Re: Removing rollback from VC mode - request for comment

[Jonas Bernoulli]

Eli Zaretskii <address@hidden> writes:

>> Nicolas Richard <address@hidden> writes:
>> 
>> I don't know what Eli has in mind, but perhaps magit-make-margin-overlay
>> is one such thing ?
>
> Yes, it's one of them.

`elisp(Displaying in the Margins)' states that, "to display something in
the margin _in association with_ certain buffer text, without altering
or preventing the display of that text, put a `before-string' property
on the text and put the margin display specification on the contents of
the before-string."

That's what `magit-make-margin-overlay' does:

  (defun magit-make-margin-overlay (&rest strings)
    (let ((o (make-overlay (point) (line-end-position) nil t)))
      (overlay-put o 'evaporate t)
      (overlay-put o 'before-string
                   (propertize "o" 'display
                               (list '(margin right-margin)
                                     (apply #'concat strings))))))

It seems to me that Magit is doing it the way it is supposed to be doing
it.  Is there another undocumented way?  Am I missing something?

The documentation above does not explicitly mention that an overlay has
to be used, but I could not get it to work otherwise.  There is only one
builtin package which uses `(margin [left|right]-margin)`, Linum-Mode,
and it also uses overlays, in pretty much the same way.

(There is one small difference in that Linum-Mode uses
  (make-overlay (point) (point) ...)
while Magit uses
  (make-overlay (point) (line-end-position))
which is kinda pointless because it unfortunately does not have the
desired effect of keeping to display the margin's text even when
`line-beginning-position' is scrolled of the window.  So yeah, I
could change that).

In summary, yeah this is ugly, but it ain't Magit's fault.

Or do you frown upon Magit making the margin "buffer-local" using
`magit-set-buffer-margin'?

Ps: I am only interested in constructive criticism of Magit's next
branch.  Neither broad "it's all wrong", nor wards which used to existed
in 1.2.* or master interest me.