[armedbear-devel] #P serialization across Windows/non-Windows (was Re: r12666 breaks ASDF compilation on Linux)

[Mark Evenson]

On 6/15/10 2:05 PM, Alessio Stalla wrote:

[…]

> Eliminating the problem in the general case is harder and we'd better
> discuss the possible solutions. Here's my take at it:
>
> 1) don't fix it. State clearly that literal pathnames in source are
> OS-dependent.
>
> 2) keep, for each pathname constructed via #P or parse-namestring, the
> string passed by the user, until the pathname is destructively
> modified. When dumping it, use that string if available, else warn and
> use a calculated string.

I still don't understand how this approach solves the problem with ASDF. 
  Wouldn't we still have the failure on non-Windows when "\foo\bar" is 
passed to the #P reader?  Namely, that it would be interpreted as:

    {
      directory: nil,
      name: "\foo\bar"
    }

What is the point of the "destructively modified" condition?

> 3) dump-object for pathnames outputs a MAKE-PATHNAME form that
> reconstructs the pathname component by component.

I was thinking about

4)  Code a heuristic in the Pathname.init(String) that attempts to 
interpret a Pathname from the other platform by converting all '\' to 
'/'.  Add something

a)  If the Pathname begins with '\\'
     i) if win interpret as UNC server
     ii) non-win signal a CONDITION

b)  convert all '\' to '/'

c)  run the rest of the current init()

On win, the init() code (line 403++) will convert the '\' back to '/'.

A problem arises for non-win Pathnames that contain true '\' characters 
in a directory/file name, which then will have no pathname<-->namestring 
roundtripping.  It should still be possible to construct such shaggy 
monsters via MAKE-PATHNAME.

As for load forms, I think simply marking the namestring as "transient" 
(i.e. not persisting it) will do the right thing as on first access it 
will be re-computed to the proper local conventions.

This still doesn't completely address the presence of win-specific 
Pathname components (HOST with a UNC server, DEVICE with a single 
character string [A-Z]) in non-win.   Signal a CONDITION when this is 
detected?

N.B.  All the above written without benefit of testing with ABCL, as my 
wrist still precludes heavy use of Emacs.

-- 
"A screaming comes across the sky.  It has happened before, but there
is nothing to compare to it now."