guix gc should keep around recent intermediate build ingredients by default

> [ This is a user/developer friendliness feature request. I’m not arguing

> that `guix gc` should do anything differently on a technical level, I’m

> just trying to argue that the default experience should be different. ]

>

> Current situation:

> I use a forked guix repository as my default channel, which

> includes a number of slow-to-build Haskell packages. Now and

> then, I run out of disk space. So I call `guix gc`, which invariably

> removes the store paths involved in building my current system generation,

> so the next call to `guix system reconfigure` takes hours.

>

> Desired situation:

> After calling `guix gc`, the paths that were involved in my last system

> build are still around, so reconfiguring doesn’t result in everything

> being rebuilt.

>

> (If there’s some way I can achieve that now, perhaps by explicitly managing

> some roots, or passing specific arguments to `guix gc`, I’d be happy to

> know! I’d still argue that we should try to make this the default behaviour,

> though.)

> Have you tried passing the options '--gc-keep-derivations=yes’ and

> '--gc-keep-outputs=yes' to guix-daemon?

>> Have you tried passing the options '--gc-keep-derivations=yes’ and

>> '--gc-keep-outputs=yes' to guix-daemon?

>

> I had not. I added that right now, and first tests seem to indicate

> that this helps. Thanks!

> Would it be a bad idea to make this the default?

> Alternatively, how about some kind of developer config fragment that

> would modify a system configuration with settings that are a good

> idea for Guix development, if not general use? That might also include

> things like setting the $%!^@!*^% guile backtrace columns variable

> for guix-daemon.