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bug#15718: 24.3.50; `C-M-x' does not work, with `defcustom' inside `when


From: Lars Ingebrigtsen
Subject: bug#15718: 24.3.50; `C-M-x' does not work, with `defcustom' inside `when'
Date: Wed, 14 Aug 2019 19:57:02 -0700
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

Drew Adams <address@hidden> writes:

> emacs -Q
>
> (when t
>   (defcustom foo nil
>    "..."
>    :type boolean))
>
> M-x set-variable foo t
>
> Put point on foo in the defcustom sexp, and do `C-M-x'.  `foo' is echoed
> in the echo area, giving you the impression that the defcustom was
> reevaluated, reinitializing `foo'.
>
> C-h v foo ;; => t, not nil.
>
> Without the `when', i.e., with the `defcustom' at top level, the value
> is nil, as a user would expect.

I think this works as documented:

--
Evaluate the top-level form containing point, or after point.

If the current defun is actually a call to ‘defvar’ or ‘defcustom’,
evaluating it this way resets the variable using its initial value
expression (using the defcustom’s :set function if there is one), even
if the variable already has some other value.  (Normally ‘defvar’ and
‘defcustom’ do not alter the value if there already is one.)
--

So only if the def* is top-level does the magic DWIM value-setting thing
happen.

Closing.

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





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