prt-get/doc/FS1843.md

# Flyspray 1843 notes
## Was: Re: Please make the output of prt-get --test more common

teodor observed that prt-get --test gives two different styles of output.
The output style was found to be affected by the number of packages requested 
on the command line (one versus many), and by whether dependency resolution 
was toggled (install versus depinst).

In the case when one package was requested for installation, an early check 
of /var/lib/pkg/db for the existence of a previous installation would alert the
user to the malformed command. No such check of /var/lib/pkg/db was
being performed for multiple packages passed on the command line (FS#1910), and
so the program continued all the way through executeTransaction() and
evaluateResult(), which produced the more verbose output that teodor noted.

A similar discrepancy could be observed when requesting an **update** of **one** 
package that was not previously installed, versus an update of **multiple**
packages among which there are some not yet installed. You would have seen a
terse warning in the first case, and a more verbose output in the second case.

The softdeps branch in this code base is now more consistent in performing the 
scan of /var/lib/pkg/db, no matter how many packages are passed as argument. 
But the mixed-upinst branch collapses the distinction between install and 
update, always bringing up to date all the ports passed as argument (and their
dependencies, unless --nodeps is given), so it can postpone the scan of
/var/lib/pkg/db until the step of customizing pkgadd flags for each target.
Hence there is no corresponding code in the mixed-upinst branch to solve FS#1910 
by exiting early with an error message.

teodor's second observation is more interesting. During dependency resolution, 
the invalid arguments (ports not found in the active repos) were silently being
dropped, rather than being kept in memory for a post-transaction report. If
**all** ports passed to a ``depinst`` command are nowhere among the active
repositories, then the empty set is what gets used for executeTransaction(),
with the predictable result "no package specified for install". Why did we see
a different result when running ``install``? Because the calculateDependencies()
method was never called, and so executeTransaction() received the entire list 
of nowhere-to-be-found ports! Iterating through this list of nonexistent ports
would populate the missingPackages list, which would then be displayed nicely 
during the post-transaction summary. This side-effect of toggling dependency
resolution could be observed in both the softdeps and the mixed-upinst branch,
prior to the commits of 2023-09-15.

Although we do populate a missingPackages list during calculateDependencies(), 
the contents of this list were not being included in the post-transaction 
summary. As the code was originally conceived, executeTransaction() would get
a filtered list, with missing packages omitted. This side-effect of ``depinst``
violates the principle of least surprise, because users like teodor might
justifiably expect toggling dependency resolution to generate a superset of
**their argument list** @ARGV, not just a superset of the valid ports in @ARGV.
To be more faithful to the principle of least surprise, the softdeps branch now 
propagates into executeTransaction() even the ports that are not in the repos, 
so that the post-transaction summary can display them. The mixed-upinst branch
does the same, but because it merges ``install`` and ``update``, any requested
targets that are already installed and up-to-date will appear in the
post-transaction summary under the header "Packages already installed before
this run (ignored)".

With dependency resolution enabled, the list of "Packages already installed
before this run (ignored)" often fills up the entire height of a terminal.
If we implemented teodor's suggestion and united the list of
"Packages not found" with this list --- already often big enough on its own ---
then readability of the post-transaction summary would suffer.
Two separate lists would offer greater readability in most cases, both for
the human eye and for a shell script.

teodor's proposed heading for a united list, "The following ports were 
not found/already installed:", did inspire a new way for the softdeps branch
to handle FS#1910. All arguments to ``install`` and ``depinst`` will be tested 
against /var/lib/pkg/db to ensure that they're not already installed, and if 
all the tests fail then the user is immediately alerted to the malformed 
command. This preliminary check is simply jw's original design, but extended 
from one port to many. However, if any of the requested ports is not yet
installed, we can go ahead with initRepo() and attempt a less ambitious
transaction (limited to a subset of the user's argument list). The program
will reach evaluateTransaction() and display what succeeded, as well as what 
was wrong with the original command.

The softdeps branch has no corresponding leniency in handling an ``update`` 
command, because the typical scenario for using that command is after 
running ``prt-get diff``, at which point the user can be expected to know 
what's on their system and to pass as arguments only the names of packages 
already installed. So the early exit behaviour of my previous solution to
FS#1910 is retained for the ``update`` command. But it's easy to imagine a
user passing invalid targets to an ``install`` command, in the absence of
any cues from running ``prt-get listinst | grep -E 
(package1|package2|...|packageN)``, and to handle that possibility it
makes sense to parse leniently the arguments passed to ``install``. Users
then obtain on the first try, most of what they intended, while also getting
an informative list of already-installed packages in the post-transaction report.
If they really intended to force the rebuild of those already-installed
packages, they can issue a revised command after the first command succeeds.