From cabbb36ae1d089e34c501c54a682ea7121899565 Mon Sep 17 00:00:00 2001
From: Eli Zaretskii <eliz@gnu.org>
Date: Sat, 1 Mar 2025 10:27:17 +0200
Subject: [PATCH] Save IELM input history on "C-c C-c"

* lisp/ielm.el (ielm--write-history-on-interrupt): New function.
(inferior-emacs-lisp-mode): Install it as buffer-local value of
the 'interrupt-process-functions' hook.  (Bug#76585)

* etc/NEWS: Announce the behavior change.
---
 etc/NEWS     |  8 ++++++++
 lisp/ielm.el | 11 ++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/etc/NEWS b/etc/NEWS
index 0867822a7d8..2a973b77827 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -918,6 +918,14 @@ for docstrings where symbols 'nil' and 't' are in quotes.
 In most cases, having it enabled leads to a large amount of false
 positives.
 
+** IELM
+
+---
+*** IELM input history is now saved also when the IELM process is killed.
+When you kill the IELM process with "C-c C-c", the input history is now
+saved to the file specified by 'ielm-history-file-name', just like when
+you exit the Emacs session or kill the IELM buffer.
+
 ** DocView
 
 ---
diff --git a/lisp/ielm.el b/lisp/ielm.el
index b3cd02b4dc0..43529f36cd6 100644
--- a/lisp/ielm.el
+++ b/lisp/ielm.el
@@ -521,6 +521,12 @@ behavior of the indirect buffer."
     (with-current-buffer buf
       (comint-write-input-ring))))
 
+(defun ielm--write-history-on-interrupt (_proc _group)
+  "Save the IELM input history when the process is interrupted."
+  (funcall (ielm--input-history-writer (current-buffer)))
+  ;; Let the rest of the hook functions run as well.
+  nil)
+
 ;;; Major mode
 
 (define-derived-mode inferior-emacs-lisp-mode comint-mode "IELM"
@@ -658,7 +664,10 @@ Customized bindings may be defined in `ielm-map', which currently contains:
          '(rear-nonsticky t field output inhibit-line-move-field-capture t))))
     (comint-output-filter (ielm-process) ielm-prompt-internal)
     (set-marker comint-last-input-start (ielm-pm))
-    (set-process-filter (get-buffer-process (current-buffer)) 'comint-output-filter)))
+    (set-process-filter (get-buffer-process (current-buffer))
+                        'comint-output-filter)
+    (add-hook 'interrupt-process-functions
+              #'ielm--write-history-on-interrupt -1 t)))
 
 (defun ielm-get-old-input nil
   ;; Return the previous input surrounding point