bug#4515: 23.1.50; Reverting changes on versioned file does not revert vc modeline status

[Óscar Fuentes]

Dan Nicolaescu <dann@ics.uci.edu> writes:

> Óscar Fuentes <ofv@wanadoo.es> writes:
>
>   > Dan Nicolaescu <dann@ics.uci.edu> writes:
>   > 
>   > > ofv@wanadoo.es. "(Óscar" Fuentes) writes:
>   > >
>   > >   > Please write in English if possible, because the Emacs maintainers
>   > >   > usually do not have translators to read other languages for them.
>   > >   > 
>   > >   > Your bug report will be posted to the emacs-pretest-bug@gnu.org 
> mailing list.
>   > >   > 
>   > >   > Please describe exactly what actions triggered the bug
>   > >   > and the precise symptoms of the bug:
>   > >   > 
>   > >   > When a modified versioned file is edited in such a way that the
>   > >   > modifications undoes previous changes to the file, after saving it 
> the
>   > >   > VC-dired buffer for the working copy is automatically updated 
> showing
>   > >   > that the status of the file is "up to date", but the VC modeline 
> for the
>   > >   > buffer that visits the file does not change and keeps indicating 
> that
>   > >   > the file state is "locally modified".
>   > >
>   > > Can you please describe step by step the actions necessary to reproduce
>   > > this starting from emacs -Q?
>   > 
>   > emacs -Q
>   > 
>   > C-x C-f some-versioned-unmodified-file
>   > do some edition
>   > C-x C-s (the VC status modeline indicator changes from `-' to `:')
>   > undo previous edition
>   > C-x C-s
>   > 
>   > Now you just turned the file to its original state and is unmodified as
>   > far as the version control system is concerned, but the VC modeline
>   > keeps showing `:' (for example Bzr:836) indicating that the file is
>   > edited. After saving a versioned file, VC should check if the VC backend
>   > flags the file as edited and update the modeline accordingly.
>
> You can do M-x revert-buffer or C-x v u and that would reset the VC
> state accordingly.

Yes, I know.

> Checking for this condition after each save is prohibitively expensive,
> and it's an extremely rare event, so it's not worth optimizing for.

Automatically checking the VC state after each save is actually
performed if there is a vc-dired buffer for the working copy where the
file resides. That check updates the vc-dired with the correct state of
the saved file.

Part of my job is experimenting tweaks and micro-improvements on
existing code bases. After every session I end with lots of buffers
showing the "edited" vc modeline indicator when in fact only one or two
are effectively edited. This renders useless the vc state indicator and
turns its meaning into "When `:' is shown, this file was edited, but it
may be up-to-date now".

> So this is neither a bug, not something worth improving.

Well, the vc status on the modeline is showing the wrong state.

Would you accept a patch that implements an option for checking after
every save and updating the vc state on the modeline accordingly?

-- 
Óscar