[pacman-dev] Cleaning up pretty printing in pacman.

[Simon Gomizelj]

While diving into pacman's output code to try and add colours I've
noticed that pacman's pretty printing code is somewhat awkward. Its very
clear its grow organically without ever really being cleaned up.

- Translation messages shouldn't have formatting information embedded
  into them:

    _("Name"),    not _("Name           :")
    _("Version"), not _("Version        :")
    etc

- Pacman puts a lot of effort into making some parts of its output is
  nicely aligned, while other parts don't and expects padding to be
  hardcoded. Pacman should do _all_ the aligning.

An example of where pacman's pretty printing code is specifically
inefficient... dump_pkg_full:

    cols = getcols(fileno(stdout));

    string_display(_("Name           :"), alpm_pkg_get_name(pkg), cols);
    string_display(_("Version        :"), alpm_pkg_get_version(pkg), cols);
    string_display(_("Description    :"), alpm_pkg_get_desc(pkg), cols);
    string_display(_("Architecture   :"), alpm_pkg_get_arch(pkg), cols);
    string_display(_("URL            :"), alpm_pkg_get_url(pkg), cols);
    list_display(_("Licenses       :"), alpm_pkg_get_licenses(pkg), cols);
    list_display(_("Groups         :"), alpm_pkg_get_groups(pkg), cols);
    deplist_display(_("Provides       :"), alpm_pkg_get_provides(pkg), cols);
    deplist_display(_("Depends On     :"), alpm_pkg_get_depends(pkg), cols);

- cols is recalculated for each package.
- string_display,list_display,etc call string_length on $1 each time.

These two numbers could basically be considered constants though through
the outputting. So this means when I do `pacman -Si` (output for ~6080
packages here):

- cols is recalculated ~6080 times too much.
- string_display about (6080 * 20) or 121600 times.

dump_pkg_full is basically outputting a table. There is no reason pacman
couldn't pre-calculate the dimensions of the table to significantly
reduce the amount of work it does when printing each row.

Furthermore, there seems to be, with my colour patches, two more
independent table implementations: table_display and
add_table_row/display_transaction_sizes. They all build the same kind of
table and format them in similar ways.

I think the right way forward is to add a nice table formatter library
to pacman that can be reused for everything. I whipped up a very quick
prototype as a proof of concept: http://ix.io/4CP/

I wanted to bring this up so that a) its on the record and b) we can
start talking about if/how to implement this. I'm willing to put in the
effort to get this through.