defcustom-c-stylevar rewrite: 2nd rfc

[Thien-Thi Nguyen <ttn@gnuvola.org>]

clearing the plate...

i posted for comment a few weeks (~month?) back the appended
rewrite of `defcustom-c-stylevar'.  no response.  this is a
second call for comment after which time (in a week) if there
are no objections i will commit it on the trunk.

thi

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(defmacro defcustom-c-stylevar (name val doc &rest args)
  "Define a style variable NAME with VAL and DOC.
More precisely, convert the given `:type FOO', mined out of ARGS,
to an aggregate `:type (radio STYLE (PREAMBLE FOO))', append some
some boilerplate documentation to DOC, arrange for the fallback
value of NAME to be VAL, and call `custom-declare-variable' to
do the rest of the work.

STYLE stands for the choice where the value is taken from some
style setting.  PREAMBLE is optionally prepended to FOO; that is,
if FOO contains :tag or :value, the respective two-element list
component is ignored."
  (declare (debug (symbolp form stringp &rest)))
  (let* ((expanded-doc (concat doc "

This is a style variable.  Apart from the valid values described
above, it can be set to the symbol `set-from-style'.  In that case,
it takes its value from the style system (see `c-default-style' and
`c-style-alist') when a CC Mode buffer is initialized.  Otherwise,
the value set here overrides the style system (there is a variable
`c-old-style-variable-behavior' that changes this, though)."))
         (typ (eval (plist-get args :type)))
         (type (if (consp typ) typ (list typ)))
         (head (car type))
         (tail (cdr type))
         (newt (append (unless (plist-get tail :tag)
                         '(:tag "Override style settings"))
                       (unless (plist-get tail :value)
                         `(:value ,val))
                       tail))
         (aggregate `'(radio
                       (const :tag "Use style settings" set-from-style)
                       ,(cons head newt))))
    `(progn
       (c-set-stylevar-fallback ',name ,val)
       (custom-declare-variable
        ',name ''set-from-style
        ,expanded-doc
        ,@(plist-put args :type aggregate)))))