bug#23648: [PATCH] `defun-declarations-alist' can be unintentionally modified

[Dmitry Gutov]

On 07/18/2016 06:00 AM, npostavs@users.sourceforge.net wrote:

> > Here `delete-dups' destructively modifies a list that includes
> > `defun-declarations-alist' as its tail verbatim, not as a copy.
> > Attached patch should fix that.
>
> I agree with analysis and patch here.

I like the patch as well. Maybe it would be better to use 
cl-remove-duplicates with nconc instead (the use of nil is a little 
non-obvious), but that would require having cl-lib loaded at runtime, 
and elisp-mode depending on it.

In any case, the proposed patch looks safe.