[debian/debian-policy.git] / perl-policy.sgml

<!doctype debiandoc system [
<!-- include version information so we don't have to hard code it
     within the document -->
<!entity % versiondata SYSTEM "version.ent"> %versiondata;
]>

<debiandoc>
  <book>
    <titlepag>
      <title>Debian Perl Policy</title>
      <author>
        <name>Rapha&euml;l Hertzog</name>
      </author>
      <author>
        <name>Brendan O'Dea</name>
      </author>
      <author>
        <name>The Debian Policy mailing list</name>
        <email>debian-policy@lists.debian.org</email>
      </author>
      <version>version &version;, &date;</version>

      <abstract>
        This document describes the packaging of Perl within the Debian
        distribution and the policy requirements for packaged
        Perl programs and modules.
      </abstract>

      <copyright>
        <copyrightsummary>
          Copyright &copy; 1999, 2001 Software in the Public Interest
        </copyrightsummary>
        <p>
          This manual is free software; you can redistribute it and/or
          modify it under the terms of the GNU General Public License
          as published by the Free Software Foundation; either version
          2 of the License, or (at your option) any later version.
        </p>
        <p>
          This is distributed in the hope that it will be useful, but
          WITHOUT ANY WARRANTY; without even the implied warranty of
          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
          the GNU General Public License for more details.
        </p>
        <p>
          A copy of the GNU General Public License is available as
          <tt>/usr/share/common-licenses/GPL</tt> in the Debian
          distribution or on the World Wide Web at 
          <url id="http://www.gnu.org/copyleft/gpl.html"
          name="The GNU Public Licence">.
        </p>
        <p>
          You can also obtain it by writing to the
          Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
          Boston, MA 02110-1301, USA. 
        </p>
      </copyright>
    </titlepag>

    <toc detail="sect">

    <chapt>
      <heading>About this document</heading>
      <p>
        This document is distributed as the <tt>perl-policy</tt> files
        in the Debian package
        <package><url name="debian-policy" id="http://packages.debian.org/debian-policy"></package>.
        It is also available from the Debian web mirrors at
        <tt><url name="/doc/packaging-manuals/perl-policy/"
                id="http://www.debian.org/doc/packaging-manuals/perl-policy/"></tt>.
      </p>
    </chapt>

    <chapt id="perl">
      <heading>Perl Packaging</heading>
      <sect id="versions">
        <heading>Versions</heading>
        <p>
          At any given time, the package <package>perl</package> should
          represent the current stable upstream version of Perl revision
          5 (see <ref id="perl6">).
        </p>
        <p>
          Only one package may contain the <file>/usr/bin/perl</file>
          binary and that package must either be <package>perl</package>
          or a dependency of that package (see <ref id="base">).
        </p>
        <p>
          Where possible, Perl should be compiled to provide binary
          compatibility to at least the last released package version to
          allow a grace period over which binary module packages may be
          re-built against the new package (see <ref id="binary_modules">).
        </p>
        <p>
          The <package>perl-base</package> package must provide
          <package>perlapi-<var>abiname</var></package> for all released
          package versions it is compatible with. The choice of
          <var>abiname</var> is arbitrary, but if it differs from
          <tt>$Config{version}</tt>, it must be specified in
          <tt>$Config{debian_abi}</tt>.
        </p>
      </sect>

      <sect id="base">
        <heading>Base Package</heading>
        <p>
          In order to provide a minimal installation of Perl for use by
          applications without requiring the whole of Perl to be
          installed, the <package>perl-base</package> package contains
          the binary and a basic set of modules.
        </p>
        <p>
          As Perl has been part of the essential set for some time and is
          used without dependencies by such things as package maintainer
          scripts, <package>perl-base</package> must be
          priority <em>required</em> and marked as <em>essential</em>.
        </p>
        <p>
          Note that the <package>perl-base</package> package is intended
          only to provide for exceptional circumstances and the contents
          may change.  In general, only packages which form part of the
          base system should use only the facilities
          of <package>perl-base</package> rather than declaring a
          dependency on <package>perl</package>.
        </p>
      </sect>

      <sect id="paths">
        <heading>Module Path</heading>
        <p>
          Perl searches three different locations for modules, referred
          to in this document as <var>core</var> in which modules
          distributed with Perl are installed, <var>vendor</var> for
          packaged modules and <var>site</var> for modules installed by
          the local administrator.
        </p>
        <p>
          The module search path (<tt>@INC</tt>) in the Debian packages
          has been ordered to include these locations in the following
          order:
          <taglist>
            <tag><var>site</var> (current)</tag>
            <item>
              <p>
                Modules installed by the local administrator for the
                current version of Perl (see <ref id="site">).
                <example>
/usr/local/lib/perl/<var>version</var>
/usr/local/share/perl/<var>version</var>
                </example>
                Where <var>version</var> indicates the current Perl
                version (<tt>$Config{version}</tt><footnote>see the
                <tt>Config</tt> module</footnote>).
              </p>
            </item>
            <tag><var>vendor</var></tag>
            <item>
              <p>
                Packaged modules (see <ref id="module_packages">).
                <example>
/usr/lib/perl5
/usr/share/perl5
                </example>
              </p>
            </item>
            <tag><var>core</var></tag>
            <item>
              <p>
                Modules included in the core Perl distribution.
                <example>
/usr/lib/perl/<var>shortversion</var>
/usr/share/perl/<var>shortversion</var>
                </example>
                Where <var>shortversion</var> indicates the current Perl major
                version (for example <tt>5.18</tt>).
              </p>
            </item>
            <tag><var>site</var> (old)</tag>
            <item>
              <p>
                <var>site</var> directories (as above) for modules
                installed with previously released
                <package>perl</package> packages for which the current
                package is binary compatible are included if present.
              </p>
            </item>
          </taglist>
          In each of the directory pairs above, the <file>lib</file>
          component is for binary (XS) modules, and <file>share</file>
          for architecture-independent (pure-perl) modules.
        </p>
      </sect>

      <sect id="docs">
        <heading>Documentation</heading>
        <p>
          The POD files and manual pages which do not refer to programs
          may be split out into a separate <package>perl-doc</package>
          package.
        </p>
        <p>
          Manual pages distributed with packages built from the perl
          source package must be installed into the standard directories:
          <taglist>
            <tag>Programs</tag>
            <item>
              <p>
                Manual pages for programs and scripts are installed into
                <file>/usr/share/man/man1</file> with the extension
                <tt>.1</tt>.
              </p>
            </item>
            <tag>Modules</tag>
            <item>
              <p>
                Manual pages for modules are installed into
                <file>/usr/share/man/man3</file> with the extension
                <tt>.3perl</tt>.
              </p>
            </item>
          </taglist>
          The extensions used for manual pages distributed with module
          packages are different.  See <ref id="vendor_dirs">.
        </p>
      </sect>
    </chapt>

    <chapt id="site">
      <heading>Locally Installed Modules</heading>
      <sect id="site_dirs">
        <heading>Site Directories</heading>
        <p>
          The Perl packages must provide a mechanism for the local
          administrator to install modules under <file>/usr/local</file>
          but must not create or remove those directories.
        </p>
        <p>
          Modules should be installed to the directories described above
          in <ref id="paths"> as <var>site</var> (current), programs to
          <file>/usr/local/bin</file> and manual pages under
          <file>/usr/local/man</file>.
        </p>
      </sect>

      <sect id="site_install">
        <heading>Site Installation</heading>
        <p>
          The following commands should be sufficient in the majority of
          cases for the local administrator to install modules and must
          create directories as required:
          <example>
perl Makefile.PL
make install
          </example>
        </p>
      </sect>
    </chapt>

    <chapt id="module_packages">
      <heading>Packaged Modules</heading>
      <sect id="vendor_dirs">
        <heading>Vendor Directories</heading>
        <p>
          The installation directory for Debian modules must be
          different from that for <var>core</var> and <var>site</var>
          modules.
        </p>
        <p>
          The current Perl packaging uses the <var>vendor</var>
          directories for this purpose, which are at present as
          described in <ref id="paths"> as <var>vendor</var>.
        </p>
        <p>
          No version subdirectory exists on these directories as the
          dependencies for packaged modules (see <ref id="module_deps">)
          should ensure that all work with the current
          <package>perl</package> package.
        </p>
        <p>
          The Perl distribution includes many modules available
          separately from CPAN<footnote><url
          id="http://www.perl.com/CPAN"></footnote>, which may have a
          newer version.  The intent of the <tt>@INC</tt> ordering
          (described in <ref id="paths">) is to allow such modules to be
          packaged to <var>vendor</var> which take precedence over the
          version in <var>core</var>.  A packaged module which shadows a
          <var>core</var> module in this way must be a newer version.
        </p>
        <p>
          Module packages must install manual pages into the standard
          directories (see <ref id="docs">) using the extensions
          <tt>.1p</tt> and <tt>.3pm</tt> to ensure that no conflict
          arises where a packaged module duplicates a <var>core</var>
          module.
        </p>
        <p>
          <file>.packlist</file> files should not be installed.
        </p>
      </sect>

      <sect id="package_names">
        <heading>Module Package Names</heading>
        <p>
          Perl module packages should be named for the primary module
          provided.  The naming convention is to lowercase the Perl module
          name, prepend, <tt>lib</tt>, change all occurrences
          of <tt>::</tt> to <tt>-</tt>, and append <tt>-perl</tt>.  For
          example:
          <example>
Foo::Bar        libfoo-bar-perl
Foo::Bar::Baz   libfoo-bar-baz-perl
Foo::BarBaz     libfoo-barbaz-perl
          </example>
          Packages which include multiple modules may additionally include
          provides for the additional modules using the same convention.
        </p>
      </sect>

      <sect id="vendor_install">
        <heading>Vendor Installation</heading>
        <p>
          A module should use the following lines in the
          <file>debian/rules</file> <tt>build</tt>
          target<footnote>The environment variable <tt>PERL_MM_OPT</tt>
          may be used to pass the <tt>INSTALLDIRS=vendor</tt> option in
          cases where <file>Makefile.PL</file> is not invoked directly
          from <file>debian/rules</file></footnote>:
          <example>
perl Makefile.PL INSTALLDIRS=vendor
$(MAKE) OPTIMIZE="-O2 -g -Wall"
          </example>
          and this one to install the results into the temporary tree:
          <example>
$(MAKE) install DESTDIR=$(CURDIR)/debian/&lt;tmp&gt;
          </example><footnote>
            <p>Replace &lt;tmp&gt; with the appropriate directory
            (nominally just tmp)</p>
          </footnote>
        </p>
      </sect>

      <sect id="module_deps">
        <heading>Module Dependencies</heading>
        <sect1 id="indep_modules">
          <heading>Architecture-Independent Modules</heading>
          <p>
            Architecture-independent modules which require
            <var>core</var> modules from the <package>perl</package>
            package must specify a dependency on that package.
          </p>
          <p>
            Modules which contain explicit <tt>require
            <var>version</var></tt> or <tt>use <var>version</var></tt>
            statements must specify a dependency on
            <package>perl</package> or <package>perl-base</package> with
            the minimum required version, or more simply the current
            version.
          </p>
        </sect1>

        <sect1 id="binary_modules">
          <heading>Binary Modules</heading>
          <p>
            Binary modules must specify a dependency on either
            <package>perl</package> or <package>perl-base</package> with
            a minimum version of the <package>perl</package> package
            used to build the module, and must additionally depend on
            the expansion of
            <package>perlapi-$Config{debian_abi}</package> using
            the <tt>Config</tt> module. If <tt>$Config{debian_abi}</tt>
            is empty or not set, <tt>$Config{version}</tt> must be used.
          </p>
        </sect1>

        <sect1 id="dh_perl">
          <heading>Automating Perl Dependencies</heading>
          <p>
            Rather than hard-coding the dependencies into the control
            file, using a substitution such as <tt>${perl:Depends}</tt>
            is suggested.  This allows the dependencies to be determined
            at build time and written to the <file>substvars</file> file
            in the form
            <tt>perl:Depends=<var>deps</var></tt>.<footnote>
              <p>Please note that dependencies caused by versioned
              uses and on separately packaged modules are not included
              in this variable and must be explicitly included.</p>
            </footnote>
          </p>
          <p>
            Packages built with <prgn>debhelper</prgn> may use

            <manref name="dh_perl" section="1"> to generate this
            substitution automatically.  This additionally requires a
            versioned <tt>Build-Depends</tt> (or
            <tt>Build-Depends-Indep</tt>) on <tt>debhelper (>=
            3.0.18)</tt>.
          </p>
        </sect1>
      </sect>
    </chapt>

    <chapt id="programs">
      <heading>Perl Programs</heading>
      <sect id="hash_bang">
        <heading>Script Magic</heading>
        <p>
          All packaged perl programs must start with
          <tt>#!/usr/bin/perl</tt> and may append such flags as are
          required.
        </p>
      </sect>

      <sect id="program_deps">
        <heading>Program Dependencies</heading>
        <p>
          Programs which require <var>core</var> modules from the
          <package>perl</package> package must specify a dependency on
          that package.
        </p>
        <p>
          Programs which contain explicit <tt>require
          <var>version</var></tt> or <tt>use <var>version</var></tt>
          statements must specify a dependency on
          <package>perl</package> or <package>perl-base</package> with
          the minimum required version, or more simply the current
          version.
        </p>
        <p>
          As with modules, packages using <prgn>debhelper</prgn> may use
          <manref name="dh_perl" section="1"> to automatically generate
          dependences (see <ref id="dh_perl">).
        </p>
      </sect>
    </chapt>

    <chapt id="embed">
      <heading>Programs Embedding Perl</heading>
      <sect id="build_embedded">
        <heading>Building Embedded Programs</heading>
        <p>
          Programs which embed a perl interpreter must declare a
          <tt>Build-Depends</tt> on <package>libperl-dev</package>.
        </p>
        <p>
          The default linker options produced by
          <example>
perl -MExtUtils::Embed -e ldopts
          </example>
          will link against the dynamic <tt>libperl</tt>.  If programs
          wish to link to the static library, then <tt>-lperl</tt>
          should be changed to <file>/usr/lib/libperl.a</file> in those
          options.
        </p>
      </sect>

      <sect id="embedded_deps">
        <heading>Embedded Perl Dependencies</heading>
        <p>
          Dependencies for programs linking against the shared Perl
          library will be automatically created by
          <prgn>dpkg-shlibdeps</prgn>.  Note however that the shared
          perl library package only suggests
          <package>perl-base</package> and packages requiring any
          <var>core</var> modules from the <package>perl</package>
          package must depend upon it explicitly.
        </p>
      </sect>

      <sect id="perl_upgrades">
        <heading>Perl Package Upgrades</heading>
        <p>
          Starting from <package>perl</package> 5.12.3-2, a dpkg trigger
          named <var>perl-major-upgrade</var> will be triggered by the
          postinst of the <package>perl</package> package during major
          upgrades. Some examples of things which constitute a major upgrade
          are an upgrade which would change the value of versioned
          directories in <tt>@INC</tt>, or one which changes <tt>abiname</tt>.
          Any package may declare an interest in the trigger, especially
          packages including long-running daemons which would stop working
          until restart.
        </p>
        <p>
          It is suggested that such packages include an appropriate section
          in their postinst to handle the trigger by restarting relevant
          daemons or notifying users of further action.
        </p>
      </sect>
    </chapt>

    <appendix id="perl6">
      <heading>Perl 6</heading>
      <p>
        The current stable upstream version at the time of this writing
        is 5.6.0.  There is currently work in progress on the next major
        revision, although the specifications have yet to be finalised.
      </p>
      <p>
        It is anticipated that when Perl 6 is released it will initially
        be packaged as <package>perl6</package>, install the binary as
        <file>/usr/bin/perl6</file> and use different directories for
        packaged modules to <package>perl</package>:
        <example>
/usr/lib/perl6
/usr/share/perl6
        </example>
        This will allow Perl 5 and 6 packages and modules (which should
        be packaged as <package>libfoo-bar-perl6</package>), to co-exist
        for as long as required.
      </p>
      <p>
        At some stage in the future when Perl 6 is sufficiently mature,
        the package naming may be reversed such that the
        <package>perl</package> package contains Perl 6 and the current
        package becomes <package>perl5</package>.
      </p>
    </appendix>
  </book>
</debiandoc>
<!-- Local variables: -->
<!-- indent-tabs-mode: t -->
<!-- End: -->