[pacman-dev] IgnorePkg for specific package versions

[Daniel Schoepe]

Hi everyone,

I think that it would be nice to be able to specify particular version
constraints for packages to be ignored in IgnorePkg / --ignore, like it
was suggested on the forums [1]. This would be helpful for preventing
particular buggy versions from being installed but trying each update
after that.

Regarding the comment that partial upgrades are not supported: This is
"invariant" is already being broken by having IgnorePkg in the first
place, so I don't think this proposal makes it worse.

It turns out that this is *almost* very easy to implement by converting
each element of handle->ignorepkg to an alpm_depend_t and then comparing
with _alpm_dec_literal(). However, this does not quite work since some
ignore-checks also check if the local package matches the ignore rule,
which leads to arguably counter-intuitive results when used with lower
bounds:

If package-0.1-1 is installed and package-0.2-1 has a bug, a user might
write package<=0.2-1 in IgnorePkg, but this leads to the package never
being upgrade anymore since the local version (0.1-1) matches this
condition.

So I have a couple of questions: Do you think this is a sensible feature
to have in the first place? If so, how should the potential problem
above be handled? These are the most reasonable options that I could
come up with:

1. Don't compare with the local version anymore: This has the downside
of altering the semantics of IgnorePkg even if the user does not change
their config.

2. Implement the less intuitive semantics that would result from 
my suggested change. This is not so nice since a common use case might
be to wait until a particular version that fixes some bug is
released. A new package release of the same version would usually not
help then.

3. Restrict the syntax to only allow equality comparisons in
IgnorePkg. This prevents the use case from 2 as well.

4. Do not compare with the old version if and only if a version
constraint is given on for this package. This has the advantage of not
affecting anybody using IgnorePkg at the moment and anyone using version
constraints can be made aware of this behaviour. However, this is
somewhat ad-hoc and asymmetric.

Any comments and input is appreciated.

Cheers,
Daniel

[1] https://bbs.archlinux.org/viewtopic.php?id=182893
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