[gentoo-dev] [PATCHES] python-r1, add integrity checks for redefined control vars

[Michał Górny]

Hi,

Here's a patch serie inspired by the recent spidermonkey issue [1]. Long
story short, both mozcoreconf-*.eclass and spidermonkey were setting
different values of PYTHON_REQ_USE and inherit python-any-r1. Thanks to
double include guards, the dependencies were set using the first value
on the first iteration. However, python_setup() used the final value,
being more strict as a result.

This patch series aims to reduce the likeliness of such mistakes,
by comparing the values of output variables between successive eclass
inherits. This both catches some mistakes of overwriting the value,
and any potential integrity issues in eclass itself.

The remaining commits are purely cleanup/refactor.

However, the following technical limitations need to be noted:

1. We can only detect changes of control variables between successive
inherits of eclass, which makes every solution highly dependent
on the inherit order. If you 'inherit mozcoreconf-v4 python-any-r1',
the control variables are overwritten before python-any-r1 can see them.

2. There was a suggestion to make the eclass output variables updated
for the last values of control. However, the output variables are
currently marked readonly, to avoid accidental rewrites. If we were
to update them, we would have to disable that.

3. The same bugs (and also the case of defining after inherit) could
be caught if control variables were made readonly after setting globals.
However, this would cause spurious errors if the ebuild was sourced
more than once by the PM.

Please review.

[1]:https://bugs.gentoo.org/611176

--
Best regards,
Michał Górny