
}

sub set_output_encoding {
    # If we've already set an encoding layer on STDOUT, don't
    # add another one.
    my @stdout_layers = PerlIO::get_layers(STDOUT);
    return if grep(/^encoding/, @stdout_layers);

    my $encoding;
    if (ON_WINDOWS and eval { require Win32::Console }) {
        # Although setlocale() works on Windows, it doesn't always return
        # the current *console's* encoding. So we use OutputCP here instead,
        # when we can.
        $encoding = Win32::Console::OutputCP();
    }
    else {
        my $locale = setlocale(LC_CTYPE);
        if ($locale =~ /\.([^\.]+)$/) {
            $encoding = $1;
        }
    }
    $encoding = "cp$encoding" if ON_WINDOWS;

    $encoding = Encode::resolve_alias($encoding) if $encoding;
    if ($encoding and $encoding !~ /utf-8/i) {
        binmode STDOUT, ":encoding($encoding)";
        binmode STDERR, ":encoding($encoding)";
    }
    else {
        binmode STDOUT, ':utf8';
        binmode STDERR, ':utf8';
    }
}

sub init_console {
    eval { ON_WINDOWS && require Win32::Console::ANSI; };
    $ENV{'ANSI_COLORS_DISABLED'} = 1 if ($@ || !-t *STDOUT);
    $SIG{__DIE__} = \&_console_die;
    prevent_windows_dialog_boxes();
    set_output_encoding();
}

sub _console_die {
    my ($message) = @_;
    # $^S means "we are in an eval"
    if ($^S) {
        die $message;
    }
    # Remove newlines from the message before we color it, and then
    # add them back in on display. Otherwise the ANSI escape code
    # for resetting the color comes after the newline, and Perl thinks
    # that it should put "at Bugzilla/Install.pm line 1234" after the
    # message.
    $message =~ s/\n+$//;
    # We put quotes around the message to stringify any object exceptions,
    # like Template::Exception.
    die colored("$message", COLOR_ERROR) . "\n";
}

sub success {
    my ($message) = @_;
    print colored($message, COLOR_SUCCESS), "\n";
}

sub prevent_windows_dialog_boxes {
    # This code comes from http://bugs.activestate.com/show_bug.cgi?id=82183
    # and prevents Perl modules from popping up dialog boxes, particularly
    # during checksetup (since loading DBD::Oracle during checksetup when
    # Oracle isn't installed causes a scary popup and pauses checksetup).
    #
    # Win32::API ships with ActiveState by default, though there could 
    # theoretically be a Windows installation without it, I suppose.
    if (ON_WINDOWS and eval { require Win32::API }) {
        # Call kernel32.SetErrorMode with arguments that mean:
        # "The system does not display the critical-error-handler message box.
        # Instead, the system sends the error to the calling process." and
        # "A child process inherits the error mode of its parent process."
        my $SetErrorMode = Win32::API->new('kernel32', 'SetErrorMode', 
                                           'I', 'I');
        my $SEM_FAILCRITICALERRORS = 0x0001;
        my $SEM_NOGPFAULTERRORBOX  = 0x0002;
        $SetErrorMode->Call($SEM_FAILCRITICALERRORS | $SEM_NOGPFAULTERRORBOX);
    }
}

# This is like request_cache, but it's used only by installation code
# for checksetup.pl and things like that.
our $_cache = {};
sub _cache {
    # If the normal request_cache is available (which happens any time
    # after the requirements phase) then we should use that.
    if (eval { Bugzilla->request_cache; }) {
        return Bugzilla->request_cache;
    }
    return $_cache;
}

###############################
# Copied from Bugzilla::Util #
##############################

sub trick_taint {
    require Carp;
    Carp::confess("Undef to trick_taint") unless defined $_[0];
    my $match = $_[0] =~ /^(.*)$/s;
    $_[0] = $match ? $1 : undef;
    return (defined($_[0]));
}

sub trim {
    my ($str) = @_;
    if ($str) {
      $str =~ s/^\s+//g;
      $str =~ s/\s+$//g;
    }
    return $str;
}

__END__

=head1 NAME

Bugzilla::Install::Util - Utility functions that are useful both during
installation and afterwards.

=head1 DESCRIPTION

This module contains various subroutines that are used primarily
during installation. However, these subroutines can also be useful to
non-installation code, so they have been split out into this module.

The difference between this module and L<Bugzilla::Util> is that this
module is safe to C<use> anywhere in Bugzilla, even during installation,
because it depends only on L<Bugzilla::Constants> and built-in perl modules.

None of the subroutines are exported by default--you must explicitly
export them.

=head1 SUBROUTINES

=over

=item C<bin_loc>

On *nix systems, given the name of a binary, returns the path to that
binary, if the binary is in the C<PATH>.

=item C<get_version_and_os>

Returns a hash containing information about what version of Bugzilla we're
running, what perl version we're using, and what OS we're running on.

=item C<get_console_locale>

Returns the language to use based on the LC_CTYPE value returned by the OS.
If LC_CTYPE is of the form fr-CH, then fr is appended to the list.

=item C<init_console>

Sets the C<ANSI_COLORS_DISABLED> and C<HTTP_ACCEPT_LANGUAGE> environment variables.

=item C<indicate_progress>

=over

=item B<Description>

This prints out lines of dots as a long update is going on, to let the user
know where we are and that we're not frozen. A new line of dots will start
every 60 dots.

Sample usage: C<indicate_progress({ total =E<gt> $total, current =E<gt>
$count, every =E<gt> 1 })>

=item B<Sample Output>

Here's some sample output with C<total = 1000> and C<every = 10>:

 ............................................................600/1000 (60%)
 ........................................

=item B<Params>

=over

=item C<total> - The total number of items we're processing.

=item C<current> - The number of the current item we're processing.

=item C<every> - How often the function should print out a dot.
For example, if this is 10, the function will print out a dot every
ten items. Defaults to 1 if not specified.

=back

=item B<Returns>: nothing

=back

=item C<install_string>

=over

=item B<Description>

This is a very simple method of templating strings for installation.
It should only be used by code that has to run before the Template Toolkit
can be used. (See the comments at the top of the various L<Bugzilla::Install>
modules to find out when it's safe to use Template Toolkit.)

It pulls strings out of the F<strings.txt.pl> "template" and replaces
any variable surrounded by double-hashes (##) with a value you specify.

This allows for localization of strings used during installation.

=item B<Example>

Let's say your template string looks like this:

 The ##animal## jumped over the ##plant##.

Let's say that string is called 'animal_jump_plant'. So you call the function
like this:

 install_string('animal_jump_plant', { animal => 'fox', plant => 'tree' });

That will output this:

 The fox jumped over the tree.

=item B<Params>

=over

=item C<$string_id> - The name of the string from F<strings.txt.pl>.

=item C<$vars> - A hashref containing the replacement values for variables
inside of the string.

=back

=item B<Returns>: The appropriate string, with variables replaced.

=back

=item C<template_include_path>

Used by L<Bugzilla::Template> and L</install_string> to determine the
directories where templates are installed. Templates can be installed
in many places. They're listed here in the basic order that they're
searched:

=over

=item extensions/C<$extension>/template/C<$language>/C<$project>

=item extensions/C<$extension>/template/C<$language>/custom

=item extensions/C<$extension>/template/C<$language>/default

=item template/C<$language>/C<$project>

=item template/C<$language>/custom

=item template/C<$language>/default

=back

C<$project> has to do with installations that are using the C<$ENV{PROJECT}>
variable to have different "views" on a single Bugzilla.

The F<default> directory includes templates shipped with Bugzilla.

The F<custom> directory is a directory for local installations to override
the F<default> templates. Any individual template in F<custom> will
override a template of the same name and path in F<default>.

C<$language> is a language code, C<en> being the default language shipped
with Bugzilla. Localizers ship other languages.

C<$extension> is the name of any directory in the F<extensions/> directory.
Each extension has its own directory.

Note that languages are sorted by the user's preference (as specified
in their browser, usually), and extensions are sorted alphabetically.

=item C<include_languages>

Used by L<Bugzilla::Template> to determine the languages' list which 
are compiled with the browser's I<Accept-Language> and the languages 
of installed templates.

=item C<vers_cmp>

=over

=item B<Description>

This is a comparison function, like you would use in C<sort>, except that
it compares two version numbers. So, for example, 2.10 would be greater
than 2.2.

It's based on versioncmp from L<Sort::Versions>, with some Bugzilla-specific
fixes.

=item B<Params>: C<$a> and C<$b> - The versions you want to compare.

=item B<Returns>

C<-1> if C<$a> is less than C<$b>, C<0> if they are equal, or C<1> if C<$a>
is greater than C<$b>.

=back

=back