help with copy-build-system

[Cameron]

Hello,

I am new to Guix but it seems to be the perfect tools for running a small 
cluster of servers that I need to administer. The one thing that so far is 
holding me back from doing so is the absence of a package for Caddy 
(https://caddyserver.com) which this cluster relies on heavily. I hope in the 
future to package it properly, but it has a number of golang dependencies that 
are not themselves even packaged, and I am far from an expert on building Go 
software -- it seems doable but it would be a relatively big undertaking.

Instead, I thought I could create a private package with copy-build-system and 
simply install the pre-built binaries that the Caddy project provides. This is 
the caddy-package.scm that I have come up with:
> 
> (use-modules (guix)
>              (guix build-system copy)
>      (guix build utils)
>              (guix licenses))
> 
> 
> (package
> (name "caddy")
> 
> (version "2.2.1")
> 
> (source
>   (origin
>    (method url-fetch)
>    (uri (string-append 
> "https://github.com/caddyserver/caddy/releases/download/"; version "/caddy_" 
> version "_linux_amd64.tar.gz"))
>    (sha256
>     (base32
>      "1va2h8hpxcby9rny7px1y2xks79rxb4svnf9mrdrlc5xn0s04dsx"))))
> 
> (build-system copy-build-system)
> 
> (arguments
>   '(#:install-plan '(("caddy" "bin/caddy"))))
> 
> (synopsis "This is a *BAD* Caddy package. It just pulls the already-built 
> binary from Github, rather than building from source.")
> (description "See https://caddyserver.com/";)
> (home-page "https://caddyserver.com/";)
> (license asl2.0))

When I build this file with `guix build -f caddy-package.scm -K', it fails with 
this rather mysterious (to me) error during the unpack phase:

> starting phase `unpack'
> LICENSE
> README.md
> caddy
> Backtrace:
>            8 (primitive-load "/gnu/store/fa16h805lxm1fmyhdmnwd09cpd7…")
> In ice-9/eval.scm:
>    191:35  7 (_ #f)
> In guix/build/gnu-build-system.scm:
>     838:2  6 (gnu-build #:source _ #:outputs _ #:inputs _ #:phases . #)
> In ice-9/boot-9.scm:
>   1736:10  5 (with-exception-handler _ _ #:unwind? _ # _)
> In srfi/srfi-1.scm:
>    857:16  4 (every1 #<procedure 7ffff634c0a0 at guix/build/gnu-bui…> …)
> In guix/build/gnu-build-system.scm:
>    847:30  3 (_ _)
>    164:15  2 (unpack #:source _)
>      65:2  1 (first-subdirectory _)
> In ice-9/boot-9.scm:
>   1669:16  0 (raise-exception _ #:continuable? _)
> 
> ice-9/boot-9.scm:1669:16: In procedure raise-exception:
> Throw to key `match-error' with args `("match" "no matching pattern" ())'.
> note: keeping build directory `/tmp/guix-build-caddy-2.2.1.drv-20'
> builder for `/gnu/store/p65q2ndw8hcpiq2x62jb9mxv6xa88kkn-caddy-2.2.1.drv' 
> failed with exit code 1
> build of /gnu/store/p65q2ndw8hcpiq2x62jb9mxv6xa88kkn-caddy-2.2.1.drv failed
> View build log at 
> '/var/log/guix/drvs/p6/5q2ndw8hcpiq2x62jb9mxv6xa88kkn-caddy-2.2.1.drv.bz2'.
> guix build: error: build of 
> `/gnu/store/p65q2ndw8hcpiq2x62jb9mxv6xa88kkn-caddy-2.2.1.drv' failed

Would anyone be able to give me any advice here? This seems to comport with the 
Reference Manual blurb 
(https://guix.gnu.org/manual/en/guix.html#index-copy_002dbuild_002dsystem) 
about copy-build-system and also appears similar to several official packages 
using copy-build-system (e.g. gcide, vim-neocomplete, neverball) that I looked 
to as examples. Clearly though, there is some nuance that I am missing.

Thanks in advance for any help you can provide.

-Cam Tindall