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Re: port-filename and path canonicalization

From: Ludovic Courtès
Subject: Re: port-filename and path canonicalization
Date: Thu, 22 Apr 2010 14:50:57 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)


Andy Wingo <address@hidden> writes:

> On Tue 20 Apr 2010 18:57, address@hidden (Ludovic Courtès) writes:
>>> 2. I think a fluid is still necessary, because a file being
>>> compiled can do an `include' or `include-from-path', or even
>>> `open-input-file' in a macro, and all these cases you would want the
>>> same %file-port-name-canonicalization to take effect.
>> Indeed, this one is tricky.
>> I still think it’s application-specific, though.  How about calling the
>> fluid, say, %compiler-file-name-canonicalization instead?  :-)
> Are you proposing that all file-opening functions check the
> %compiler-file-name-canonicalization fluid?

No, I’m talking about file-opening functions of the compiler, which
include ‘compile-file’, ‘include’, etc.

> If you build out-of-source, you might end up with
>   guile-tools compile -o ice-9/boot-9.go ../../modules/ice-9/boot-9.scm
> So the file you open is "../../modules/ice-9/boot-9.scm", but you want
> to give it a "relative canonicalization" -- in this case
> "ice-9/boot-9.scm" is the canonicalization of
> ../../modules/ice-9/boot-9.scm, *relative* to "../../modules" (or indeed
> to "/home/wingo/src/guile/modules").

OK, understood.

>>> So you'd have to do a set-port-filename! on the port, mucking up your
>>> code -- and how would you decide what to set? In N places you'd have to
>>> duplicate fport_canonicalize_filename, and you'd probably have to make
>>> scm_i_relativize_path public.
>> I failed to get the transition at “So”.  :-)
>> What does scm_i_relativize_path do?  (It lacks a leading comment, hint
>> hint.  ;-))

BTW, my understanding is that scm_i_relativize_path does lexical
“relativization”, which doesn’t work on POSIX and GNU systems where ‘..’
resolution is /not/ lexical.  (See
<> for details.)

The following should work:

--8<---------------cut here---------------start------------->8---
(define (relativize-path path dir)
  ;; Return PATH relative to DIR or #f on failure.
  (let ((path (canonicalize-path path))
        (dir  (canonicalize-path dir)))
    (and=> (string-prefix-length dir path)
           (lambda (start)
             (substring path (+ 1 start) (string-length path))))))

scheme@(guile-user)> (relativize-path "../guile/module/ice-9/boot-9.scm" 
scheme@(guile-user)> (relativize-path "module/ice-9/boot-9.scm" 
--8<---------------cut here---------------end--------------->8---

It still does lexical relativization but does so after canonicalization
of both arguments.

> you would have to do:
>   (define (open-input-file* path)
>     (let ((p (open-input-file path)))
>       (case (fluid-ref %file-port-name-canonicalization)
>         ((absolute)
>          (set-port-filename! p (canonicalize-path path)))
>         ((relative)
>          (set-port-filename! p (relativize-path (canonicalize-path path) 
> %load-path))))
>       p))
> which is a bit ugly; e.g. include-from-path would need to do this, as
> would any third-party equivalent of include-from-path, and even
> down to the open-file level. Yuk.

Wouldn’t it suffice if only ‘compile-file’, ‘include’, and
‘include-from-path’ relativize paths?


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