[Portage][] is [[Gentoo]]'s default package manager.  This post isn't
supposed to be a tutorial, the [handbook][] does a pretty good job of
that already.  I'm just recording a few tricks so I don't forget them.

User patches
============

While playing around with [[LDAP]], I was trying to troubleshoot the
`SASL_NOCANON` handling.  “Gee,” I thought, “wouldn't it be nice to be
able to add debugging printfs to figure out what was happening?”
Unfortunately, I had trouble getting `ldapwhoami` working when I
compiled it by hand.  “Grrr,” I though, “I just want to add a simple
patch and do whatever the ebuild already does.”  This is actually
pretty easy to do, once you're looking in the right places.

Write your patch
----------------

I'm not going to cover that here.

Place your patch where `epatch_user` will find it
-------------------------------------------------

This would be under

    /etc/portage/patches/<CATEGORY>/<PF|P|PN>/

If your ebuild already calls `epatch_user`, or it uses an eclass like
`base` that calls `epatch_user` internally, you're done.  If not, read
on…

Forcing `epatch_user`
---------------------

While you could always write an [[overlay|Gentoo_overlay]] with an
improved ebuild, a quicker fix for this kind of hack is
[/etc/portage/bashrc][bashrc].  I used:

    if [ "${EBUILD_PHASE}" == "prepare" ]; then
        echo ":: Calling epatch_user";
        pushd "${S}"
        epatch_user
        popd
    fi

to insert my patches at the beginning of the `prepare` phase.

Cleaning up
-----------

It's safe to call `epatch_user` multiple times, so you can leave this
setup in place if you like.  However, you might run into problems [if
you touch autoconf files][autoconf], so you may want to move your
`bashrc` somewhere else until you need it again!


[Portage]: http://www.gentoo.org/proj/en/portage/index.xml
[handbook]: http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=1
[bashrc]: http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=3&chap=6#doc_chap3
[autoconf]: http://comments.gmane.org/gmane.linux.gentoo.devel/76466

[[!tag tags/tools]]
[[!tag tags/programming]]