Re: Guix pull: avoiding "Computing Guix derivation"

[Simon Tournier]

Hi,

On lun., 13 mai 2024 at 17:11, Richard Sent <richard@freakingpenguin.com> wrote:

> Instead of A and B building C directly, A and B download the
> substitutable Guix package D, then use D to build C. Because D is a
> reproducible package, it should be substitutable from both A and B.
> Then, because D->C is the same for everyone, we could substitute the
> Guix derivation computation for C.

Maybe I am missing some details.  From my understanding, your D is the
result of the “Computing derivation” dance.  And it is a minimalist
build because it must work for both cases: with or without substitutes.

Somehow, my understanding of the current process is:

  A -> D  -> C
  B -> D* -> C

And, D or D* can be the same script.  Here, the property is a kind of
idempotency.  Hence, C is substitutable.

IIUC, your proposal is to fix D (the intermediary step).  You propose
the package named ’guix’ that changes barely, but it could be something
more minimalist.  The requirements is: susbtitutable.  The problem is
transferred to the first arrow, no?

How can we be sure that A and B points to the same D?

Other said, A lives in the past.  Later, we changed D becoming D*
because some bugs.  The other revision B lives after this change.
Therefore, we have the same picture:

  A -> D
  B -> D*

But then how do we go to C since D and D* does not have a kind of
idempotent property.

>From my understanding, the current situation/process is very similar
with the one for compiling compiler: you have your new Source of
compiler and an OldCompiler binary, so you run:

  OldCompiler(Source) -> Compiler
  and again Compiler(Source) -> NewCompiler

Somehow, whatever the choice of some OldCompiler binary, you get the
same NewCompiler binary (aside trusting trust attack and friends,
obviously ;-))

The story of “guix pull” is not so different; from my understanding.

Again, maybe I am missing something.


Cheers,
simon