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bug#8035: Processing of .. in a file path after going thru symlink
From: |
Eli Zaretskii |
Subject: |
bug#8035: Processing of .. in a file path after going thru symlink |
Date: |
Thu, 26 Aug 2021 20:30:29 +0300 |
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: slpnabble@blackberry-hill.com, 8035@debbugs.gnu.org
> Date: Thu, 26 Aug 2021 19:24:28 +0200
>
> Eli Zaretskii <eliz@gnu.org> writes:
>
> > expand-file-name also normalizes file names, though. Which is also
> > needed in some use cases, e.g. when the /foo/bar/ isn't accessible,
> > but /foo/ is, in which case failing to normalize /foo/bar/../quux
> > could fail some file I/O function.
>
> Hm, yes, that's a point...
The OP's use case is clearly documented in the ELisp manual:
Note also that ‘expand-file-name’ does not follow symbolic links at
any level. This results in a difference between the way
‘file-truename’ and ‘expand-file-name’ treat ‘..’. Assuming that
‘/tmp/bar’ is a symbolic link to the directory ‘/tmp/foo/bar’ we
get:
(file-truename "/tmp/bar/../myfile")
⇒ "/tmp/foo/myfile"
(expand-file-name "/tmp/bar/../myfile")
⇒ "/tmp/myfile"
If you may need to follow symbolic links preceding ‘..’, you should
make sure to call ‘file-truename’ without prior direct or indirect
calls to ‘expand-file-name’. *Note Truenames::.
So I think we need to use file-truename if we want to support such
uses of symlinks in "M-x compile" etc.
bug#8035: Processing of .. in a file path after going thru symlink, Andreas Schwab, 2021/08/26