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

["Mattias Engdegård" <mattiase@acm.org>]

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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 ;-)

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


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

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

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

diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi
index 33455114da..86a907021c 100644
--- a/doc/lispref/searching.texi
+++ b/doc/lispref/searching.texi
@@ -1790,8 +1790,8 @@ Search and Replace
 This function copies @var{string} and searches it for matches for
 @var{regexp}, and replaces them with @var{rep}.  It returns the
 modified copy.  If @var{start} is non-@code{nil}, the search for
-matches starts at that index in @var{string}, so matches starting
-before that index are not changed.
+matches starts at that index in @var{string}, and the returned value
+does not include first @var{start} characters of @var{string}.
 
 This function uses @code{replace-match} to do the replacement, and it
 passes the optional arguments @var{fixedcase}, @var{literal} and
diff --git a/lisp/subr.el b/lisp/subr.el
index baff1e909a..ba388b3721 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -4208,7 +4208,8 @@ replace-regexp-in-string
 
 Optional arguments FIXEDCASE, LITERAL and SUBEXP are like the
 arguments with the same names of function `replace-match'.  If START
-is non-nil, start replacements at that index in STRING.
+is non-nil, start replacements at that index in STRING.  The return
+value then omits the first START characters of STRING.
 
 REP is either a string used as the NEWTEXT arg of `replace-match' or a
 function.  If it is a function, it is called with the actual text of each
-- 
2.20.1 (Apple Git-117)