From 8749f31485888c587c6f88a0a7bdd48cc9e8c9b8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Fri, 5 May 2023 18:22:56 +0200
Subject: [PATCH] read-print: Correctly read "(. x)".

* guix/read-print.scm (read-with-comments): Check whether REST is a pair
before calling 'set-cdr!'.
* tests/read-print.scm ("read-with-comments: half dot notation"): New test.
---
 guix/read-print.scm  | 8 +++++---
 tests/read-print.scm | 5 +++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/guix/read-print.scm b/guix/read-print.scm
index d834105dce..83b9a61b35 100644
--- a/guix/read-print.scm
+++ b/guix/read-print.scm
@@ -179,9 +179,11 @@ (define (reverse/dot lst)
       (match lst
         (() result)
         (((? dot?) . rest)
-         (let ((dotted (reverse rest)))
-           (set-cdr! (last-pair dotted) (car result))
-           dotted))
+         (if (pair? rest)
+             (let ((dotted (reverse rest)))
+               (set-cdr! (last-pair dotted) (car result))
+               dotted)
+             (car result)))
         ((x . rest) (loop (cons x result) rest)))))
 
   (let loop ((blank-line? blank-line?)
diff --git a/tests/read-print.scm b/tests/read-print.scm
index c2b236b172..9e1d8038f1 100644
--- a/tests/read-print.scm
+++ b/tests/read-print.scm
@@ -58,6 +58,11 @@ (define-syntax-rule (test-pretty-print/sequence str args ...)
   (call-with-input-string "(a . b)"
     read-with-comments))
 
+(test-equal "read-with-comments: half dot notation"
+  '(lambda x x)
+  (call-with-input-string "(lambda (. x) x)"
+    read-with-comments))
+
 (test-equal "read-with-comments: list with blank line"
   `(list with ,(vertical-space 1) blank line)
   (call-with-input-string "\