bug#62731: 29.0.60; diff-apply-hunk doesn't work for creating new files

[Dmitry Gutov <dmitry@gutov.dev>]

On 02/10/2024 22:41, Eli Zaretskii wrote:

>> With Hg, the format look like this:
>>
>>     diff -r df0ef194120b -r 2039b18843da accessible/aom/AccessibleNode.cpp
>>
>> No mention of 'Hg', that is. Could we match "\`diff -r" and
> 
> If Hg doesn't prepend fake leading directories, we don't need to be
> bothered by Hg.

It does. A fuller example, with deletion:

diff -r d045d1125783 -r 9396bae6ff0d CLOBBER.new
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/CLOBBER.new	Fri Dec 15 20:37:14 2023 +0200
@@ -0,0 +1,56 @@

>>> Also, what about the opposite case, when NEW is /dev/null? does that
>>> work correctly?
>>
>> Not currently or with the proposed patch. It could be fixed along
>> similar lines, but I'm not clear on the ideal behavior here. Delete the
>> "old" file and kill its buffer? And say that with 'message'?
> 
> Something like that, yes.  We could also delete the file silently.

I'm concerned the user is going to wonder whether anything happened at 
all, and checking is a non-trivial action. But if you think this is 
fine, I guess it's something to try.

>> Deleting files is something that one can do manually, though, so solving
>> this seems lower priority.
> 
> When you apply a large set of diffs in which one file is deleted,
> there's no easy way of knowing you should deleted that file.

In the current version of code you will be asked midway through a file 
(or right away, when using diff-apply-hunk) to specify a file name, 
defaulting to /dev/null, and after you press C-g after seeing the odd 
prompt the hunk won't be applied. So it's hard to miss, at least.