[PATCH setup] Handle '--packages package=version'

[David Allsopp]

Jon Turney wrote:
> Handle '--packages package=version' to allow specifing the version of a
> package to install on the command line.
> 
> isManuallyWanted() now returns the target packageversion (if specified),
> or an empty packageversion (which is translated into an instruction to
> the solver to choose the version).
> 
> In the 'upgrade' case, this changes from using the complex logic of
> packagemeta::trustp() to determine the target version, when unspecified
> on the command line, to allowing the solver to make that decision (which
> should be broadly the same i.e. not downgrading test versions, etc.).
> 
> This also subtly changes the behaviour when the package version is not
> specified.  Instead of forcing the current version, we allow the solver
> to choose the version, so it may not pick that version, if other
> constraints exist, which prevent a solution containing that version.
> 
> There's probably some future work which can be done to simplify the
> remaining uses packagemeta::trustp(), which are only related to the UI.

<snip>

This is really useful (tested locally for a couple of use-cases: one wanting
a downgrade from latest and the other to manually specify a test version).

Does libsolv give the ability to put more complex constraints? In opam, for
example, I can issue `opam install 'utop<2.7.0' and get the last version
before 2.7.0.

`--packages mingw64-x86_64-binutils=2.35.2-1` is already very useful but
`--packages mingw64-x86_64-binutils<2.36` is even more so.



David