bug#51809: 29.0.50; [PATCH] Support for outline default state in Diff buffers

[Juri Linkov]

>> Something strange happened recently with diff-mode and outline-minor-mode.
>> I can't use this combination anymore.  While reading your patches, I'm trying
>> to type TAB on the hunk header to hide already viewed hunks of your patch.
>> But TAB does nothing now.  Do you see the same?  TAB is used to hide/show 
>> body
>> when outline-minor-mode-cycle is t.
>
> I've observed too that `outline-minor-mode-cycle' didn't worked well in
> `diff-mode' buffers but I never saw it working!
>
> Since I am used to hitting TAB to go to next button or for completion,
> and I am used to the horrible `outline-minor-mode-prefix' bindings, my
> feeling is that TAB was a bad choice for this, and I didn't try to
> debug: I just turned off `outline-minor-mode-cycle'...

TAB is not a problem when `outline-minor-mode-cycle-filter'
is customized to allow outline's TAB only on some parts
of the outline heading, e.g. only at the beginning,
or everywhere except the beginning of the diff hunk line.
Then typing TAB everywhere else will go to the next button.

> Do you have `diff-font-lock-prettify' enabled? I remember the situation
> was better without this, not sure...

Nope, `diff-font-lock-prettify' is disabled.