Hi,

When two users run "guix pull" using the same commit, two different
versions of "guix-latest" get built.  This surprised me, and in any case
it seems inefficient to build the same version of Guix two times.  Why
do two different derivations get built?

Here's an invocation of "guix pull" as an unprivileged user:

--8<---------------cut here---------------start------------->8---
$ guix pull
...
Building from Git commit ed0f9f53abef57b9f33d3b2eada40375894bdff6...
...
The following derivation will be built:
   /gnu/store/m3x8069x5aspc29m9ay7idndz0kpfxlb-guix-latest.drv
copying and compiling to '/gnu/store/dn13gs9w16h5w6l77pnpbclqxnbyhh4m-guix-latest' with Guile 2.2.2...
--8<---------------cut here---------------end--------------->8---

And here's an invocation of "guix pull" as root:

--8<---------------cut here---------------start------------->8---
# guix pull
...
Building from Git commit ed0f9f53abef57b9f33d3b2eada40375894bdff6...
...
The following derivation will be built:
   /gnu/store/675pz9f4qz9dd4jikzcgzv62kjrxfhmg-guix-latest.drv
copying and compiling to '/gnu/store/cvc0rf65s3mjw9rjps80ram3898qdws3-guix-latest' with Guile 2.2.2...
--8<---------------cut here---------------end--------------->8---

I am surprised that these two invocations of "guix pull" build different
derivations.  I understand that the overall "guix pull" action requires
side effects outside of the store which will be different depending on
who invoked the command (e.g., to update the $HOME/.config/guix/latest
symlink), but that stuff isn't performed by a derivation.  I expect two
derivations that build Guix (or any software component) from the same
source to be identical, so I am surprised.

I have looked at the source code for "guix pull," and I cannot find any
obvious reason why the derivations should differ.  Does anyone know why
they differ?

-- 
Chris