bug#31236: [PATCH] Fix pre- and post-command-hook errors in term.el

[Karl Otness <karl@karlotness.com>]

[-- Attachment #1: Type: text/plain, Size: 1157 bytes --]

As far as I can tell there isn't an existing bug report for this
issue. It is very minor but I have attached a fix. This affects Emacs
26.1-rc1 `term' and `ansi-term'. In char mode term installs functions
in both pre- and post-command-hooks. After the process exits both of
these hooks produce errors and then are removed by Emacs after
printing a message.

Both of these hooks are re-installed when entering char mode and
removing them if they are not present will do nothing. To produce this
change, I took the remove-hook lines used when entering line mode and
placed them in `term-handle-exit'.

To reproduce the issue in 26.1, M-x term, exit the running process and
execute any command (i.e. move point). In *Messages* there should be
the following lines:

Error in pre-command-hook (term-set-goto-process-mark):
(wrong-type-argument processp nil)
Error in post-command-hook (term-goto-process-mark-maybe):
(wrong-type-argument processp nil)

The error seems to come up from `process-mark'. After this change,
these errors no longer appear as the hooks are removed. I have
attached a patch which applies this change to current master.

Thank you,
Karl

[-- Attachment #2: 0001-Fix-pre-and-post-command-hook-errors-in-term.el.patch --]
[-- Type: text/x-patch, Size: 987 bytes --]

From e988914505a694b00eaff60ca226400d998c19aa Mon Sep 17 00:00:00 2001
From: Karl Otness <karl@karlotness.com>
Date: Sat, 21 Apr 2018 23:01:11 -0400
Subject: [PATCH] Fix pre- and post-command-hook errors in term.el

Before this patch, after the terminal process dies the command hooks
added in term-mode's char mode would produce errors. This fix removes
these hooks when the process dies.
---
 lisp/term.el | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lisp/term.el b/lisp/term.el
index cfb39c34e5..017b0221ec 100644
--- a/lisp/term.el
+++ b/lisp/term.el
@@ -1456,6 +1456,9 @@ term-handle-exit
   (let ((buffer-read-only nil)
 	(omax (point-max))
 	(opoint (point)))
+    ;; Remove hooks to avoid errors due to dead process.
+    (remove-hook 'pre-command-hook #'term-set-goto-process-mark t)
+    (remove-hook 'post-command-hook #'term-goto-process-mark-maybe t)
     ;; Record where we put the message, so we can ignore it
     ;; later on.
     (goto-char omax)
-- 
2.17.0