Re: [PATCH 1/1] gnu: eudev: Update home-page URL.

[Mark H Weaver]

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.

     Regards,
       Mark