Subject: Re: bug#19812: 24.4; suggest `shell-mode' not interactive

From: Lars Ingebrigtsen <[email-masked]>
Date: Fri, 02 Aug 2019 21:52:17 +0200

Kevin Ryde <[email-masked]> writes:

> The `shell-mode' function is interactive, but I think perhaps it should
> not be since it is not designed for use as M-x shell-mode in an
> arbitrary buffer, but only after the `shell' function makes various
> setups.
>
> I struck this when a brain fade confused me between shell-command,
> shell-mode and shell and I did M-x shell-mode in a file buffer and
> nearly made a big mess.  The problem is only seen when shell.el has been
> loaded (for any reason) since shell-mode is not autoloaded.
>
> Similar could apply to other special modes, maybe even to most modes
> derived from `special-mode'.

As you point out, there's a lot of modes that only make sense in certain
limited contexts, and having them be interactive isn't very helpful.
I'm not sure it's that much of a problem in general, but it is a
particular an issue with `shell-mode', since I'd guess that a lot of
people type that instead of `M-x shell-script-mode' when starting to
write new shell scripts.

The following fixes this particular issue.  Would something like this be
welcome?

A different fix would be to extend defined-derived-mode to take a
:noninteractive flag to just not include the `(interactive)' in the
defun.  It looks fairly straightforward to implement -- is that a better
idea, perhaps?

(That is, if we want to fix this at all.)

diff --git a/lisp/shell.el b/lisp/shell.el
index 2914d1d2c8..ba7515e7ba 100644
--- a/lisp/shell.el
+++ b/lisp/shell.el
@@ -553,6 +553,8 @@ shell-mode
 `comint-scroll-to-bottom-on-input' and `comint-scroll-to-bottom-on-output'
 control whether input and output cause the window to scroll to the end of the
 buffer."
+  (when (called-interactively-p 'any)
+    (error "Can't be called interactively; did you mean `shell-script-mode' instead?"))
   (setq comint-prompt-regexp shell-prompt-pattern)
   (shell-completion-vars)
   (setq-local paragraph-separate "\\'")

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no