Hello!

Ricardo Wurmus <rekado@elephly.net> skribis:

> Ludovic Courtès <ludovic.courtes@inria.fr> writes:
>
>> Ricardo Wurmus <rekado@elephly.net> skribis:

[...]

>>> Currently, there’s no way to tell if the derivations listed under “These
>>> derivations will be built” are expensive package builds or just simple
>>> graft derivations.
>>
>> Indeed.  A simple trick would be to (ab)use the environment variable
>> part of derivations as a property list, the way Nix has traditionally
>> done it (see ‘user+system-env-vars’ in (guix derivations)).
>>
>> So we could have, say, a ‘hint’ environment variable, and the UI would
>> use that to determine if it’s a graft.
>
> This sounds like a good trick to me.  I think it would be great to give
> more hints to the UI and make it clearer to users what work they can
> expect Guix to perform.

In a similar vein, the attached module provides code to estimate package
build time based on locally-available build logs.  It can be used to
show hints like this:

--8<---------------cut here---------------start------------->8---
The following derivations would be built (estimated time: 54 mn):
   /gnu/store/3627svyhih9cfss8gnxllp9nmxqp23cq-gcc-4.9.4.drv
   /gnu/store/3didvp9c3sfqwmb9kkdr211vg5myygsf-gcc-4.9.4.tar.xz.drv
--8<---------------cut here---------------end--------------->8---

or:

--8<---------------cut here---------------start------------->8---
The following derivations would be built (estimated time: 22 hr):
   /gnu/store/safjgjqhxlf59rknygqdfq175cl5wvks-rust-1.27.2.drv
   /gnu/store/v154ah7f8wqcga104df9ldb25bjk2pm8-rustc-1.27.2-src.tar.gz.drv
   /gnu/store/nz2xzl1yizcwcxhnw2w5mdqnp3q1gggx-rustc-1.25.0-src.tar.gz.drv
   /gnu/store/wn422brymn6ysxq07090ijb4wx78dc1l-rustc-1.24.1-src.tar.gz.drv
   /gnu/store/3cj5083j5aq7az7n5dmkds77g84xqc33-rust-bootstrap-1.22.1.drv
   /gnu/store/rm1nghqrvw43wlbwws49rw921qh58m35-rustc-1.23.0-src.tar.xz.drv
   /gnu/store/a9gzrq0bsc3ynfj4cnrsxxd2jwjgf4zj-rust-1.23.0.drv
   /gnu/store/bmbpbhgby84yrj0mvkv279cy2ira4xqf-rustc-1.24.1-src.tar.xz.drv
   /gnu/store/bxxyzp6kzq88ii4aindgnggbb2m193rk-rust-1.24.1.drv
   /gnu/store/r26s0y5fi055pclhnivvf63llbrj54yw-rustc-1.25.0-src.tar.xz.drv
   /gnu/store/x4l0rsqni9lglfzazkjyxqjp432yr33s-rustc-1.26.2-src.tar.gz.drv
   /gnu/store/03y9zf5imbm0ni1llcmxixb8c78nmxdd-rustc-1.26.2-src.tar.xz.drv
   /gnu/store/ici0m0bia0f6f4wh0ykn12x6wg1ckck0-rust-1.25.0.drv
   /gnu/store/2l6fn1nxs2sfl93khki5jzz6dh7gfqpr-rust-1.26.2.drv
   /gnu/store/9bn1gxnsc59zi8bdpvfgqcjpczmk3ch0-rustc-1.27.2-src.tar.xz.drv
--8<---------------cut here---------------end--------------->8---

(That’s from my x86_64 laptop.)

The obvious downside is that it works by first retrieving the names of
the files under /var/log/guix/drvs, and then opening, decompressing, and
parsing the candidate log files.  That typically takes a few seconds on
a recent SSD laptop, but clearly we don’t want to do that every time.
We could maintain a cache, but even then, it might still be too
expensive.

Perhaps we should keep build times in the database somehow; the daemon
can keep it up-to-date.

Thoughts?

There’s the obvious downside that both approaches rely on having
previously built the package, but I think that’s a necessary limitation,
unless we are to resort to external services (which could hardly provide
estimates that make sense for the user’s machine anyway.)

Ludo’.