bug#43609: 28.0.50; eldoc-documentation-function

[Dmitry Gutov <dgutov@yandex.ru>]

Hi Martin,

On 25.09.2020 11:46, martin rudalics wrote:
> When with emacs -Q I put the following snippet into *scratch*
> 
> (defun foo ()
>    (ignore))
> 
> move point to somewhere on "foo" and do
> 
> M-: (funcall eldoc-documentation-function)
> 
> I get the following backtrace:
> 
> Debugger entered--Lisp error: (void-function nil)
>    nil(:patient)
>    eldoc--make-callback(:patient)
>    eldoc-documentation-default()
>    funcall(eldoc-documentation-default)
>    eval((funcall eldoc-documentation-function) t)
>    eval-expression((funcall eldoc-documentation-function) nil nil 127)
>    funcall-interactively(eval-expression (funcall 
> eldoc-documentation-function) nil nil 127)
>    call-interactively(eval-expression nil nil)
>    command-execute(eval-expression)
> 
> If I do the same thing with Emacs 27 I get
> 
> #("defun: (NAME ARGLIST &optional DOCSTRING DECL &rest BODY)" 0 5 (face 
> font-lock-keyword-face) 8 12 (face eldoc-highlight-function-argument))

You might want to read the docstring for eldoc-documentation-functions, 
in particular the part where "Each hook function is called with at least 
one argument CALLBACK".

I agree that the latest changes make Eldoc gratuitously more complex, 
though. You can read bug#41531, where they started.