From e1dae4918bdc8c9a86d8d32746898d70f4eaf1da Mon Sep 17 00:00:00 2001
From: =?utf8?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
 (bug#67000)

* lisp/ielm.el (inferior-emacs-lisp-mode): Add support for saving input
history to a file.
(ielm--history-file-name): New variable indicating IELM input history
file.
(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.

* lisp/comint.el (comint-input-ring-file-name): Improve defcustom tag.

(cherry picked from commit 60cff1ac9d216e5abcb350ea5e623ab0b377c131)
---
 etc/NEWS       |  8 ++++++++
 lisp/comint.el |  2 +-
 lisp/ielm.el   | 29 +++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/etc/NEWS b/etc/NEWS
index 2c627512870..35a78d90f49 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1474,6 +1474,14 @@ 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/comint.el b/lisp/comint.el
index 0a9cdb44bef..655ff30469c 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -254,7 +254,7 @@ This variable is buffer-local."
 See also `comint-read-input-ring' and `comint-write-input-ring'.
 `comint-mode' makes this a buffer-local variable.  You probably want
 to set this in a mode hook, rather than customize the default value."
-  :type '(choice (const :tag "nil" nil)
+  :type '(choice (const :tag "Disable input history" nil)
 		 file)
   :group 'comint)
 
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 @@ This gives more frame width for large indented sexps, and allows functions
 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 @@ behavior of the indirect buffer."
     (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 @@ Customized bindings may be defined in `ielm-map', which currently contains:
             #'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
-- 
2.39.5