[gentoo-dev-announce] Introducing python-exec:2 (and the migration plan)

[gentoo-dev-announce] Introducing python-exec:2 (and the migration plan)

[Michał Górny]

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Hello, all.

I have committed today the eclass support code for python-exec:2,
and first package.mask-ed version of it. The benefits of the new
solution were explained in the earlier RFC mail [1]. Now for
the migration plan.

The eclasses cleanly support either version of the wrapper. They use :=
dep and a has_version check to use the latest slot installed. That is,
you won't get the new behavior until you install python-exec:2.
Afterwards, the packages should cleanly switch on next rebuild.

We're planning on keeping python-exec:2 in package.mask for a while
for testing, then unleash it to the ~arch population. When tested well
enough, we will stabilize it and start deprecating the old wrapper. For
most of our users, this process should be seamless and pain-free.

However, we know of some ebuilds that are going to be broken with
the new wrapper since they rely too much on wrapping mechanism [2].
Since many of those can't really be fixed much better, those ebuilds
will be 'locked' at a single version of the wrapper.

If you know that a package does not work with python-exec:2,
the following snippet needs to be added to it:

    DEPEND="dev-python/python-exec:0"
    _PYTHON_WANT_PYTHON_EXEC2=0

This will ensure keeping the old wrapper around and override
the has_version check to force using the old wrapper.

If you know that your package works only with python-exec:2,
use the following snippet instead:

    DEPEND="dev-python/python-exec:2"

No override is necessary here, since install of new wrapper will cause
the eclass to automatically switch to it. But please note that your
package's visibility/keywords will need to follow python-exec:2.

All testing will be appreciated. Enjoy.

[1]:http://thread.gmane.org/gmane.linux.gentoo.devel/88095
[2]:https://bugs.gentoo.org/show_bug.cgi?id=484398

-- 
Best regards,
Michał Górny

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