tree-wide: alternatives support for pacman

[robertkirkman]

• The update-alternatives tool can also be used by pacman-based Termux installations, and is necessary for convenient management of some symbolic links, like $PREFIX/bin/pager, so split from dpkg into a subpackage that pacman can depend on the same way that apt-based bootstraps pull in update-alternatives
• This block is frequently found as necessary among packages that have a postinst script:

if [ "$TERMUX_PACKAGE_FORMAT" = "pacman" ]; then
	echo "post_install" > postupg
fi

• The reason this block is necessary is because otherwise, when upgrading packages using pacman, if the package was already previously installed (an "upgrade" situation), unlike apt, pacman does not actually run its post_install script function by default, only its post_upgrade script function.

• I noticed that to avoid repetitively pasting it into many packages, it seems reasonable to globally include this check and override in termux_step_create_pacman_install_hook().

• postupg is not used for anything else anywhere in Termux except for termux-pacman. Therefore, it seems safe to universally override post_upgrade() with post_install() in pacman packages anytime a postupg script that does something other than post_install doesn't actually exist in Termux (no such script currently exists, but could in the future) and a post_install script function has already been created (implying that a postinst script existed and has just been converted into a post_install function in the pacman .INSTALL file)

[robertkirkman]

I have now actually tested this on a termux-pacman device.

• as expected, update-alternatives seems to correctly work independently on its own on a termux-pacman device where dpkg isn't installed at all

• However, I noticed that even after update-alternatives has been installed, on termux-pacman, the preexisting .INSTALL scripts for pacman to run update-alternatives wouldn't actually run whenever I installed the packages.

  • I noticed that was because the necessary echo "post_install" > postupg command has not been getting run in many places, so I moved all instances of echo "post_install" > postupg into a single global location that can hopefully propagate it more reliably.
  • It is necessary to revision-bump many packages after applying the global equivalent of echo "post_install" > postupg appropriately, to signal to the termux-pacman CI to rebuild and redeploy these packages with corrected pacman .INSTALL files

I have added commits with all the additional changes that were necessary for the update-alternatives system to begin working when I test it on the termux-pacman device.

~ $ pacman -U ./nano-8.5-3-arm.pkg.tar.xz 
loading packages...
resolving dependencies...
looking for conflicting packages...

Packages (1) nano-8.5-3

Total Installed Size:  0.58 MiB

:: Proceed with installation? [Y/n] 
(1/1) checking keys in keyring                                        [######################################] 100%
(1/1) checking package integrity                                      [######################################] 100%
(1/1) loading package files                                           [######################################] 100%
(1/1) checking for file conflicts                                     [######################################] 100%
(1/1) checking available disk space                                   [######################################] 100%
:: Processing package changes...
(1/1) installing nano                                                 [######################################] 100%
update-alternatives: using /data/data/com.termux/files/usr/bin/nano to provide /data/data/com.termux/files/usr/bin/editor (editor) in auto mode
:: Running post-transaction hooks...
(1/1) Creating the whatis database...
~ $ readlink -f $(command -v editor)
/data/data/com.termux/files/usr/bin/nano
~ $ 

[robertkirkman]

The error says that the checksum of the zrok source download is invalid. I will look later to find out why the checksum is invalid and what should be done.

[robertkirkman]

All the packages that need to be rebuilt couldn't be built within 6 hours, so there will need to be a second PR later to revision-bump the remaining packages.

I also had to change the checksum of zrok. Unfortunately, I don't know why the checksum of zrok has changed. I would be relieved if someone knows why that happened.

[TomJo2000]

All the packages that need to be rebuilt couldn't be built within 6 hours, so there will need to be a second PR later to revision-bump the remaining packages.

I also had to change the checksum of zrok. Unfortunately, I don't know why the checksum of zrok has changed. I would be relieved if someone knows why that happened.

zrok will occasionally do retags of their latest releases, it's an annoying tendency.

[robertkirkman]

If accepted, this PR + the follow-up revision-bumps would solve this error that currently happens in default termux-pacman after installing git:

~ $ mkdir test1
~ $ cd test1
~/test1 $ touch file
~/test1 $ git add file
~/test1 $ git commit
hint: Waiting for your editor to close the file... error: cannot run editor: No such file or directory
error: unable to start editor 'editor'
Please supply the message using either -m or -F option.
~/test1 $ 

(explanation: the editor symlink is now the default editor of git for termux-apt, so termux-pacman has desynchronized from the configuration of termux-apt with regard to the default editor for many programs)

termux-packages/packages/git/build.sh

Lines 34 to 35 in c8e204d

	DEFAULT_PAGER=pager
	DEFAULT_EDITOR=editor

[robertkirkman]

I have realized that unfortunately, installing update-alternatives into termux-pacman would create a folder named /data/data/com.termux/files/usr/var/lib/dpkg/alternatives. While it would still work because update-alternatives works independently from dpkg, the presence of a folder named dpkg in non-dpkg Termux would compromise the idea of alternative package manager in Termux, so it is best to implement this in termux-pacman a different way.