Re: Lisp primitives and their calling of the change hooks

[Stefan Monnier]

> I've found a discrepancy.  Just one.  In (transpose-regions 1 10 11 20),
> the hook calls are, in order, ((1 10) (11 20) (1 20 19)).  The two
> consecutive b-c-f's happen when the two regions are of equal size and
> non-contiguous.

Sounds like a bug alright.

> The cause of this is not hard to find: in Ftranspose_region, editfns.c
> L5204, there are two calls to modify_text on consecutive lines.  This
> seems to be some sort of optimisation.  It is not done elsewhere in
> Ftranspose_region.  I dare say this could be fixed easily.

Feel free to fix it (on master).

> Perhaps for Emacs-27, if we want to fix transpose-regions.

AFAIC this text can be installed in emacs-26 even if there's still a known
bug where we don't behave as promised.  For all we know, there are yet
more (not yet known) such bugs anyway.


        Stefan