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Re: [PATCH 1/1] gnu: eudev: Update home-page URL.
From: |
Leo Famulari |
Subject: |
Re: [PATCH 1/1] gnu: eudev: Update home-page URL. |
Date: |
Sun, 27 Dec 2015 19:43:42 -0500 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Sun, Dec 27, 2015 at 10:46:12AM -0500, Mark H Weaver wrote:
> Leo Famulari <address@hidden> writes:
>
> > On Fri, Dec 25, 2015 at 09:11:04AM -0500, Mark H Weaver wrote:
> >> Leo Famulari <address@hidden> writes:
> >> > * gnu/packages/linux.scm (eudev)[home-page]: Add up-to-date URL.
> >>
> >> Looks good, please push!
> >>
> >> This won't require any rebuilds, because the 'home-page' field is not
> >> included in the generated derivations.
> >
> > Ah, right, of course! Because it doesn't affect the sha256 hash of the
> > source.
>
> It's true that it doesn't affect the hash of the source, but that would
> not be sufficient to ensure no rebuilds. Adding a new phase would not
> change the hash of the source, but it would affect the _derivation_ (as
> serialized in the *.drv file) and thus would require rebuilds. The
> 'home-page' field is not included in the derivation.
>
> > And the same for the source URI?
>
> Changing the source URI affects the derivation that downloads the
> source, however, that derivation is of a special kind called a "fixed
> output derivation", which means that the sha256 hash of the output is
> known in advance. Such derivations do not need to be rebuilt even if
> the derivation changes, as long as the hash stays the same, because it
> is presumed that the output would not change.
Thank you for taking the time to explain this. For everyone reading
along, there is some more information about fixed-output derivations in
the manual here:
https://www.gnu.org/software/guix/manual/html_node/Derivations.html