Subject: [bug#55242] [PATCH 07/10] guix: import: go: More resilience wrt network errors; add logging.

From: Attila Lendvai <[email-masked]>
Date: Tue, 03 May 2022 17:00:30 +0000

> > +                   (let ((port (current-warning-port)))
> > +                     (format port "Unexpected error, will skip ~S.~%reason: "
> > +                             package-name)
> > +                     ;; Printing a backtrace here is not very useful: it is
> > +                     ;; cut off because GUARD unwinds.
> > +                     (print-exception port (stack-ref (make-stack #t) 1)
> > +                                      c (exception-args c))
> > +                     (display-backtrace (make-stack #t) port))
>
>
> Why are unknown errors being catched here?

*all* errors are caught, displayed, and swallowed, so that the importing can proceed to the rest of the packages.

a possible scenario: a large import can take several minutes. if there's a transient network error, then this way it may finish with 99% of the packages, and the rest can be restarted by hand after inspecting the log output.

another scenario is that the importer is simply buggy, and the user gets 99% of the packages imported, and has to do only one package by hand.

> What's the '-continuable' for here?  Is it to avoid extra 'raise-
> exception' entries in the backtrace, or does this actually make use
> of Scheme's continuable exceptions?

honestly, i can't remember. which translates to: i should have
commented on that!

*shakes head and makes a mental note*

from guile's manual:

"If continuable? is true, the handler is invoked in tail position
relative to the raise-exception call. Otherwise if the handler
returns, a non-continuable exception of type &non-continuable is
raised in the same dynamic environment as the handler."

i.e. it should rather be called raise-continuably not
raise-continuable.

and i think the reason is that the stack is not unwound that way, so
that the handlers in the guard can print a backtrace showing the
entire stack.

does this make sense? i'm still learning scheme's stack/exception
handling...

or maybe what i wanted is that the handlers in the guard can return
with (values #f '())? but i think that should work with vanilla RAISE,
too.

> Why a warning instead of a 'report-error'?

because i want the importer to be able to deal with a transitive
closures of dependencies with > 400 entries. if it fails at the first
error, then a `guix import go -r` becomes a hopeless endeavor for
larger go modules.

thanks for the review Maxime! i'll address the rest, too.

--
• attila lendvai
• PGP: 963F 5D5F 45C7 DFCD 0A39
--
“'Emergencies' have always been the pretext on which the safeguards of individual liberty have been eroded.”
	— F. A. Hayek (1899–1992)