Re: substitute-in-file-name and "$"

[Luc Teirlinck]

Michael Albinus wrote:

   There is no rule that substitute-in-file-name must be called only
   once.

Even if this rule is not stated explicitly, this just seems to be
common sense.  It would appear that this is just a special case of the
general rule that one should avoid bugs.

   For example, if you use partial-completion-mode, the filename in
   the minibuffer will be passed through substitute-in-file-name by
   PC-do-completion. Later file name operations which call internally
   substitute-in-file-name will fail therefore.

To me, it would seem obvious that this is a bug in `PC-do-completion'.
It can not handle filenames containing a literal `$'.

You say "for example".  Are you aware of tons of similar bugs
throughout the Emacs code or is `PC-do-completion' an isolated
example?

   What I'ld like to know: Is it a general rule, that
   substitute-in-file-name can be called only once for a given file name?
   Then it should be documented in the Elisp manual, and it is a bug in
   PC-do-completion. Or is it a more general design problem?

It might actually be good to mention this potential trap in the Elisp
manual.  However, this is a matter of avoiding bugs, not a matter of
following some stylistic "rule".

Sincerely,

Luc.