update the notes on FS#1843

doc/FS1843.md

@@ -24,8 +24,8 @@ 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.
-Ports exhibiting no version differences between the repos and /var/lib/pkg/db
-would be left alone, unless forceRebuild was requested.
+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
@@ -33,14 +33,16 @@ 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 calcDependencies()
+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.
+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 calcDependencies(), the 
-contents of this list were not being included in the post-transaction 
+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
@@ -48,25 +50,43 @@ 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.
+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)".
 
-As for teodor's request to unify into one list the post-transaction summary
-of missing ports and already-up-to-date ports, I think the possible benefits
-for easier parsing are overstated. Some users might not want the two lists
-mixed together, for instance when the dependency tree of a valid target ends
-up drowning out all the ports that are not in the repos. Two separate lists
-would offer greater readability in most cases.
+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:", suggests a new way for the softdeps branch to
-handle FS#1910. All arguments to ``install`` and ``depinst`` will be tested 
+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. Then, if any of the requested ports is not yet
+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. This approach will give users at
-least partial results from a malformed command, while also providing an
-informative message so that a revised command can be issued later.
+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.