Hi Guix,

See: <https://lists.gnu.org/archive/html/guix-devel/2021-03/msg00538.html>

* Patch #1: Use 'gtk-doc/stable' instead of 'gtk-doc' in native-inputs

To test packages can still be built:

<start snip>
PACKAGES="thermald glimpse glib mate-desktop atril caja-extensions"
PACKAGES+=" mate-utils eom engrampa pluma mate-polkit"
PACKAGES+=" libgnt loudmouth denemo gsequencer libu2f-host libu2f-server"
PACKAGES+=" keybinder keybinder-3.0"

./pre-inst-env guix build $PACKAGES -M

# Output:
The following derivation will be built:
   /gnu/store/n84fwcigw3djfxv12iqv76bwp2gx9mnf-denemo-2.5.0.drv
The following files will be downloaded:
[...]

./pre-inst-env guix build denemo
[Bla bla.]
# Success!

<end snip>

To test no references to imagemagick or gtk-doc are retained:

./pre-inst-env guix graph --type=references $PACKAGES
# ^ search for imagemagick in output
# ^ TODO it should not be required to substitute $PACKAGES
#   first, as the 'references' information is in the narinfo.

* Patch #2: Export canonicalize-reference
* Patch #3: Add a '#:disallowed-references' argument to 'python-build'.

Used in later patches.

* Patch #4: Let 'python-sphinx' use 'imagemagick/stable'.

python-sphinx depends on imagemagick.  As (before this patch series),
many packages depend on 'python-sphinx' ...

<start snip>
guix refresh --list-dependent python-sphinx
Building the following 199 packages would ensure 427 dependent packages are rebuilt: [...]
<end snip>

... it may be worthwile to depend a /stable variant of python-sphinx,
and use it when sphinx is used only for generating the documentation.
However, defining a variant of python-sphinx is not required,
as python-sphinx does not retain its reference to imagemagick.

Thus, I simply replaced 'imagemagick' with 'imagemagick/stable' in the
inputs.  To make sure python-sphinx does not retain references to imagemagick/stable,
I added #:disallowed-references `(,imagemagick/stable) to #:arguments.

It is commented out in the patch to avoid rebuilds:

$ ./pre-inst-env guix build python-sphinx
> substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
> 1.6 MB will be downloaded:
>    /gnu/store/sf2kdppaf8z2ri40rlp27l7ffkd8kvyf-python-sphinx-3.3.1
> substituting /gnu/store/sf2kdppaf8z2ri40rlp27l7ffkd8kvyf-python-sphinx-3.3.1...
> downloading from https://ci.guix.gnu.org/nar/lzip/sf2kdppaf8z2ri40rlp27l7ffkd8kvyf-python-sphinx-3.3.1 ...
>  python-sphinx-3.3.1  1.5MiB                                    121KiB/s 00:13 [##################] 100.0%
> [...]

When uncommented, 'python-sphinx' still builds.


* Patch #5 .. #10: I replaced imagemagick with imagemagick/stable in some packages

* After this patch series: how many packages would be rebuild if imagemagick
  is updated?

$ ./pre-inst-env guix refresh --list-dependent imagemagick@6.9.12-4
> Building the following 47 packages would ensure 73 dependent packages are rebuilt: [..]

Also, I verified ./pre-inst-env guix build guix still succeeds.

Greetings,
Maxime.