bug#29110: 25.2; Should push-mark allow duplicates?

[Drew Adams <drew.adams@oracle.com>]

> I understand there might be some use cases, I just don't see which one.
> 
> > Consider the simple case of someone using vanilla `C-u C-SPC'.
> > Someone might want to have duplicates at different positions
> > in the ring, visiting them in order.
> 
> Hmm, I'm tempted to say "bof" too here :)  You are not saying 
>_why_ the user would like to see duplicates.

What part of "visiting them in order" wasn't clear?

That's the point of having a sequence (or ring): order
and (possibly) duplicates.

> >> - Functions working with rings will probably want to remove the
> >> duplicates, so they end up calling `remove' and the like over and over
> >> again.
> >
> > Why "over and over again"?  You can prevent adding duplicates, no?
> 
> In every function calling push-mark, yes.  That's what I mean with "over
> and over again".  How do you prevent this without advising push-mark?

Advising `push-mark' is fine, if that's what you always want,
everywhere.  If not, define your own `my-push-mark` for the
use cases you have.

> But consider this: with Evil, jumping between two marks (so just
> navigating between them) will duplicate each mark every time.

Then there is something wrong with Evil, perhaps.
With vanilla Emacs, jumping to a marker does not push
another marker there.

> You might argue that this is bad code on Evil's side.

I might, if I understood it more.  I really have no idea.

> But then high-level functions might call the jumping
> functions in loops...  And so on.

And so on sounds like compounding a problem.  Is it a problem
of Evil's own making?  Why would it push a mark each time it
jumps to a marker.  Vanilla Emacs doesn't do that.