bug#24441: 24.5; rename directory in dired to change case

[Paul Eggert <eggert@cs.ucla.edu>]

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Three comments about that fix.

1. Emacs seems to conflate whether a file system is case-sensitive, and 
whether it is case-preserving. Darwin pathconf distinguishes between 
_PC_CASE_SENSITIVE and _PC_CASE_PRESERVING. For example, perhaps the 
following code in dired-do-create-files:

                (if (and (file-name-case-insensitive-p (car fn-list))
                     (eq op-symbol 'move)
                     dired-one-file

should also check whether (car fn-list) is on a case-preserving file 
system (if not, there's no point going ahead, as the user can't change 
the case anyway). I suppose this would require adding a Lisp predicate 
for _PC_CASE_PRESERVING. (Possibly the MS-Windows code already deals 
with this, and Cygwin and macOS are currently broken.)

2. From my reading of the Apple documentation, the code taken from that 
circa-2007 website should have problems on some file systems. It does 
not match what Wine does in a similar situation.

3. Nowadays, I hope pathconf works on Apple; that's simpler. If not, I 
think the Wine approach should be better. So I installed the attached 
patch to try to do that. If you have access to a case-insensitive file 
system on macOS, please try it out as-is, or compiled with 
-DDARWIN_OS_CASE_SENSITIVE_FIXME=1 or 
-DDARWIN_OS_CASE_SENSITIVE_FIXME=2, and let me know how it works.


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