read-print: 'pretty-print-with-comments' keeps newlines on long strings.

* guix/read-print.scm (printed-string)[preserve-newlines?]: New
procedure.
Use it to preserve newlines on long strings.
* tests/read-print.scm: Add test.

2 files changed, 14 insertions, 2 deletions

diff --git a/guix/read-print.scm b/guix/read-print.scm
index 515eb7669c7..d834105dce7 100644
--- a/guix/read-print.scm
+++ b/guix/read-print.scm
@@ -420,11 +420,18 @@ particular newlines, is left as is."
 
 (define (printed-string str context)
   "Return the read syntax for STR depending on CONTEXT."
+  (define (preserve-newlines? str)
+    (and (> (string-length str) 40)
+         (string-index str #\newline)))
+
   (match context
     (()
-     (object->string str))
+     (if (preserve-newlines? str)
+         (escaped-string str)
+         (object->string str)))
     ((head . _)
-     (if (memq head %natural-whitespace-string-forms)
+     (if (or (memq head %natural-whitespace-string-forms)
+             (preserve-newlines? str))
          (escaped-string str)
          (object->string str)))))
 
diff --git a/tests/read-print.scm b/tests/read-print.scm
index f4627e076a4..c2b236b1721 100644
--- a/tests/read-print.scm
+++ b/tests/read-print.scm
@@ -195,6 +195,11 @@ expressions."
 (string-append \"a\\tb\" \"\\n\")")
 
 (test-pretty-print "\
+(display \"This is a very long string.
+It contains line breaks, which are preserved,
+because it's a long string.\")")
+
+(test-pretty-print "\
 (description \"abcdefghijkl
 mnopqrstuvwxyz.\")"
                    #:max-width 30)