[asdf-devel] Guard against (push "/foo/bar" asdf:*central-registry*)

[Daniel Herring]

2009/7/10 Stelian Ionescu <sionescu at cddr.org>:
> On Tue, 2009-07-07 at 12:31 +0200, Tobias C. Rittweiler wrote:
>> I think it's bitten pretty much all of us that we at least once tried to
>> push a non-directory-designating filename to *CENTRAL-REGISTRY*.
>>
>> It's a common pitfalls for newcomers.
>>
>> Couldn't ASDF signal a warning when it encounters such a thing while
>> grovelling through the registry?
>
> Why not simply deprecate(or unexport *CENTRAL-REGISTRY*) and add a
> function REGISTER-ASDF-DIRECTORY that does all necessary checks ?

I like the idea of adding a helper function.

I don't like the idea of hiding *CENTRAL-REGISTRY*.  Given that asdf needs 
a well-ordered list of directories to traverse (a la PATH on every major 
OS), the current exported list provides a powerful API.


Here's an actual case which greatly benefits from the registry being an 
exported special variable.

(let ((*central-registry* (list only-search-here)))
  (if (asdf:operate 'asdf:load-op :test-package)
      test-package-found-where-expected
      error))


Here's a quick sketch of two helpers that should handle most common uses.

(defun register-directory (path &optional (where :last) other)
  (validate-or-die path)
  (when other
    (find-or-die other *central-registry*))
  (when (find path *central-registry :test #'same-path)
    (return))
  (setf *central-registry*
        (ccase where
          (:first
           (cons path *central-registry*))
          (:last
           (append *central-registry* (list path)))
          (:before
           (append paths-before-other
                   (list path other)
                   paths-after-other))
          (:after
           (append paths-before-other
                   (list other path)
                   paths-after-other)))))
(defun deregister-directory (path)
  (setf *central-registry*
        (remove path *central-registry*)))


Later,
Daniel