Re: [Emacs-diffs] master 7466a4d: Cygwin emacsclient handles w32 file names

[Ken Brown <kbrown@cornell.edu>]

On 6/29/2015 10:40 PM, Ken Brown wrote:
> On 6/29/2015 8:59 PM, Michael Mauger wrote:
>> branch: master
>> commit 7466a4ded6ded0bea50151395b7a0fccc5dfd167
>> Author: Michael R. Mauger <michael@mauger.com>
>> Commit: Michael R. Mauger <michael@mauger.com>
>>
>>      Cygwin emacsclient handles w32 file names
>> ---
>>   lisp/server.el |    3 +++
>>   1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/lisp/server.el b/lisp/server.el
>> index 2007635..ce19b3c 100644
>> --- a/lisp/server.el
>> +++ b/lisp/server.el
>> @@ -1167,6 +1167,9 @@ The following commands are accepted by the client:
>>                    (let ((file (pop args-left)))
>>                      (if coding-system
>>                          (setq file (decode-coding-string file
>> coding-system)))
>> +                   (when (and (eq system-type 'cygwin)
>> +                              (fboundp
>> 'cygwin-convert-file-name-from-windows))
>
> There's no need for the 'fboundp ...' here;
> cygwin-convert-file-name-from-windows is defined in all Cygwin builds.
>
>> +                     (setq file
>> (cygwin-convert-file-name-from-windows file)))
>>                      (setq file (expand-file-name file dir))
>>                      (push (cons file filepos) files)
>>                      (server-log (format "New file: %s %s"
>
> Are you sure that emacsclient will still handle ordinary Cygwin file
> names properly after this change?  I'm concerned about file names that
> contain characters from the (default) UTF-8 character set.  I'm not very
> familiar with exactly how cygwin-convert-file-name-from-windows works,
> but its name suggests that it should be given a file name that's
> understood by Windows.

I've tested this a little with file names containing UTF-8-encoded 
Chinese and other non-ASCII characters, and it appears to work OK.  But 
I *think* it only works because of accidental implementation details of 
cygwin-convert-file-name-from-windows (and the underlying Cygwin 
function cygwin_conv_path).  Basically, it seems that these functions 
don't actually try to do any conversion if they are given a multibyte 
string instead of the expected UTF-16 string.

So even though this change *might* be harmless, I think it could lead to 
bugs later if implementations change.  I don't think 
cygwin-convert-file-name-from-windows should be called on a file name 
that is not known to be a (UTF-16-encoded) Windows file name.  If you 
look at the (very few) places in the emacs code where that function is 
currently called, you'll see that the argument is indeed known to be a 
Windows file name.

Ken