#+TITLE: Installing applications under =$HOME=

One day I woke up and decided to stop letting ~make install~ put
programs under =/usr/local/=.  Not every project provides an
=uninstall= target, so over time, as more and more applications get
lumped under that hierarchy, it becomes a clutter of stuff that I
cannot remove without…

1. guesstimating what files belong to any given program using
   timestamps,
2. weighing my odds of passing correctly crafted globs to the likes of
   =sudo find -delete= and =sudo rm -r= without destroying my system.

Instead I figured I would start ~./configure~'ing programs with
=--prefix=${HOME}/apps/${program}=, and teach whichever dotfiles
manage session environment variables to arrange for installed
resources to be found.

How hard could it be?

* =PATH=
The Correct Way™ to set environment variables seems to depend on

1. the kind of session (TTY vs GUI),
2. the init system (e.g. [[https://www.freedesktop.org/software/systemd/man/environment.d.html][systemd user environment variables]])
3. the desktop environment (e.g. [[https://userbase.kde.org/Session_Environment_Variables][Plasma session environment variables]]),
4. the display server,
5. the distro?
   - e.g. Debian's SSDM [[https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=794419][used not to]] source =~/.profile=,
   - and [[https://github.com/sddm/sddm/issues/448][developers said]] it should not anyway,
   - except [[https://github.com/sddm/sddm/issues/1551][it has provisions to do so]]?
6. [[https://man7.org/linux/man-pages/man8/pam_env.8.html][PAM]]?

Empirically with Plasma on both Tumbleweed (20230929) and Debian 12,
=~/.profile= seems to be run for both TTY and GUI sessions.  Unclear
what arcane magic is causing that: probably the login manager - on
Tumbleweed =/usr/share/sddm/scripts/Xsession= seems to start a ~bash
--login~, but getting lost in the =/usr/etc/X11/xdm/= weeds trying to
track down who might source that =Xesssion= script.

=~/.profile= it is, then 🤞

(For other DEs on X, my recollection was that =~/.xsessionrc= is the
way to go for GUI sessions?  No clue about Wayland)

* ~man~ pages
=manpath(5)= says:

#+begin_quote
By default, man-db examines the user's =$PATH=.  For each
=path_element= found there, it adds =manpath_element= to the search
path.

If there is no =MANPATH_MAP= line in the configuration file for a
given =path_element=, then it adds all of =path_element/../man=,
=path_element/man=, =path_element/../share=man=, and
=path_element/shared/=man= that exist as directories to the search
path.
#+end_quote

How convenient!  Setting =PATH= automatically takes care of ~man~
then… unless =MANPATH= is set, in which case that logic is bypassed.

** openSUSE
=/usr/etc/profile.d/manpath.sh= [fn:: sourced by =/etc/profile=,
sourced by =/usr/etc/profile= and =~/.profile=.] plays a little danse
to (a) query ~manpath~, which runs the heuristic described above (b)
set the resulting value "in stone" by exporting =MANPATH=.

This means that ~man~ will not consider any =PATH= element added by
the user after that profile fragment was sourced.

Solutions:

1. Unset =MANPATH= in =~/.profile=, after =/etc/profile= is read.
   =~/.profile= is "read each time a login shell is strated.  All
   other interactive shells will only read .bashrc", so unclear
   whether that will affect graphical sessions.
2. Extend =PATH= with apps /before/ those profile fragments are
   loaded.  Unclear how to accomplish that:
   - [[https://wiki.archlinux.org/title/environment_variables#Per_user][systemd user environment variables]]?  Seems to be limited to
     =KEY=VALUE= directives; I would like to run a bit of logic that
     will automatically add every =~/apps/*/bin= directory.
   - [[https://userbase.kde.org/Session_Environment_Variables][Plasma session environment variables]]?  Presumably will not affect
     TTYs?
3. Embrace the distro's method: if =MANPATH= is set, extend it.

Went with solution 1 because empirically =~/.profile= seems to be
sourced for GUI sessions (as noted in § =PATH=).

* ~info~ pages
Similar to ~man~, ~info~ knows to work with =PATH=.  The priority
[[https://git.savannah.gnu.org/cgit/texinfo.git/tree/info/infopath.c?h=texinfo-7.0.3#n41][seems to be]]:

1. the =INFOPATH= environment variable,
2. the =INFODIR= build macro, /if =infopath-no-defaults= is not set/,
3. the =DEFAULT_INFOPATH= build macro, /if =INFOPATH= is unset or ends
   with a trailing colon/.

Any of these can contain the =PATH= literal, which means "iterate over
=${PATH}= and add nearby =share/info= & =info= directories".  By
default, =DEFAULT_INFOPATH= contains =PATH= 🥳 but =INFODIR= has
priority and is set to something boring like =/usr/share/info= 😒

Solution:

#+begin_src bash
cat <<EOF > ~/.infokey
#var
# Disable INFODIR; fall back to DEFAULT_INFOPATH which prioritizes
# program PATH over /usr/share/info.
infopath-no-defaults=On
EOF
#+end_src

* TODO ~bash~ completions

* TODO Desktop entry files
Prepend =${HOME}/apps/${program}/share= to =XDG_DATA_DIRS=?

* TODO systemd services
See systemd.unit(5)

* Putting it all together
Presenting =~/apps/activate=, to be sourced from =~/.profile=:

#+begin_src bash
# Hey Emacs; this is a -*- shell-script -*-.
# Hopefully invoked by bash 🤞

_apps_dir=$(dirname ${BASH_SOURCE})

_apps_PATH=$(
    shopt -s nullglob
    bins=( "${_apps_dir}"/*/bin )
    IFS=: eval 'echo "${bins[*]}"'
)

export PATH=${_apps_PATH}:${PATH}
#+end_src

* Resources
** [[https://nullprogram.com/blog/2017/06/19/][nullprogram.com]] — Building and Installing Software in $HOME
Explains how to set things up so that one can use =~/.local= as a
first-class citizen for applications, libraries and development
resources (headers, pkg-config, manpages).