bug#28659: Always enable substitutes for fixed-output derivations

[Ludovic Courtès]

address@hidden (Ludovic Courtès) skribis:

> So I think we have to communicate more info from the daemon to ‘guix
> substitute’.

The attached patch addresses that by simply calling out to the daemon to
determine whether we’re dealing with a content-addressed item.

To summarize, the new behavior is that substitutes are always enabled
for fixed-output derivations.  That way, people willing to build
everything from source can still use ‘--no-substitutes’ and yet be able
to retrieve source code without being penalized compared to someone
enabling substitutes wholesale.

Of course, when substitutes are missing, we fall back to regular
downloads or VCS checkouts.  It is also still possible to choose where
substitutes are downloaded from, using ‘--substitute-urls’, or even to
pass an empty list of URLs.

Feedback welcome!

Ludo’.

0001-substitute-Always-allow-substitutes-for-fixed-output.patch
Description: Text Data

0002-Revert-download-Download-a-nar-when-a-VCS-checkout-f.patch
Description: Text Data