Re: 'guix build' and garbage collection

[Ludovic Courtès]

Hi Chris,

Chris Marusich <address@hidden> skribis:

> My understanding is that Nix builds derivations in a temporary
> directory.  My understanding is that eventually, we copy the results of
> the build into the final, content-addressed store path.  Since we don't
> know the final, content-addressed store path until after we calculate
> the hash of the output, how do we prevent that final store path from
> being garbage collected while the build process is running?  Do we use
> addTempRoot to add the final, content-addressed store path as a
> temporary root, too?  I looked in the code but couldn't figure this out.

Store items are not content-addressed, except for fixed-output
derivations and things added with ‘add-to-store’ and
‘add-text-to-store’.

Leaving these two special cases aside, store file names are computed as
a function of the build inputs of a derivation.  In Eelco Dolstra’s
thesis, both models are described: the “extensional model” (the one Nix
and Guix use) and the “intensional model” (content-addressability, which
has never been deployed, and which is challenging in many ways.)

HTH!

Ludo’.