Re: 900276502f..: Paul Eggert 2018-11-13 Act like POSIX sh if $HOME is relative

["Óscar Fuentes" <ofv@wanadoo.es>]

João Távora <joaotavora@gmail.com> writes:

> On Wed, Dec 12, 2018 at 1:41 PM Óscar Fuentes <ofv@wanadoo.es> wrote:
>
>> "João Távora" <joaotavora@gmail.com> writes:
>>
>> > I've only now caught up with the discussion of bug#33255.  Are the
>> > consequences of interpreting the string "c:" on Windows as a relative
>> > file name understood?
>> >
>> > With HOME="z:", it used to be that (expand-file-name "~/blabla")
>> > returned "z:/blabla" but now it returns
>> > "z:/source/emacs/emacs/src/z:/blabla", which is not a valid Windows
>> > pathname.
>>
>> [snip]
>>
>> I was about to post a reply but Yuri already answered, so I'll only add
>> a pointer to an official reference about this topic:
>>
>> https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats
>>
>
> Óscar, I get it that z:bla has a meaning. But is this meaning ever useful
> when for expanding "~/bla"?
>
> I didn't say the change was "wrong".  I just asked, basically:
>
> * if anyone had contemplated this particular problem on Windows;
> * if it's possible to interpret HOME specially for this particular bit of
> backward compatibility without breaking the cases of bug#33255

I don't know about the motivation of this change and have no time to
study it (a cursory look at the diff shows some concerning points wrt
Windows compatibility such as

        hope one's home directory doesn't contain ':' or '%'.  */

).

A Windows path with no slash after the volume letter is relative and
always was. For the specific case of HOME, I can't think of a sane
scenario where a user could take advantage of interpreting V: as a
relative path for HOME on Emacs, but maybe I'm not being imaginative
enough.

You are asking for being bug-compatible with previous Emacs because you
must cope with bugs on other applications :-) Do you think that this
problem is frequent enough? What applications are those that don't admit
an slash after the volume letter in HOME?