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

[Xinglu Chen]

On So, Dez 19 2021, Maxime Devos wrote:

> Xinglu Chen schreef op vr 17-12-2021 om 21:57 [+0100]:
>> On Fri, Dec 17 2021, Maxime Devos wrote:
>> 
>> > Xinglu Chen schreef op vr 17-12-2021 om 15:03 [+0100]:
>> > > (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 ...))
>> > 
>> > Shouldn't this be wrapped the other way around?
>> > Or maybe even move the http-get-error?+string=?+warning inside
>> > call-with-networking-fail-safe?
>> 
>> Thanks for the pointer, it seems that ‘throw’ in
>> ‘call-with-networking-fail-safe’ wraps the original exception an
>> additional ‘&compound-exception’.  Before the ‘throw’, the exception
>> looks like this:
>> 
>> --8<---------------cut here---------------start------------->8---
>> (%exception #<&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---
>> 
>> After the ‘throw’, it becomes this:
>> 
>> --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---
>> 
>> This means that the ‘guard’ form in ‘call-with-networking-fail-safe’
>> is
>> never going to match anything since the real exception will always be
>> nested
>> in another ‘&compound-exception’.
>
> Actually, being wrapped in &compound-exception shouldn't be a problem:
> &compound-exception just means that the exception is of multiple types,
> e.g. both &message and &http-get-error or something like that. In that
> case, the exception could be both message? and http-get-error?.
>
> I think the problem is, that for some unknown reason, the
> &http-get-error/&message exception gets wrapped in a
> &exception-with-and-args --- I guess there's a bad interaction with
> the throw/catch exception handling system and the raise/guard system,
> because only 'system-error'/'tls-certificate-error'/...-style
> exceptions should get wrapped in a &exception-with-kind-and-arguments.

Yeah, the catch/throw system doesn’t really work well with ‘raise’.
Here is what I found after some digging:

(catch KIND THUNK HANDLER) uses ‘exception-kind’ to determine the kind
of the exception.  Since ‘&http-get-error’ was created using ‘raise’, it
doesn’t really have a notion of a “kind”, therefore, ‘exception-kind’
returns the ‘%exception’ symbol.  I guess that’s why I had to match on
('%exception exception) to match the ‘&http-get-error’

Excerpt from the patch I attached:

  (catch #t
    proc
    (match-lambda*
      ...
      ((and ('%exception exception)
            (http-get-error? exception))
        ...)
        ...))

0001-lint-Fix-handling-of-HTTP-errors.patch
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