bug#53355: guix shell --check: confusing error message

[Chris Marusich <cmmarusich@gmail.com>]

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Hi Ludo,

Thank you for the review!

Ludovic Courtès <ludo@gnu.org> writes:

> LGTM, please push!

Before pushing, I did some more tests to make sure it was still working.
When I did this, I noticed that read-line was no longer returning
strings that end in "\r".  This prevents child-shell-environment from
behaving correctly, since it incorrectly assumes that all the lines end
in "\r", stripping it off unconditionally.  In the past, I'm sure
read-line was returning strings that end in "\r".  I don't know what
changed, but I've attached a second patch that fixes this issue, also.

Unless you have more feedback, I'll go ahead and push both patches to
master in a few days.

-- 
Chris

PGP: https://savannah.gnu.org/people/viewgpg.php?user_id=106836

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From c4fee9e63f8cb694de86ae46bd1e2e4c692eb6f6 Mon Sep 17 00:00:00 2001
From: Chris Marusich <cmmarusich@gmail.com>
Date: Sun, 19 Jun 2022 13:16:04 -0700
Subject: [PATCH] environment: Don't assume that lines have a trailing "\r".

I've noticed that the child-shell-environment procedure is misbehaving on my
computer because the lines returned by read-line do not have a trailing "\r".
In the past, I recall that such lines did in fact have a trailing "\r".  I'm
not sure why it changed, but it seems prudent to just rewrite this code to
tolerate both cases, since it seems that both cases can happen.

* guix/scripts/environment.scm (child-shell-environment) [lines]: Instead of
checking if the line exactly matches "GUIX_CHECK_DONE\r"; check if the line
begins with "GUIX_CHECK_DONE".  Instead of always stripping the trailing
character from the line, only do it if the line has a trailing "\r".
---
 guix/scripts/environment.scm | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/guix/scripts/environment.scm b/guix/scripts/environment.scm
index f0cb341aab..1fb4f5b7c6 100644
--- a/guix/scripts/environment.scm
+++ b/guix/scripts/environment.scm
@@ -462,13 +462,18 @@ (define lines
                           ;; prompt from getting mixed into what we read.
                           (match (read-line shell-pipe-in)
                             ((? eof-object?) (reverse lines))
-                            ("GUIX-CHECK-DONE\r"
+                            ((? (lambda (line)
+                                  ;; The line might or might not have a trailing \r.
+                                  (string-prefix? "GUIX-CHECK-DONE" line)))
                              (display "done\n" port)
                              (reverse lines))
                             (line
-                             ;; Drop the '\r' from LINE.
-                             (loop (cons (string-drop-right line 1)
-                                         lines))))))))
+                             ;; Strip the trailing '\r' from LINE if present.
+                             (let ((stripped-line
+                                    (if (string-suffix? "\r" line)
+                                        (string-drop-right line 1)
+                                        line)))
+                               (loop (cons stripped-line lines)))))))))
          (close-port port)
          (close-port shell-pipe-in)
          (waitpid pid)
-- 
2.34.0


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