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)