Re: Package API compatibility and guix package variable names

[Andreas Enge <andreas@enge.fr>]

Hello,

just replying to part of your message, since I think there might be a
misunderstanding:

On Wed, Jul 27, 2016 at 11:06:15PM +0200, Danny Milosavljevic wrote:
> Just to make sure: I'm not saying the API major number should absolutely be part of the name, I'm saying there should be version bounds for all the inputs of packages.

The inputs of our packages are absolutely precise: They are given as scheme
variables (which are, in a sense, a moving target, since their content
changes over time; but they are completely fixed at any given point in time).
So we have no way of saying, like in many other distributions, that the input
is any "python >= 2 and < 3"; in fact, we are always saying "use exactly
this Python, with this source, build system, inputs, etc.".

If a package x has as input "python", this is the scheme variable of this name,
which, in my current git tree, refers to a package containing Python 3.4.3,
and nothing else. Another package y may have as input "python-2", which is a
scheme variable containing currently Python 2.7.10. In core-updates, we
updated python-2 to contain Python 2.7.11. So the input to package y,
compiled in core-updates, is still called "python-2", but has actually
changed. The variable names are just conventions; and it is almost a pure
coincidence that they usually are the same as the "name" field of the
package record :-)

But maybe I simply misunderstood your comment. Anyway, upgrading has been
working generally well so far. Also, it is not always easy to determine
whether APIs are compatible or not, since they are not necessarily tied
to major versions of the software. For instance, I think that anything
(or almost) written for gmp-4 still compiles with gmp-5 or 6. But this
requires some familiarity with the code, which I have in this case since
I am following the gmp development. Apart from that, we have thousands of
packages now, some of which are probably not familiar to anybody. I know
that I packaged software of which I did not even understand the description,
just because it was a prerequisite for something I am interested in...

Andreas