Newbie: What's the importance of *.drv, *.-builder, etc. files in /gnu/store?

[Rodrigo Morales]

Table of Contents
_________________

1. TL; DR
2. The context
3. The question


1 TL; DR
========

  I'm a newbie when it comes to understanding the file extensions of
  files that exist in `/gnu/store'. I want to know what each file
  extension means and how they are important to the operating system or
  for the user. Namely, the extensions that I don't understand yet are +
  `*.drv', `*-builder', `*.tar.xz.drv.', `*.tar.xz-builder.' and +
  `*-honor-localdir.patch'. References to the manual or documentation on
  this topic are greatly appreciated.


2 The context
=============

  Initially, my `/gnu/store' have no directory whose name contain the
  word `transmission'.

  ,----
  | find /gnu/store -mindepth 1 -maxdepth 1 -name '*transmission*' | wc -l
  `----

  ,----
  | 0
  `----

  Now, I install the package `transmission'.

  ,----
  | delta% guix package -i transmission
  | The following package will be installed:
  |    transmission 3.00
  |
  | 1.5 MB will be downloaded
  |  transmission-3.00  664KiB

 222KiB/s 00:03 ▕██████████████████▏ 100.0% transmission-3.00-gui  757KiB

                                     271KiB/s 00:03 ▕██████████████████▏
100.0%The following derivation will be built:
  |   /gnu/store/6x0f3mczkz5dmsrrnw5z6nwd2l0lnr33-profile.drv
  |
  | applying 27 grafts for transmission-3.00 ...
  | building profile with 11 packages...
  | delta% echo $?
  | 0
  `----

  After installing the package, there are 4 directories and 8 files in
  `/gnu/store'. See proof below.

  ,----
  | find /gnu/store -mindepth 1 -maxdepth 1 -name '*transmission*' | wc -l
  | find /gnu/store -mindepth 1 -maxdepth 1 -name '*transmission*' -printf
'%y %p\n'
  `----

  ,----
  | 12
  | f
/gnu/store/w5axm22g9nrgbkhrsjlf4zvnksavdjwp-transmission-3.00.tar.xz.drv
  | f
/gnu/store/d4h1gkavik552f9bqcnimiylhrp18b7c-transmission-honor-localedir.patch
  | f
/gnu/store/xivc36rv3dk5qzfmf78hzrrvnp6m1crv-transmission-3.00.tar.xz-builder
  | f
/gnu/store/01h9m5lrmxhcbxxlf45z24zgmbvm6ibj-transmission-3.00.tar.xz.drv
  | f /gnu/store/asq7m7221syq0rlwiy01lhcsj54lihyv-transmission-3.00-builder
  | f /gnu/store/v8sgmbxrji7gkd4pyc2x4wik4x29qysg-transmission-3.00.drv
  | f /gnu/store/dan5qy88nzdyn9010qz0a9666bss6x4v-transmission-3.00-builder
  | f /gnu/store/pv9yvk7qzs7ifx5fkam2mqla51y12ihh-transmission-3.00.drv
  | d /gnu/store/dxyjmmrw6vkbjmm4jx17i92rnc4mmcm3-transmission-3.00
  | d /gnu/store/p4wfwg0d6qz5navc6w5gnc6gzibhiisd-transmission-3.00-gui
  | d /gnu/store/6kmyb111bpf0mx25vd981h4zqmzp02jl-transmission-3.00-gui
  | d /gnu/store/pnq464qnrr5nrmhr3avn39b22axf1na8-transmission-3.00
  `----

  The last 4 directories in the output shown above look as if they
  contain the binaries and additional files of the build process. Please
  correct me if I'm wrong.

  ,----
  | echo -
  | find /gnu/store/p4wfwg0d6qz5navc6w5gnc6gzibhiisd-transmission-3.00-gui
-mindepth 1 -maxdepth 1
  | echo -
  | find /gnu/store/6kmyb111bpf0mx25vd981h4zqmzp02jl-transmission-3.00-gui
-mindepth 1 -maxdepth 1
  | echo -
  | find /gnu/store/dxyjmmrw6vkbjmm4jx17i92rnc4mmcm3-transmission-3.00
-mindepth 1 -maxdepth 1
  | echo -
  | find /gnu/store/pnq464qnrr5nrmhr3avn39b22axf1na8-transmission-3.00
-mindepth 1 -maxdepth 1
  `----

  ,----
  | -
  | /gnu/store/p4wfwg0d6qz5navc6w5gnc6gzibhiisd-transmission-3.00-gui/bin
  | /gnu/store/p4wfwg0d6qz5navc6w5gnc6gzibhiisd-transmission-3.00-gui/share
  | /gnu/store/p4wfwg0d6qz5navc6w5gnc6gzibhiisd-transmission-3.00-gui/etc
  | -
  | /gnu/store/6kmyb111bpf0mx25vd981h4zqmzp02jl-transmission-3.00-gui/bin
  | /gnu/store/6kmyb111bpf0mx25vd981h4zqmzp02jl-transmission-3.00-gui/share
  | /gnu/store/6kmyb111bpf0mx25vd981h4zqmzp02jl-transmission-3.00-gui/etc
  | -
  | /gnu/store/dxyjmmrw6vkbjmm4jx17i92rnc4mmcm3-transmission-3.00/bin
  | /gnu/store/dxyjmmrw6vkbjmm4jx17i92rnc4mmcm3-transmission-3.00/share
  | /gnu/store/dxyjmmrw6vkbjmm4jx17i92rnc4mmcm3-transmission-3.00/etc
  | /gnu/store/dxyjmmrw6vkbjmm4jx17i92rnc4mmcm3-transmission-3.00/lib
  | -
  | /gnu/store/pnq464qnrr5nrmhr3avn39b22axf1na8-transmission-3.00/bin
  | /gnu/store/pnq464qnrr5nrmhr3avn39b22axf1na8-transmission-3.00/share
  | /gnu/store/pnq464qnrr5nrmhr3avn39b22axf1na8-transmission-3.00/etc
  | /gnu/store/pnq464qnrr5nrmhr3avn39b22axf1na8-transmission-3.00/lib
  `----

  As I'm not very familiar with Guix build process and generations, I'm
  wondering what's the relevance of the files that are created in
  `/gnu/store' and whose file extensions are

  + `*.drv'
  + `*-builder'
  + `*.tar.xz.drv.'
  + `*.tar.xz-builder.'
  + `*-honor-localdir.patch'


3 The question
==============

  Is there any section in the Guix manual that explains the meaning of
  each extension and how they are important to the operating system or
  useful to the user? If not, could anyone briefly describe those file
  extensions please?