guix build--rounds=N does not behave as expected

[swedebugia]

Hi

Today I took a look at 
https://www.gnu.org/software/guix/packages/reproducibility.html

I then proceeded to try building some of the packages with issues.

I failed at first.

Why?
Because my goal was to build ONLY the offending package, not all of its 
build dependencies (specifying --no-substitutes results in the latter).

How?
$ guix build tor --rounds=2
substitute: updating substitutes from 'https://ci.guix.info'... 100.0%
substitute: updating substitutes from 'https://ci.guix.info'... 100.0%
3.5 MB will be downloaded:
   /gnu/store/7k793vhnv6mk6fhrg493gfby4lyy1107-tor-0.3.4.9
The following graft will be made:
   /gnu/store/z3y6kb1j0g5mkkbrzanf8jqs0bimiyfq-tor-0.3.4.9.drv
substituting /gnu/store/7k793vhnv6mk6fhrg493gfby4lyy1107-tor-0.3.4.9...
downloading from 
https://ci.guix.info/nar/gzip/7k793vhnv6mk6fhrg493gfby4lyy1107-tor-0.3.4.9...
 tor-0.3.4.9  3.4MiB               1.3MiB/s 00:03 [##################] 
100.0%

applying 1 graft for 
/gnu/store/z3y6kb1j0g5mkkbrzanf8jqs0bimiyfq-tor-0.3.4.9.drv...
grafting '/gnu/store/7k793vhnv6mk6fhrg493gfby4lyy1107-tor-0.3.4.9' -> 
'/gnu/store/2ri08yiksan4gk7nqjxj9vawq8gmp6ip-tor-0.3.4.9'...
applying 1 graft for 
/gnu/store/z3y6kb1j0g5mkkbrzanf8jqs0bimiyfq-tor-0.3.4.9.drv...
grafting '/gnu/store/7k793vhnv6mk6fhrg493gfby4lyy1107-tor-0.3.4.9' -> 
'/gnu/store/2ri08yiksan4gk7nqjxj9vawq8gmp6ip-tor-0.3.4.9'...
successfully built 
/gnu/store/z3y6kb1j0g5mkkbrzanf8jqs0bimiyfq-tor-0.3.4.9.drv
/gnu/store/2ri08yiksan4gk7nqjxj9vawq8gmp6ip-tor-0.3.4.9
address@hidden:~$ guix build tor --rounds=2 --no-grafts
/gnu/store/7k793vhnv6mk6fhrg493gfby4lyy1107-tor-0.3.4.9

I tried also to specify --no-substitutes AFTER having run guix 
environment tor to make sure I had the substitutes of the build 
dependencies, but I failed anyway.

Did I misunderstand something?

Now it worked! I specified --check and --no-grafts and it began to do as 
I said.

I really think we should signal a helpful error to the user if only 
--rounds=N is specified and --check is missing.

--
Cheers Swedebugia