Thoughts on support for vc-diff unsaved buffer contents?

Thoughts on support for vc-diff unsaved buffer contents?

[Campbell Barton]

Hi, recently I've run into a situation where it's necessary to calculate 
modified line ranges without first saving the buffer (where "modified" 
is determined by a version control diff).

I'm curious if this is something that might be supported - or, is 
already supported (although I'm fairly sure it's not).

The use case is for auto-formatters only to format modified lines.

This particular case is for clang-format.el although the same 
functionality could useful for other formatters too.

clang-format.el can be configured to format on save,
so when saving: clang-format.el calculates the lines that differ from 
the working copy them formats them before saving.

Currently it's necessary for clang-format.el to call git & diff 
directly, which makes the functionality limited to git. I was hoping 
this could be supported in a generic way that uses generic `vc` API's.

Re: Thoughts on support for vc-diff unsaved buffer contents?

[James Thomas]

Campbell Barton wrote:

> Hi, recently I've run into a situation where it's necessary to
> calculate modified line ranges without first saving the buffer (where
> "modified" is determined by a version control diff).
>
> I'm curious if this is something that might be supported - or, is
> already supported (although I'm fairly sure it's not).
>
> ...
>
> so when saving: clang-format.el calculates the lines that differ from
> the working copy them formats them before saving.
>
> Currently it's necessary for clang-format.el to call git & diff
> directly, which makes the functionality limited to git. I was hoping
> this could be supported in a generic way that uses generic `vc` API's.

Isn't it enough to pipe vc-find-revision-no-save of vc-working-revision to
diff? (IIUYC)

--

Re: Thoughts on support for vc-diff unsaved buffer contents?

[Alfred M. Szmidt]

   Hi, recently I've run into a situation where it's necessary to calculate 
   modified line ranges without first saving the buffer (where "modified" 
   is determined by a version control diff).

   I'm curious if this is something that might be supported - or, is 
   already supported (although I'm fairly sure it's not).

Maybe diff-buffer-with-file?

   The use case is for auto-formatters only to format modified lines.

   This particular case is for clang-format.el although the same 
   functionality could useful for other formatters too.

   clang-format.el can be configured to format on save,
   so when saving: clang-format.el calculates the lines that differ from 
   the working copy them formats them before saving.

   Currently it's necessary for clang-format.el to call git & diff 
   directly, which makes the functionality limited to git. I was hoping 
   this could be supported in a generic way that uses generic `vc` API's.

Re: Thoughts on support for vc-diff unsaved buffer contents?

[Juri Linkov]

> Hi, recently I've run into a situation where it's necessary to calculate
> modified line ranges without first saving the buffer (where "modified" is
> determined by a version control diff).
>
> I'm curious if this is something that might be supported - or, is already
> supported (although I'm fairly sure it's not).

'diff-no-select' as well as 'multi-file-diff-no-select' accept
unsaved buffers as their arguments.

Re: Thoughts on support for vc-diff unsaved buffer contents?

[Campbell Barton]

On 24-11-22 6:44 PM, Juri Linkov wrote:
>> Hi, recently I've run into a situation where it's necessary to calculate
>> modified line ranges without first saving the buffer (where "modified" is
>> determined by a version control diff).
>>
>> I'm curious if this is something that might be supported - or, is already
>> supported (although I'm fairly sure it's not).
> 
> 'diff-no-select' as well as 'multi-file-diff-no-select' accept
> unsaved buffers as their arguments.

Thanks for the suggestion.

The part I'm not sure about regarding `diff-no-select' & 
`diff-buffer-with-file' is how they could work with version-control 
(vc-diff or a related functions).

As far as I can see the diff needs to be generated by version-control 
(git/hg/svn etc) instead of a file - since the "original" file 
necessarily exist as a file on disk.