The replace-{string,regexp}-in-region functions can throw an error if
the replacement text is large compared to the replaced text: (point)
might move beyond END, which means the underlying {,re-}search-forward
functions are called with BOUND "on the wrong side of point".

Recipe from emacs -Q:

1. Open *scratch* and type:
(with-temp-buffer
  (insert "foo bar baz")
  (replace-regexp-in-region
   "ba." "quux corge grault" (point-min) (point-max)))
2. C-j

Backtrace attached, with suggested patch (including tests) to update END
to reflect the displacement after each replacement.

I'm assuming these are the semantics we prefer, since users can't call
these functions with (> end (point-max)) to guard against that error,
but we could also just bail as soon as (> (point) end).  That would
prevent the error, but it could cause us to return early and miss some
matches.

The patch does change the semantics in the opposite situation (and the
tests check for the new behaviour): when the replacement is shorter than
the original text, it is currently possible for matches that were
originally beyond END to become reachable; the patch prevents that.  I'm
assuming that's TRT because if users say "replace no further than
THERE", they're probably talking about a point of interest (end of a
line, a function…) rather than the numeric value of THERE.


If we want this change to go in: should we call it out in the docstrings
and/or "(elisp) Search and Replace" and/or in NEWS?

FWIW: I've seen no regression with a full "make check", but I've just
written the patch, so I haven't had the time to live with it and see
what breaks.


In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.34, cairo version 1.16.0) of 2022-09-10 built on amdahl30
Repository revision: 433fc8bebfef40130bf62f17e5349560b62e566e
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