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+=head1 NAME
+
+pg_buildext - Build and install a PostgreSQL extension
+
+=head1 SYNOPSIS
+
+B<pg_buildext> [I<options>] I<action> [I<src-dir>] [I<arguments>]
+
+=head1 DESCRIPTION
+
+B<pg_buildext> is a script that will build a PostgreSQL extension in a C<VPATH>
+way, for potentially several PostgreSQL server versions in parallel.
+It builds for the intersection of versions known in
+C<debian/pgversions> (versions supported by the package) and in
+C</usr/share/postgresql-common/supported-versions> (versions supported in this
+release).
+
+Many PostgreSQL extension packages require no special handling at build time
+and can use B<dh $@ --with pgxs> or B<dh $@ --with pgxs_loop> to
+automatically execute the steps outlined below.
+
+=head1 USAGE
+
+Packages using B<pg_buildext> should be prepared to build binaries for
+PostgreSQL versions that are not present in Debian unstable, e.g. for older
+releases when building backports for Debian (old)stable (possibly including
+backports of newer PostgreSQL releases), or for all PostgreSQL releases when
+the package is built for B<apt.postgresql.org>.
+
+As the set of binary packages depends on the target PostgreSQL versions,
+C<debian/control> is generated from a template in C<debian/control.in> when
+B<pg_buildext updatecontrol> is run.
+Package sections that contain B<PGVERSION> in the package name are replaced by
+a list of sections, filling in the supported PostgreSQL versions.
+Package sections that contain B<PGVERSION> outside the package name have the
+newest supported PostgreSQL version filled in (useful for meta packages).
+Include
+C</usr/share/postgresql-common/pgxs_debian_control.mk> in C<debian/rules> to
+run a check at build time if updating debian/control is required.
+
+As B<pg_buildext> invokes B<make> for the B<build>, B<install>, and B<clean>
+actions, invocations from C<debian/rules> (which is a makefile) should be prefixed
+with B<+> so the sub-makes can talk with the make jobserver. Additional makefile
+variables can be passed to B<make> via the B<-m> option.
+
+Many extensions support B<make installcheck> testing using B<pg_regress>. As
+this needs the package to be installed, it cannot be run at build time.
+Instead, the tests should be run using B<autopkgtest> from C<debian/tests/*>.
+
+If C<debian/tests/control.in> exists, occurrences of package names containing
+B<PGVERSION> are replaced by lists of package names with the target PostgreSQL
+versions filled in. (If no replacing is needed in C<debian/tests/control>, it
+is fine to provide the tests control file directly.)
+
+=head1 OPTIONS
+
+=over 4
+
+=item B<-cio> I<arg>
+
+=item B<-s>
+
+Passed to B<pg_virtualenv> when running B<installcheck>.
+
+=item B<-m> I<arg>
+
+Passed to B<make>.
+
+=back
+
+=head1 ACTIONS
+
+Most actions expect a directory name where to build the sources. It will get
+created for you if it does not exist. If the I<build-dir> contains a C<%v>
+sign, it will get replaced by the specific version of PostgreSQL being built
+against. (Usually this parameter is C<build-%v>.)
+
+=over 4
+
+=item B<supported-versions>
+
+Print effective list of supported versions, i.e. the intersection of the sets
+of versions supported by the system
+(from C</usr/share/postgresql-common/supported-versions>) and the package
+(from C<debian/pgversions>).
+
+Use this when building packages.
+
+=item B<installed-versions>
+
+In the list of installed packages, look for packages matching the B<PGVERSION>
+package name templates from C<debian/control.in>, and print the PostgreSQL
+major version number part.
+
+Use this when testing packages.
+
+=item B<checkcontrol>
+
+Check if C<debian/control> needs updating from C<debian/control.in>. This is
+invoked from C</usr/share/postgresql-common/pgxs_debian_control.mk>. When
+building for a B<backports> or B<pgdg> suite as determined by
+C<debian/changelog>, this action also updates the control file. Otherwise,
+B<updatecontrol> needs to be run manually.
+
+=item B<updatecontrol>
+
+Update C<debian/control> from C<debian/control.in>, and C<debian/tests/control>
+from C<debian/tests/control.in> if the latter exists.
+
+=item B<configure> [I<src-dir>] I<build-dir> [I<extra-configure-options>]
+
+For every supported version, call B<../configure> from the I<build-dir>
+directory. (Most PostgreSQL extensions do not have a configure script.)
+
+=item B<build> [I<src-dir>] I<build-dir> [I<extra-cflags>]
+
+Build the extension in the I<build-dir> directory.
+
+=item B<install> [I<src-dir>] I<build-dir> I<package-pattern>
+
+Invoke B<make install> from the I<build-dir> directory.
+The third parameter specifies the package name to use. Most packages
+use B<postgresql-%v-pkgname>. Make will be
+called with DESTDIR="$(CURDIR)/debian/I<package>".
+
+The B<dpkg> substitution variable B<postgresql:Depends> is set to depend
+on the required PostgreSQL server package. For compatibility with previous
+packaging standards, the dependency is also added to B<misc:Depends> if
+postgresql:Depends is not used.
+
+=item B<clean> [I<src-dir>] [I<build-dir>] [I<package-pattern>]
+
+Clean the build directories.
+
+=item B<loop> [I<src-dir>] I<package-pattern>
+
+As a variant to calling B<build> and B<install> separately for VPATH builds,
+loop over the supported PostgreSQL versions in the top source directory. This
+should be used if the package does not support VPATH builds. As it also invokes
+B<make install>, it should be placed were installation happens in debian/rules,
+rather than where build would normally be called.
+
+=item B<installcheck> [I<src-dir>] [I<build-dir>] [I<package-pattern>]
+
+Use B<pg_virtualenv make installcheck> to run the extension regression tests.
+This is meant to be run from C<debian/tests/control> using B<autopkgtest>. If
+I<build-dir> is omitted, the top source directory is used.
+
+If I<package-pattern> is given, options are passed to B<pg_virtualenv> to set
+up the temporary PostgreSQL instance to find extension files in
+C<debian/package-directory/>.
+
+Other than the other actions which run on the "supported" versions, if C<debian/control.in> exists, this one
+runs on the "installed" versions as reported by B<installed-versions> (unless
+I<package-pattern> is provided, which means we are called during a build).
+
+=item B<psql> [I<src-dir>] [I<build-dir>] [I<package-pattern>]
+
+=item B<virtualenv> [I<src-dir>] [I<build-dir>] [I<package-pattern>]
+
+Like B<installcheck>, but invokes B<psql>, or a shell, both wrapped in
+B<pg_virtualenv>. Input is read from stdin.
+
+=back
+
+Sometimes it is desirable to run extra code per version before invoking the
+action, in that case the loop over supported versions needs to be in the
+calling script. To facilitate this mode, actions can also be called as
+I<action>B<->I<version>. See the installcheck example below.
+
+=head1 SUPPORTED VERSIONS
+
+B<pg_buildext> reads C<debian/pgversions> to decide which PostgreSQL to build
+modules/extensions for. This file contains one PostgreSQL version number per
+line, in the following formats:
+
+=over 4
+
+=item B<all>
+
+Support all versions. This is recommended unless there are known incompatibilities.
+
+=item I<NN>
+
+Support this version.
+
+=item I<NN>B<+>
+
+Support this and all greater versions.
+
+=item B<#>I<...>
+
+Comment.
+
+=back
+
+For a version to be used, it must also be listed in the output of
+C</usr/share/postgresql-common/supported-versions>. See this file for how to
+configure the list of supported versions on your system.
+
+=head1 EXAMPLE
+
+=over 4
+
+=item B<debian/control.in:>
+
+  Source: postgresql-foobar
+  Rules-Requires-Root: no
+  Build-Depends:
+   debhelper,
+   postgresql-all <!nocheck>,
+   postgresql-server-dev-all (>= 217~),
+
+  Package: postgresql-PGVERSION-foobar
+  Architecture: any
+  Depends:
+   ${misc:Depends},
+   ${postgresql:Depends},
+   ${shlibs:Depends},
+
+=item B<debian/pgversions:>
+
+  all
+
+  # alternatives:
+  #9.6
+  #11+
+
+=item B<debian/rules> using B<dh $@ --with pgxs>:
+
+  #!/usr/bin/make -f
+
+  override_dh_installdocs:
+	  dh_installdocs --all README.*
+
+  %:
+	  dh $@ --with pgxs
+
+=item If the package does no support building from subdirectories, use B<dh $@ --with pgxs_loop>:
+
+  #!/usr/bin/make -f
+
+  %:
+	  dh $@ --with pgxs_loop
+
+=item If the package does not use PGXS's "make installcheck" for testing:
+
+  override_dh_pgxs_test:
+
+=item B<debian/rules> using B<pg_buildext> directly:
+
+  #!/usr/bin/make -f
+
+  include /usr/share/postgresql-common/pgxs_debian_control.mk
+
+  # omit this if the package does not use autoconf
+  override_dh_auto_configure:
+	  +pg_buildext configure build-%v "--libdir=/usr/lib/postgresql/%v/lib --datadir=/usr/share/postgresql-%v-foobar"
+
+  override_dh_auto_build:
+	  +pg_buildext build build-%v
+
+  override_dh_auto_test:
+	  # nothing to do here, see debian/tests/* instead
+
+  override_dh_auto_install:
+	  +pg_buildext install build-%v postgresql-%v-foobar
+
+  override_dh_installdocs:
+	  dh_installdocs --all README.*
+
+  override_dh_auto_clean:
+	  +pg_buildext clean build-%v
+
+  %:
+	  dh $@
+
+=item B<debian/tests/control:>
+
+  Depends: @, postgresql-server-dev-all
+  Tests: installcheck
+  Restrictions: allow-stderr
+
+=item B<debian/tests/control.in:> (optional)
+
+  Depends: @, postgresql-contrib-PGVERSION, postgresql-PGVERSION-bar
+  Tests: installcheck
+  Restrictions: allow-stderr
+
+=item B<debian/tests/installcheck:>
+
+  #!/bin/sh
+  pg_buildext installcheck
+  # alternatively: pg_buildext installcheck build-%v
+
+  # Running extra code before invoking the actual action:
+  set -e
+  for v in $(pg_buildext installed-versions); do
+	  test -L build-$v/sql || ln -s ../sql build-$v/
+	  test -L build-$v/expected || ln -s ../expected build-$v/
+	  pg_buildext installcheck-$v build-$v
+  done
+
+=back
+
+=head1 SOURCE DIRECTORY
+
+If the package source code is not in the top level directory (i.e. the directory
+which has C<debian/> as subdirectory), use the I<src-dir> argument, where
+I<src-dir> must be an absolute path. Example:
+
+  override_dh_auto_build:
+	  +pg_buildext build $(CURDIR)/postgresql-module build-%v
+
+=head1 COMPATIBILITY
+
+B<pg_buildext loop> was introduced in postgresql-server-dev-all (>= 141~).
+
+The usage of "all" or "NN+" in debian/pgversions was introduced in
+postgresql-server-dev-all (>= 148~).
+
+B<pg_buildext installcheck> was introduced in postgresql-server-dev-all (>=
+153~).
+
+B<PG_VIRTUALENV_UNSHARE=-n> was introduced in postgresql-common (>= 170~).
+
+Handling of C<debian/tests/control.in> with B<PGVERSION> replacement was
+introduced in postgresql-common (>= 171~).
+
+The action B<installed-versions> was introduced in postgresql-common (>= 208~).
+B<installcheck> was switched to use it in the same version.
+
+B<dh $@ --with pgxs> and B<pgxs_loop>, the corresponding B<--buildsystem>, and
+the B<psql> and B<virtualenv> actions were introduced in postgresql-server-dev-all (>= 217~).
+
+=head1 SEE ALSO
+
+C</usr/share/postgresql-common/supported-versions>, autopkgtest(1),
+pg_virtualenv(1).
+
+=head1 AUTHORS
+
+Dimitri Fontaine L<E<lt>dim@tapoueh.orgE<gt>>, with extensions by
+Christoph Berg L<E<lt>myon@debian.orgE<gt>>.