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Re: Question about defcustom and load-history


From: Tassilo Horn
Subject: Re: Question about defcustom and load-history
Date: Sun, 31 Mar 2019 09:13:51 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

Mauro Aranda <address@hidden> writes:

Hi Mauro,

> I noticed that for files that define customizable variables, there's a
> duplicate entry for each one of them.  However, symbols defined with
> 'defvar'
> appear only once.  Does anybody know why is that?

I'm not sure but I'd suspect this code in the end of
`custom-declare-variable'.

--8<---------------cut here---------------start------------->8---
  ;; Use defvar to set the docstring as well as the special-variable-p flag.
  ;; FIXME: We should reproduce more of `defvar's behavior, such as the warning
  ;; when the var is currently let-bound.
  (if (not (default-boundp symbol))
      ;; Don't use defvar to avoid setting a default-value when undesired.
      (when doc (put symbol 'variable-documentation doc))
    (eval `(defvar ,symbol nil ,@(when doc (list doc)))))
  (push symbol current-load-list)
  (run-hooks 'custom-define-hook)
  symbol)
--8<---------------cut here---------------end--------------->8---

In the falsy case, i.e., when the variable has an initial default value,
a `defvar' form is evaled resulting in one entry, and then the symbol is
pushed again to `current-load-list' from where it probably gets to
`load-history'.

I wonder how you could have a non-default-bound custom variable anyway?
Maybe using something like

  (defvar foo)
  (defcustom foo nil ...)
  
?

Anyway, I have no clue if your observation is itensional or
accidentally...

Bye,
Tassilo



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