Re: (concat "/dir/name/" "foo") --> (expand-file-name "foo" "/dir/name/")

[prj@po.cwru.edu (Paul Jarc)]

Kai.Grossjohann@CS.Uni-Dortmund.DE (Kai Großjohann) writes:
> In the Gnus source code, we often have constructs like this:
> 
>     (concat "/dir/name/" "file-name")
> 
> I think this should be replaced with:
> 
>     (expand-file-name "file-name" "/dir/name/")
> 
> What do you think?

It depends on the contents of "file-name".  If it might contain
something that really needs to be normalized, then it should be handed
to expand-file-name.  If it should be interpreted literally, then
expand-file-name might do something unintended.  Consider, e.g.,
"foo/../bar", where foo is a symlink.

The default maildir in nnmaildir is expressed as
(concat (file-name-as-directory (expand-file-name "~")) "Maildir").
User-supplied maildir names are also normalized once with
expand-file-name, but then after that, dir/file is always accessed
with (concat (file-name-as-directory dir) file).  I think
file-name-as-directory and directory-file-name are idempotent on all
platforms, although they aren't documented as such, AFAICT.  nnmaildir
doesn't depend on their idempotency, as long as user-supplied maildir
names are what would be returned from directory-file-name.


paul