Re: Turning off tests leads to a different store item

[Suhail <suhail@bayesians.ca>]

Simon Tournier <zimon.toutoune@gmail.com> writes:

> On Wed, 01 Nov 2023 at 17:52, Suhail <suhail@bayesians.ca> wrote:
>
>> If not, why should skipping the tests result in a different
>> derivation tree?
>
> The store path is different because it hashes all the inputs, included
> the builder script; from my understanding.

It certainly seems to be the case. Would you know the specific place(s)
in the source code (in addition to guix/derivations.scm and
guix/store.scm) that would be relevant for this discussion?

On a related note, is Dolstra's phd thesis relevant for these aspects,
or do you know if Guix diverges from Nix in some areas?

> Well, from my understanding, get the same the store path for the same
> package built with or without its tests ...  would mean to have a
> derivation for building and another derivation – referring to the
> former – for testing.

Yes, with the test derivation being something like a "fixed-output
derivation". [[info:guix#Derivations][From the manual]]:

#+begin_quote
Operations such as file downloads and version-control checkouts for
which the expected content hash is known in advance are modeled as
fixed-output derivations. Unlike regular derivations, the outputs of a
fixed-output derivation are independent of its inputs—e.g., a source
code download produces the same result regardless of the download method
and tools being used.
#+end_quote

The hypothetical test derivation leaves the build artifact unchanged,
but does communicate some "side" information. It's like a fixed-output
derivation carrying some metadata (further elaboration below).

> Well, taking this direction, one could imagine a derivation for each
> phases; somehow extend to all phases what it is already done for
> fetching source, build and grafts (guix build --source && guix build
> --no-grafts && guix build).

Perhaps not all. The thing that sets the "check" phase (#:tests?) apart
from the rest is that it's an identity transform with a
side-effect. i.e., it simply reports on the state of its input (i.e.,
the build artifact) leaving the build artifact unchanged. The only other
phase in the gnu-build-system that is similar to the "check phase" is
the "validate-runpath phase".

An alternative (possibly future) version of Guix might allow us to delay
the interpretation/meaning associated with the following cases:

- whether or not the tests were run, and
- whether or not the tests, if run, passed

To be able to do so, we need the "check derivation" be able to
communicate two things (downstream): a summary of the test phase (could
simply be a 3-valued datatype, like a 'Maybe Bool' in Haskell, but could
also be something more elaborate), and the input build artifact (which
remains unchanged). Similarly for the "validate-runpath derivation".

I do not know what the best way to communicate the "side-effect
information" (did the tests run and if so what was the conclusion) would
be. Specifically, should the output of "check derivation" (similarly for
"validate-runpath derivation") include the unchanged build artifact or
not?

Btw, is this still the appropriate mailing list (and more generally,
forum) for this discussion?

-- 
Suhail

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