Proposal: directory-slash in library names

Proposal: directory-slash in library names

[Tom Breton (Tehom)]

***** Rationale

Emacs library names are restricted to a flat-level namespace.  There
is no explicit support of submodules.

This limitation is usually worked around by using the format
COMMONPREFIX-LIBRARY.  This is used by packages such as org, calc, cl,
and sometimes by non-package arrangements such as pcomplete, which
standardizes the prefix "pcmpl-" for its clients.  Compare it to
Perl's easy deployment of constructions like
"AI::ExpertSystem::Advanced::KnowledgeDB::Base"

This workaround has disadvantages, including:
 * It's effectively limited to 2 components, since names must not
   clash on filesystems that limit filenames to 8.3 format.
 * Those components have to be fairly short.
 * Being short, those components are less readable than they could
   be.
 * Because they have so few characters to work with, library authors
   have to unduly concern themselves with possible nameclashes.
 * It lacks a natural way of naming support files (such as tests) in
   relation to the libraries they support.
 * Module names contain less information about the module's role than
   they could.

***** Proposal

This is real easy, almost a no-op.  I'm not proposing any new code.
I'm not proposing that any existing libraries be rewritten or renamed.

I'm only proposing:

 * to give the official OK to directory-slash in library names, for
   example:

   : dir1/dir2/feature

 * for the directory-slash to be treated as it is in filenames
   (specifically, internally canonized filenames).  Eg the example
   would mean to look for "dir1" anywhere in load-path, for "dir2"
   within that, and for "feature.elc" or "feature.el" there, using the
   first successful match.


***** It already seems to work

I experimented and it already does the right thing on GNU/Linux.  One
can write:

: (require 'dir1/dir2/feature)

and emacs will load-file "feature.el" from "dir1/dir2" beneath any
directory in load-path.

I cannot test it on other systems, but from the C source, it seems as
though it will work on any system that `expand-file-name' works on.
That apparently translates dir separators, eg it calls
CORRECT_DIR_SEPS for WIN_NT.


	Tom Breton (Tehom)

Re: Proposal: directory-slash in library names

[Eli Zaretskii]

> Date: Wed, 6 Jan 2010 18:08:15 -0500
> From: "Tom Breton (Tehom)" <tehom@panix.com>
> 
> 
> I experimented and it already does the right thing on GNU/Linux.  One
> can write:
> 
> : (require 'dir1/dir2/feature)
> 
> and emacs will load-file "feature.el" from "dir1/dir2" beneath any
> directory in load-path.
> 
> I cannot test it on other systems, but from the C source, it seems as
> though it will work on any system that `expand-file-name' works on.
> That apparently translates dir separators, eg it calls
> CORRECT_DIR_SEPS for WIN_NT.

Not only does it work on all platforms, we already use it with CEDET.
So if you needed an official blessing, you already have it, I think.

Re: Proposal: directory-slash in library names

[Richard Stallman]

     * to give the official OK to directory-slash in library names, for
       example:

       : dir1/dir2/feature

If we do this, we might want to set up a systematic way to explicitly
label those directories that should be in the search path.
In a case like, this, you wouldn't want (load "foo")
to searchfor dir1/foo or dir1/dir2/foo.

Re: Proposal: directory-slash in library names

[Tom Breton (Tehom)]

>      * to give the official OK to directory-slash in library names, for
>        example:
>
>        : dir1/dir2/feature
>
> If we do this, we might want to set up a systematic way to explicitly
> label those directories that should be in the search path.
> In a case like, this, you wouldn't want (load "foo")
> to searchfor dir1/foo or dir1/dir2/foo.

Oh, I see.  You want a way to ensure that directories that contain
libraries with names like `dir1/foo' are not directly in the load-path. 
Good catch.  Perhaps a "magic" filename similar to ".nosearch"?

Tom Breton (Tehom)

Re: Proposal: directory-slash in library names

[MON KEY]

> If we do this, we might want to set up a systematic way to explicitly
> label those directories that should be in the search path.
> In a case like, this, you wouldn't want (load "foo")
> to searchfor dir1/foo or dir1/dir2/foo.

In lieu of the other recent discussions of a `package' system for Emacs, please
consider the use of `.' with `qualified' domains at the root of any such feature
e.g. "org.gnu.feature" as opposed "dir/foo/feature" strip the domain
accordingly:

(defun get-the-right-feature (good-feature &optional good-source &rest
bag-o-sources)
  (let (pkg)
    (mapc #'(lambda (bos)
              (let ((myb-good (split-string-and-unquote bos "\\."))
                    is-good)
                (when (memq good-feature
                            (progn
                              (while myb-good (push (read (pop
myb-good)) is-good))
                              is-good))
                  (push (nreverse is-good) pkg))))
          bag-o-sources)
    (let (the-sauce)
      (when good-source
        (mapc #'(lambda (sauce)
                  (let ((is-sauce (memq good-source sauce)))
                  (when is-sauce (setq the-sauce sauce))))
              pkg))
      (cond (the-sauce (memq good-source the-sauce))
            ((= (length pkg) 1) (cdar pkg))
            (t pkg)))))

(get-the-right-feature 'feature 'gnu  "org.gnu.feature"
"org.emacsmirror.bubba"  "com.tromey.feature")
;=> (gnu feature)

(get-the-right-feature 'bubba nil "org.gnu.feature"
"org.emacsmirror.bubba"  "com.tromey.feature")
;=>  (emacsmirror bubba)

(get-the-right-feature 'feature nil "org.gnu.feature"
"org.emacsmirror.bubba"  "com.tromey.feature")
;=> ((com tromey feature) (org gnu feature))

(get-the-right-feature 'feature nil "org.gnu.feature"
"org.emacsmirror.feature"  "com.tromey.feature")
;=> ((com tromey feature) (org emacsmirror feature) (org gnu feature))

(get-the-right-feature 'bubba 'gnu "org.gnu.feature"
"org.emacsmirror.feature"  "com.tromey.feature")
;=> nil

(get-the-right-feature 'feature nil "org.gnu.feature"
"org.emacsmirror.feature/funky"  "com.tromey.feature")
;=> ((com tromey feature) (org gnu feature))