Custom themes and simple variables

[Ralf Angeli <angeli@caeruleus.net>]

Hi,

in AUCTeX we've traditionally had files one could `require' to enable
various settings for different TeX systems and platforms.  For example
if the user loaded tex-mik.el the viewer Yap provided by MiKTeX would be
configured to be used for previewing DVI files instead of xdvi.

I thought something like this could be handled in a more flexible way
with custom themes.  However, it seems that variables defined with
`defvar' in contrast to `defcustom' are not supported because the
`defvar' statement "overwrites" the value set by an active theme.

Here is a simple test case:

$ echo "(deftheme foo \"foo theme\") (custom-theme-set-variables 'foo '(foo \"original\")) (provide-theme 'foo)" > foo-theme.el
$ emacs -Q --eval "(progn (add-to-list 'load-path \".\") (load-theme 'foo) (defvar foo \"changed\") (describe-variable 'foo))"

The first command defines a theme called "foo" and writes it to disk as
the file foo-theme.el.  The second command calls Emacs, tells it to load
the theme, define the variable `foo' (for which the theme also contains
a value) and show the value of it.  This will be "changed".  If you do
the same thing using `defcustom' instead of `defvar' the value will be
"original".

I assume the problem is due to a variable defined with `defvar' not
being supported by the Custom machinery, so this is likely not a bug.
Would there nevertheless be a possibility to handle such variables
cleanly with custom themes?

-- 
Ralf