bug#52577: ‘guix lint’ throws an ugly backtrace if the GitHub updater receives “rate limit exceeded” error

[Xinglu Chen]

When running ‘guix lint -c refresh’ on a package hosted on GitHub, I get
an ugly backtrace when the GitHub rate limit has been reached.

--8<---------------cut here---------------start------------->8---
$ guix lint pipewire
fetching CVE database for 2021...
fetching CVE database for 2018...
Backtrace:ipewire@0.3.29 [refresh]...
          15 (primitive-load "/home/yoctocell/.config/guix/current/b…")
In guix/ui.scm:
   2206:7 14 (run-guix . _)
  2169:10 13 (run-guix-command _ . _)
In ice-9/boot-9.scm:
  1752:10 12 (with-exception-handler _ _ #:unwind? _ # _)
  1752:10 11 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
   658:37 10 (thunk)
In srfi/srfi-1.scm:
    634:9  9 (for-each #<procedure 7fb8f038ff40 at guix/scripts/lin…> …)
In guix/scripts/lint.scm:
     65:4  8 (run-checkers _ _ #:store _)
In srfi/srfi-1.scm:
    634:9  7 (for-each #<procedure 7fb8e15a8d20 at guix/scripts/lin…> …)
In guix/scripts/lint.scm:
    74:21  6 (_ _)
In guix/lint.scm:
   1428:5  5 (check-for-updates #<package pipewire@0.3.29 gnu/packag…>)
    771:2  4 (call-with-networking-fail-safe _ _ _)
In ice-9/boot-9.scm:
  1752:10  3 (with-exception-handler _ _ #:unwind? _ # _)
  1685:16  2 (raise-exception _ #:continuable? _)
  1683:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
ERROR:
  1. &http-get-error:
      uri: #<<uri> scheme: https userinfo: #f host: "api.github.com" port: #f 
path: "/repos/PipeWire/pipewire/releases" query: #f fragment: #f>
      code: 403
      reason: "rate limit exceeded"
  2. &message: "https://api.github.com/repos/PipeWire/pipewire/releases: HTTP 
download failed: 403 (\"rate limit exceeded\")"
--8<---------------cut here---------------end--------------->8---

When running ‘guix refresh’, a much friendlier error message is produced.

--8<---------------cut here---------------start------------->8---
$ guix refresh -t github
guix refresh: error: 
https://api.github.com/repos/OpenZWave/open-zwave/releases: HTTP download 
failed: 403 ("rate limit exceeded")
--8<---------------cut here---------------end--------------->8---

The problem seems to be that the ‘check-for-updates’ procedure in (guix
lint) doesn’t catch the ‘&http-get-error’.  I tried adding the following
form:

--8<---------------cut here---------------start------------->8---
(guard (c ((and (http-get-error? c)
                (string=? "rate limit exceeded"
                          (http-get-error-reason c)))
           (warning (G_ "GitHub rate limit exceeded"))
           #f))
  (with-networking-fail-safe ...))
--8<---------------cut here---------------end--------------->8---

but it doesn’t work.  C seems to be something a lot more complicated
than just a ‘&http-get-error’:

--8<---------------cut here---------------start------------->8---
#<&compound-exception components: (#<&error> #<&irritants irritants: 
(#<&compound-exception components: (#<&http-get-error uri: #<<uri> scheme: 
https userinfo: #f host: "api.github.com" port: #f path: 
"/repos/PipeWire/pipewire/releases" query: #f fragment: #f> code: 403 reason: 
"rate limit exceeded"> #<&message message: 
"https://api.github.com/repos/PipeWire/pipewire/releases: HTTP download failed: 
403 (\"rate limit exceeded\")">)>)> #<&exception-with-kind-and-args kind: 
%exception args: (#<&compound-exception components: (#<&http-get-error uri: 
#<<uri> scheme: https userinfo: #f host: "api.github.com" port: #f path: 
"/repos/PipeWire/pipewire/releases" query: #f fragment: #f> code: 403 reason: 
"rate limit exceeded"> #<&message message: 
"https://api.github.com/repos/PipeWire/pipewire/releases: HTTP download failed: 
403 (\"rate limit exceeded\")">)>)>)>
--8<---------------cut here---------------end--------------->8---

Any ideas on how to extract to the ‘&http-get-error’?

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