rmail-summary-by-senders defaults to sender

* etc/NEWS: Mention this.
* lisp/mail/rmailsum.el (rmail-summary-by-senders):
Offer From field of current message as a default argument.

2 files changed, 15 insertions, 2 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 87c3950b1e3..5568e29eb8e 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -522,6 +522,10 @@ been removed.  Use 'encode-coding-string', 'decode-coding-string', and
 If this option is non-nil, messages appended to an output file by the
 'rmail-output' command have their Deleted flag reset.
 
+*** The command 'rmail-summary-by-senders' with an empty argument
+selects the messages to summarize with a regexp that matches the
+sender of the current message.
+
 * New Modes and Packages in Emacs 27.1
 
 +++
diff --git a/lisp/mail/rmailsum.el b/lisp/mail/rmailsum.el
index 3dd486a792a..e5363d2198c 100644
--- a/lisp/mail/rmailsum.el
+++ b/lisp/mail/rmailsum.el
@@ -390,8 +390,17 @@ SUBJECT is a regular expression."
 ;;;###autoload
 (defun rmail-summary-by-senders (senders)
   "Display a summary of all messages whose \"From\" field matches SENDERS.
-SENDERS is a regular expression."
-  (interactive "sSenders to summarize by: ")
+SENDERS is a regular expression.  The default for SENDERS matches the
+sender of the current messsage."
+  (interactive
+   (let* ((def (rmail-get-header "From"))
+          ;; We quote the default argument, because if it contains regexp
+          ;; special characters (eg "?"), it can fail to match itself.
+          (sender (regexp-quote def))
+          (prompt (concat "Senders to summarize by (regexp"
+                          (if sender ", default this message's sender" "")
+                          "): ")))
+     (list (read-string prompt nil nil sender))))
   (rmail-new-summary
    (concat "senders " senders)
    (list 'rmail-summary-by-senders senders) 'rmail-message-senders-p senders))