Re: i18n/l10n summary

[Paul Eggert <eggert@cs.ucla.edu>]

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Philipp Stephani wrote:
> Wrong example, try (format "%1$c %1$s" ?±)

Ouch. Fixing that (without adversely affecting performance) would be a bit of a 
hassle. Not sure that it's worth it. For now let's just document the limitation. 
I installed the attached.

>> And on further thought, the tradition for Emacs is to
>> document supported behavior and not worry about slowing Emacs down to
>> check for undocumented usage
> 
> Would be great to break that tradition, but that's for another discussion.

Indeed.

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From 0147cdd4d96f1eaeef720ee0b89bddd27eaf4233 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 3 Jun 2017 01:31:04 -0700
Subject: [PATCH] =?UTF-8?q?Document=20uniqueness=20limitation=20of=20?=
 =?UTF-8?q?=E2=80=98format=E2=80=99?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* doc/lispref/strings.texi (Formatting Strings):
* src/editfns.c (Fformat):
Document that field numbers should be unique within a format.
---
 doc/lispref/strings.texi | 7 ++++---
 src/editfns.c            | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index e80e778..f365c80 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -965,9 +965,10 @@ Formatting Strings
 decimal number immediately after the initial @samp{%}, followed by a
 literal dollar sign @samp{$}.  It causes the format specification to
 convert the argument with the given number instead of the next
-argument.  Field numbers start at 1.  A format can contain either
-numbered or unnumbered format specifications but not both, except that
-@samp{%%} can be mixed with numbered specifications.
+argument.  Field numbers start at 1.  A field number should differ
+from the other field numbers in the same format.  A format can contain
+either numbered or unnumbered format specifications but not both,
+except that @samp{%%} can be mixed with numbered specifications.
 
 @example
 (format "%2$s, %3$s, %%, %1$s" "x" "y" "z")
diff --git a/src/editfns.c b/src/editfns.c
index 29af25a..a5088b0 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3901,9 +3901,10 @@ where field is [0-9]+ followed by a literal dollar "$", flags is
 followed by [0-9]+.
 
 If a %-sequence is numbered with a field with positive value N, the
-Nth argument is substituted instead of the next one.  A format can
-contain either numbered or unnumbered %-sequences but not both, except
-that %% can be mixed with numbered %-sequences.
+Nth argument is substituted instead of the next one.  A field number
+should differ from the other field numbers in the same format.  A
+format can contain either numbered or unnumbered %-sequences but not
+both, except that %% can be mixed with numbered %-sequences.
 
 The + flag character inserts a + before any positive number, while a
 space inserts a space before any positive number; these flags only
-- 
2.7.4