bug#58567: Some grafts use a different input derivation than computed by --no-grafts

[Marius Bakke]

Hello,

Sorry for the indescriptive title, I'm not entirely sure what is going
wrong here.  The problem is that for some packages, 'guix build -d foo'
has a different input derivation than the one produced by
'guix build --no-grafts -d foo'.

As an example, as of commit 3d8c243efb615c7e642942433be1c7badf0ae65e,
'guix build -d telegram-desktop' produces:

  /gnu/store/q1gx5xaszlyyr0sx663c2qkx92cqbr4r-telegram-desktop-4.2.2.drv

If we open that graft derivation, we see that it depends on:

  /gnu/store/92bl6qmj5r0byc59fykvlfaqmw6ikvy8-telegram-desktop-4.2.2.drv

However:

  $ guix build -d --no-grafts telegram-desktop
  /gnu/store/4vbj4gblmwvl645z1q3aaxfhckjqi3kg-telegram-desktop-4.2.2.drv

As a result:

  $ guix build telegram-desktop
  /gnu/store/6k2rdbc2v6nqyj2g445dii8gkamnbs43-telegram-desktop-4.2.2
  $ guix build --no-grafts telegram-desktop
  The following derivations will be built:
    /gnu/store/4vbj4gblmwvl645z1q3aaxfhckjqi3kg-telegram-desktop-4.2.2.drv
    /gnu/store/n0rdkaf91ifyvsr81hxcdlb8hg8k6rgh-fcitx-qt5-1.2.6.drv

This was discovered because users reported[0] missing substitutes for
telegram-desktop despite it being built by Cuirass.  We can see that it
has built the --no-grafts derivation:

  https://ci.guix.gnu.org/build/1626416/details

...which is not being requested by end-users.

I have a hunch that this has to do with the grafting code affecting
origins (with gexps?), but have not confirmed this.

"Trivial" grafted packages such as 'perl-xml-parser' do not exhibit this
problem.

[0] https://logs.guix.gnu.org/guix/2022-10-16.log#152428

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