Merge branch 'suspend-with-shell-for-jj-fzf'

* Branch commit log:
  README.md: describe contirb/suspend-with-shell.el
  contrib/suspend-with-shell.el: use (suspend-emacs) to run a custom command
	This works without use of `ioctl(TIOCSTI)` that (suspend-emacs) relies on

Signed-off-by: Tim Janik <timj@gnu.org>

Author: tim-janik

README.md

@@ -88,6 +88,16 @@ These scripts are aimed at developers and provide useful utilities for working w
 
 * **jj-undirty.el:** A simple Emacs lisp script that automatically runs `jj status` every time a buffer is saved to snapshot file modifications.
   `Usage: (load (expand-file-name "~/jj-fzf/contrib/jj-undirty.el"))`
+  This will install an after-save-hook that calls `jj-undirty` to snapshot the changes in a saved buffer in a jj repository.
+
+* **suspend-with-shell.el:** A simple Emacs lisp script that allows to suspend Emacs with a custom command.
+  ```
+  Usage:
+    ;; Suspend emacs with a custom command, without using `ioctl(TIOCSTI)`
+    (load (expand-file-name "~/jj-fzf/contrib/suspend-with-shell.el"))
+    ;; Suspend emacs and start jj-fzf on Ctrl+T
+    (global-set-key (kbd "C-t") (lambda () (interactive) (suspend-with-shell "jj-fzf")))
+  ```
 
 <!-- LICENSE -->
 ## License

contrib/suspend-with-shell.el

@@ -0,0 +1,25 @@
+;; This Source Code Form is licensed MPL-2.0: http://mozilla.org/MPL/2.0
+
+;; == suspend-with-shell ==
+;; Wrap `(suspend-emacs)` so that a subshell is executed with $SHELL pointing
+;; to a script that will run `COMMAND`. This way, emacs can be suspended
+;; to run another terminal process on the same tty, without using
+;; `ioctl(TIOCSTI)` - which `(suspend-emacs)` relies on but is not available
+;; in recent kernel versions.
+(defun suspend-with-shell (COMMAND)
+  "Call (suspend-emacs) with $SHELL assigned to a script that will run COMMAND"
+  (interactive)
+  (let ((oldshell (getenv "SHELL"))
+        (tfile (make-temp-file "emacssubshell"))
+        (script (concat "#!/usr/bin/env bash\nset -Eeu #-x\n" COMMAND "\n"))
+        (cannot-suspend 't)) ; force suspend-emacs to use sys_subshell
+    (with-temp-file tfile
+      (insert script))
+    (set-file-modes tfile #o700 'nofollow)
+    ;; see sys_subshell() in https://github.com/emacs-mirror/emacs/blob/master/src/keyboard.c
+    (setenv "SHELL" tfile)
+    (suspend-emacs)     ; this calls system($SHELL)
+    (setenv "SHELL" oldshell)
+    (delete-file tfile)
+    )
+  )