Fix updating members of zip archives

* lisp/arc-mode.el (archive-zip-case-fiddle): Change the
default to nil except on MS-DOS.  Update the doc string to
make clear that a non-nil value also affects updating the
archive.  (Bug#38260)

1 files changed, 8 insertions, 3 deletions

diff --git a/lisp/arc-mode.el b/lisp/arc-mode.el
index 7f435f17a17..0cdc8a147d2 100644
--- a/lisp/arc-mode.el
+++ b/lisp/arc-mode.el
@@ -291,11 +291,16 @@ Archive and member name will be added."
                        (string :format "%v")))
   :group 'archive-zip)
 
-(defcustom archive-zip-case-fiddle t
-  "If non-nil then zip file members may be down-cased.
+(declare-function msdos-long-file-names "msdos.c")
+(defcustom archive-zip-case-fiddle (and (eq system-type 'ms-dos)
+                                        (not (msdos-long-file-names)))
+  "If non-nil, then all-caps names of zip file members will be down-cased.
 This case fiddling will only happen for members created by a system
-that uses caseless file names."
+that uses caseless file names.
+In addition, this flag forces members added/updated in the zip archive
+to be truncated to DOS 8+3 file-name restrictions."
   :type 'boolean
+  :version "27.1"
   :group 'archive-zip)
 ;; ------------------------------
 ;; Zoo archive configuration