bug#36372: 27.0.50; replace-regexp-in-string skips START first chars in return value [PATCH]

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Wed, 26 Jun 2019 11:31:01 +0200, Mattias Engdegård <mattiase@acm.org> said:

    Mattias> 25 juni 2019 kl. 17.26 skrev Eli Zaretskii <eliz@gnu.org>:
    >> 
    >>> The question is whether it is too late to fix the bug, or if it needs to be documented.
    >> 
    >> Both, I think ;-)

    Mattias> Documenting a bug rather than fixing it never feels very satisfactory, but it may be the lesser evil.
    Mattias> What about this patch?

I think this is one of those 'who could possibly be relying on this
behaviour' bugs that bites you hard if you change things, so
documentation is probably best. Minor nits below

    Mattias> From d5419cbf491cccb91843b8e3d6270df1c40a9004 Mon Sep 17 00:00:00 2001
    Mattias> From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
    Mattias> Date: Wed, 26 Jun 2019 11:23:32 +0200
    Mattias> Subject: [PATCH] Document bug in `replace-regexp-in-string'

    Mattias> `replace-regexp-in-string' omits the first START characters of the
    Mattias> input string in its return value.  This is a clear bug, but fixing it
    Mattias> probably causes more trouble; document the behaviour instead (bug#36372).

    Mattias> * doc/lispref/searching.texi (Search and Replace)
    Mattias> * lisp/subr.el (replace-regexp-in-string):
    Mattias> Document current behaviour.
    Mattias> ---
    Mattias>  doc/lispref/searching.texi | 4 ++--
    Mattias>  lisp/subr.el               | 3 ++-
    Mattias>  2 files changed, 4 insertions(+), 3 deletions(-)

    Mattias> diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi
    Mattias> index 33455114da..86a907021c 100644
    Mattias> --- a/doc/lispref/searching.texi
    Mattias> +++ b/doc/lispref/searching.texi
    Mattias> @@ -1790,8 +1790,8 @@ Search and Replace
    Mattias>  This function copies @var{string} and searches it for matches for
    Mattias>  @var{regexp}, and replaces them with @var{rep}.  It returns the
    Mattias>  modified copy.  If @var{start} is non-@code{nil}, the search for
    Mattias> -matches starts at that index in @var{string}, so matches starting
    Mattias> -before that index are not changed.
    Mattias> +matches starts at that index in @var{string}, and the returned value
    Mattias> +does not include first @var{start} characters of @var{string}.

insert 'the' before 'first'

    Mattias>  This function uses @code{replace-match} to do the replacement, and it
    Mattias>  passes the optional arguments @var{fixedcase}, @var{literal} and
    Mattias> diff --git a/lisp/subr.el b/lisp/subr.el
    Mattias> index baff1e909a..ba388b3721 100644
    Mattias> --- a/lisp/subr.el
    Mattias> +++ b/lisp/subr.el
    Mattias> @@ -4208,7 +4208,8 @@ replace-regexp-in-string
 
    Mattias>  Optional arguments FIXEDCASE, LITERAL and SUBEXP are like the
    Mattias>  arguments with the same names of function `replace-match'.  If START
    Mattias> -is non-nil, start replacements at that index in STRING.
    Mattias> +is non-nil, start replacements at that index in STRING.  The return
    Mattias> +value then omits the first START characters of STRING.
 
'at that index in STRING, and omit the first START characters from the
return value.'

    Mattias>  REP is either a string used as the NEWTEXT arg of `replace-match' or a
    Mattias>  function.  If it is a function, it is called with the actual text of each
    Mattias> -- 
    Mattias> 2.20.1 (Apple Git-117)