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bug#8035: Processing of .. in a file path after going thru symlink
From: |
Lars Ingebrigtsen |
Subject: |
bug#8035: Processing of .. in a file path after going thru symlink |
Date: |
Thu, 26 Aug 2021 18:29:54 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
spucci <slpnabble@blackberry-hill.com> writes:
> When emacs attempts to find a file with "../" as a path component, it
> appears to be "smart" about it and simply remove the previous directory path
> (e.g., "foo/bar/../x" gets converted to "foo/x"). But if bar is a symlink,
> then it doesn't properly find the file. So in compiler output, which
> references such files, the next-error function fails to find the file with
> the given name.
>
> mkdir dest
> mkdir dest/subdir
> mkdir src
> ln -s ../dest/subdir src/subdir
> echo "#error This is an error" > dest/foo.c
>
> Now M-x compile, and give it cc -c src/subdir/../foo.c
>
> *compilation* buffer has:
> cc -c src/subdir/../foo.c
> src/subdir/../foo.c:1:2: error: #error This is an error
>
> and do a next-error: Emacs complains it can't find the file.
This is an even more foundational problem:
(file-exists-p "/tmp/comp/src/subdir/../foo.c")
=> nil
(file-truename "/tmp/comp/src/subdir/../foo.c")
=> "/tmp/comp/dest/foo.c"
(file-exists-p (file-truename "/tmp/comp/src/subdir/../foo.c"))
=> t
And this is because:
static Lisp_Object
check_file_access (Lisp_Object file, Lisp_Object operation, int amode)
{
file = Fexpand_file_name (file, Qnil);
I'm guessing it's calling expand-file-name here to resolve "~"? It's
also a micro-optimisation, I guess -- collapsing "parent/.." textually
without checking the file system is very cheap.
But... this does mean that `file-exists-p' and friends are unreliable
in the presence of symlinks, which is pretty depressing. I think that
`expand-file-name' call in check_file_access should be changed to
something that just does the "~" expansion.
Any opinions?
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no
- bug#8035: Processing of .. in a file path after going thru symlink,
Lars Ingebrigtsen <=
bug#8035: Processing of .. in a file path after going thru symlink, Andreas Schwab, 2021/08/26