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Re: Add a predicate for canonical file name

From: Eli Zaretskii
Subject: Re: Add a predicate for canonical file name
Date: Mon, 12 Sep 2016 20:13:27 +0300

> From: Tino Calancha <address@hidden>
> Date: Mon, 12 Sep 2016 17:23:03 +0900 (JST)
> Cc: address@hidden
> i dont see in Emacs a predicate for a file name being canonical.

Keeping in mind that just running a file name through expand-file-name
will guarantee an absolute (and "canonical") file name as result, what
problem would such a predicate solve that invoking expand-file-name
doesn't?  Especially given that your implementation calls
expand-file-name anyway?

> We have a predicate for absolute file names, `file-name-absolute-p'.

I personally never had a problem with the notion of "absolute file
name".  Yes, file names like "~/foo/bar" and "~user/foo" cause
file-name-absolute-p to return non-nil, but this is so obscure and
marginal feature that I doubt many Lisp programmers even remember

> (defsubst myfile-name-canonical-p (filename)
>    "Return non-nil if FILENAME specifies an absolute canonical file name."
>    (string= filename (expand-file-name filename)))

Using string= here will cause false negatives, e.g. with Windows file
names that use backslashes vs forward slashes, or due to letter-case
differences on case-insensitive file systems.  Did you really mean

But anyway, the need for this is not clear to me.


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