From fe91c4f3aaefc109135c48ba26f8f21e87db465e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simen=20Heggest=C3=B8yl?= <simenheg@runbox.com>
Date: Tue, 16 Jan 2024 08:21:41 +0100
Subject: [PATCH] Add support for reading/writing IELM input history

* lisp/ielm.el (inferior-emacs-lisp-mode): Add support for
reading/writing input history.
(ielm--history-file-name): Name of the file to read/write IELM input
history.
(ielm--exit): Holds a function to call when Emacs is killed to write
out the input history.
(ielm--input-history-writer): Helper function for writing the IELM
input history out to file.
---
 etc/NEWS     |  8 ++++++++
 lisp/ielm.el | 29 +++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/etc/NEWS b/etc/NEWS
index ee7462cb2aa..2c98a805582 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1328,6 +1328,14 @@ characters, such as ½ (U+00BD VULGAR FRACTION ONE HALF), are also
 recognized as rational fractions.  They have been since 2004, but it
 looks like it was never mentioned in the NEWS, or even the manual.
 
+** IELM
+
+---
+*** IELM now remembers input history between sessions.
+The new user option 'ielm-history-file-name' is the name of the file
+where IELM input history will be saved.  Customize it to nil to revert
+to the old behavior of not remembering input history between sessions.
+
 
 * New Modes and Packages in Emacs 30.1
 
diff --git a/lisp/ielm.el b/lisp/ielm.el
index 777aebb70cf..e583e0fe32c 100644
--- a/lisp/ielm.el
+++ b/lisp/ielm.el
@@ -110,6 +110,13 @@ ielm-dynamic-multiline-inputs
 such as `edebug-defun' to work with such inputs."
   :type 'boolean)
 
+(defcustom ielm-history-file-name
+  (locate-user-emacs-file "ielm-history.eld")
+  "If non-nil, name of the file to read/write IELM input history."
+  :type '(choice (const :tag "Disable input history" nil)
+                 file)
+  :version "30.1")
+
 (defvaralias 'inferior-emacs-lisp-mode-hook 'ielm-mode-hook)
 (defcustom ielm-mode-hook nil
   "Hooks to be run when IELM (`inferior-emacs-lisp-mode') is started."
@@ -503,6 +510,17 @@ ielm--expand-ellipsis
     (funcall pp-default-function beg end)
     end))
 
+;;; Input history
+
+(defvar ielm--exit nil
+  "Function to call when Emacs is killed.")
+
+(defun ielm--input-history-writer (buf)
+  "Return a function writing IELM input history to BUF."
+  (lambda ()
+    (with-current-buffer buf
+      (comint-write-input-ring))))
+
 ;;; Major mode
 
 (define-derived-mode inferior-emacs-lisp-mode comint-mode "IELM"
@@ -605,6 +623,17 @@ inferior-emacs-lisp-mode
             #'ielm-indirect-setup-hook 'append t)
   (setq comint-indirect-setup-function #'emacs-lisp-mode)
 
+  ;; Input history
+  (setq-local comint-input-ring-file-name ielm-history-file-name)
+  (setq-local ielm--exit (ielm--input-history-writer (current-buffer)))
+  (setq-local kill-buffer-hook
+              (lambda ()
+                (funcall ielm--exit)
+                (remove-hook 'kill-emacs-hook ielm--exit)))
+  (unless noninteractive
+    (add-hook 'kill-emacs-hook ielm--exit))
+  (comint-read-input-ring t)
+
   ;; A dummy process to keep comint happy. It will never get any input
   (unless (comint-check-proc (current-buffer))
     ;; Was cat, but on non-Unix platforms that might not exist, so
-- 
2.39.2