Subject: [bug#40077] [PATCH 0/4] Inferior provide stack traces along with exceptions

From: Ludovic Courtès <[email-masked]>
Date: Sun, 15 Mar 2020 18:00:19 +0100

Hello!

This patch series allows inferiors to provide stack traces when
an exception is thrown.

The wire format needed to be changed to provide that info, and thus
the protocol had to be adjusted to support both forward and backward
compatibility: a new client must be able to talk to an old ‘guix repl’,
and an old client must be able to talk to a new ‘guix repl’.  To that
end, clients now send the protocol version they support.

Note that, with these patches, stack traces are available but inferior
exceptions are not reported more nicely than before:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (open-inferior "/home/ludo/src/guix" #:command "scripts/guix")
$1 = #<<inferior> pid: pipe socket: #<input-output: file 7f08f4404a80> close: #<procedure close-pipe (p)> version: (0 1 1) packages: #<promise #<procedure 7f08f6813040 at guix/inferior.scm:161:32 ()>> table: #<promise #<procedure 7f08f43c6240 at guix/inferior.scm:162:32 ()>>>
scheme@(guile-user)> (inferior-eval '(throw 'x 'y 'z) $1)
ice-9/boot-9.scm:1669:16: In procedure raise-exception:
ERROR:
  1. &inferior-exception:
      arguments: (x y z)
      inferior: #<<inferior> pid: pipe socket: #<input-output: string 7f08f4404a80> close: #<procedure close-pipe (p)> version: (0 1 1) packages: #<promise #<procedure 7f08f6813040 at guix/inferior.scm:161:32 ()>> table: #<promise #<procedure 7f08f43c6240 at guix/inferior.scm:162:32 ()>>>
      stack: ((#f ("ice-9/boot-9.scm" 1763 13)) (raise-exception ("ice-9/boot-9.scm" 1668 16)) (#f (#f #f #f)) (#f ("guix/repl.scm" 92 21)) (with-exception-handler ("ice-9/boot-9.scm" 1735 10)) (with-exception-handler ("ice-9/boot-9.scm" 1730 15)) (#f ("guix/repl.scm" 119 7)))

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
--8<---------------cut here---------------end--------------->8---

This is left as an exercise to the reader.

Feedback welcome!

Ludo’.

Ludovic Courtès (4):
  repl: Allow clients to send their protocol version.
  inferior: Adjust to protocol (0 1).
  repl: Return stack traces along with exceptions.
  inferior: '&inferior-exception' includes a stack trace.

 guix/inferior.scm  | 24 +++++++++++--
 guix/repl.scm      | 86 ++++++++++++++++++++++++++++++++++++++--------
 tests/inferior.scm |  3 ++
 3 files changed, 97 insertions(+), 16 deletions(-)

-- 
2.25.1