Re: [PATCH makewhatis] add NIXSTOREDIR configuration variable to support NixOS

[Ingo Schwarze <schwarze@usta.de>]

Hi Lukas,

Earendil wrote on Tue, Mar 30, 2021 at 09:49:49PM +0200:

> On NixOS there is a similar situation as with Hombrew: The actual
> man pages are installed into custom prefixes for each package under
> /nix/store and then symlinked to in the global share/man directory
> (which is /run/current-system/sw/share/man for NixOS). This of course
> makes makewhatis skip every installed man page when indexing because
> /nix/store is considered outside of the man directory.

Uh oh.  I must admit i found this "cellar" concept so weird and unusual
that i didn't anticipate any other system doing anything similar, and
hence the overly specific naming of the feature.  Then again, if i
read the commit logs correctly, it did take six years until the second
system (among about two dozen being actively maintained) turned up that
uses such a method...

> To fix this issue I've followed the implementation of HOMEBREWDIR. The
> drawback of this being that more or less the same code is duplicated for
> this purpose. However there may be a (arguably very small) group of
> users who would possibly want to use both configuration variables at the
> same time as the nix package manager can also be installed on macOS, but
> it would probably also not do any harm merging the two variables into one.

Indeed.  Using two package managers on the same machine at the same
time is no doubt a recipe for disaster, and i expect getting the
manual pages indexed will be the least of your worries...

So i'm not really convinced having *two* such variables with identical
functionality makes anything better.

Would simply setting HOMEBREWDIR=/nix/store be OK with you?

We could of course rename the variable to something more generic,
*if* a generic name for this concepts exists or can be invented
in a reasonable way.

> This patch is necessary to provide a mandoc-based alternative to the
> current documentation.man module in NixOS which uses GNU's man-db
> package. I have a working implementation of this (using a cvs version of
> mandoc with this patch applied) here:

Nice.   :-)

> https://github.com/openlab-aux/vuizvui/blob/master/modules/user/sternenseemann/documentation/mandoc.nix

To speed up the reply - i caused enough delay already - i refrained from
studying your code so far.

> A side note: During testing I haven't been able to trigger the code path
> of the ifdef in filescan. I've added it anyways because HOMEBREWDIR also
> has been added there, but didn't seem to be a situation where basedir is
> set and filescan is called, but maybe I missed something.

To reach the filescan() function, you need to call makewhatis with
the -d, -u, or -t option.

Unless i misunderstand my own code (after it required little maintenance
effort for a number of years), using -d or -u will indeed frst call
set_basedir() and then filescan() shortly afterwards, see the
function mandocdb() in the file mandocdb.c.

Yours,
  Ingo
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