Re: [PATCH] Update RE_SYNTAX_EMACS to include features used by GNU Emacs

Updated the comment. Emacs revision in which RE_CHAR_CLASSES is enabled 
is d24873d4, so syntax 0 must have been used for all releases before that

On 4/11/25 22:04, Eric Blake wrote:
> On Fri, Apr 11, 2025 at 04:52:59PM +0300, Vladimir Gorsunov wrote:
>>    When GNU Emacs switched to using gnulib for regular expression
>>    functionality in the etags program, some features stopped working
>>    (please see https://debbugs.gnu.org/cgi/bugreport.cgi?bug=76945 for
>>    details). That is because RE_SYNTAX_EMACS flag combo in gnulib doesn't
>>    have the corresponding flags set. This value should be updated to
>>    fix etags and to better reflect the set of features GNU Emacs is
>>    using at the moment
>>  From 76f937ae2eacb3649117e7f4c05819e82a7c42a9 Mon Sep 17 00:00:00 2001
>> From: vg <[email protected]>
>> Date: Fri, 11 Apr 2025 16:28:29 +0300
>> Subject: [PATCH] Update RE_SYNTAX_EMACS to include features used by GNU Emacs
>>
>> * lib/regex.h: macro update
>> * doc/regex.texi: documentation update
>> ---
>>   doc/regex.texi | 3 ++-
>>   lib/regex.h    | 3 ++-
>>   2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/doc/regex.texi b/doc/regex.texi
>> index cba1e13520..9917a418be 100644
>> --- a/doc/regex.texi
>> +++ b/doc/regex.texi
>> @@ -316,7 +316,8 @@ regular expressions.
>>   The predefined syntaxes---taken directly from @file{regex.h}---are:
>>   
>>   @smallexample
>> -#define RE_SYNTAX_EMACS 0
>> +# define RE_SYNTAX_EMACS						\
>> +  (RE_CHAR_CLASSES | RE_INTERVALS)
> Hmm.  GNU m4 1.4.19 documents that its regex engine matches emacs -
> but that's only because m4 uses syntax 0.  If this change is made in
> gnulib, then either th m4 manual needs to patched to state that it is
> similar to emacs except for lacking character classes and intervals,
> or we make a non-backwards-compatible change in m4 by actually using
> RE_SYNTAX_EMACS instead of 0 for the default syntax.
>
> Since there's already another long thread on how m4 does not match
> current emacs regex but why enabling intervals would break at least
> autoconf 2.72, I'm inclined to update the m4 manual rather than use
> RE_SYNTAX_EMACS, whether or not this patch is accepted.
>
> What's more, this patch is incomplete; if you change RE_SYNTAX_EMACS,
> then you also need to change this paragraph:
>
> /* The following bits are used to determine the regexp syntax we
>     recognize.  The set/not-set meanings are chosen so that Emacs syntax
>     remains the value 0.  The bits are given in alphabetical order, and
>     the definitions shifted by one from the previous bit; thus, when we
>     add or remove a bit, only one other definition need change.  */
>

From 0b7b548c2a547ab84adb0001e7d0629b5b6cb6f8 Mon Sep 17 00:00:00 2001
From: Vladimir Gorsunov <[email protected]>
Date: Sun, 13 Apr 2025 12:18:33 +0300
Subject: [PATCH] Update RE_SYNTAX_EMACS to include features used by GNU Emacs

* lib/regex.h: macro update
* doc/regex.texi: documentation update
---
 doc/regex.texi |  3 ++-
 lib/regex.h    | 12 +++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/doc/regex.texi b/doc/regex.texi
index cba1e13520..9917a418be 100644
--- a/doc/regex.texi
+++ b/doc/regex.texi
@@ -316,7 +316,8 @@ regular expressions.
 The predefined syntaxes---taken directly from @file{regex.h}---are:
 
 @smallexample
-#define RE_SYNTAX_EMACS 0
+# define RE_SYNTAX_EMACS						\
+  (RE_CHAR_CLASSES | RE_INTERVALS)
 
 #define RE_SYNTAX_AWK                                                   \
   (RE_BACKSLASH_ESCAPE_IN_LISTS | RE_DOT_NOT_NULL                       \
diff --git a/lib/regex.h b/lib/regex.h
index 67a3aa70a5..316a8e48fd 100644
--- a/lib/regex.h
+++ b/lib/regex.h
@@ -65,10 +65,11 @@ typedef long int s_reg_t;
 typedef unsigned long int active_reg_t;
 
 /* The following bits are used to determine the regexp syntax we
-   recognize.  The set/not-set meanings are chosen so that Emacs syntax
-   remains the value 0.  The bits are given in alphabetical order, and
-   the definitions shifted by one from the previous bit; thus, when we
-   add or remove a bit, only one other definition need change.  */
+   recognize. The set/not-set meanings are chosen so that the value 0
+   is the syntax used originally by Emacs (pre 21.1, when features
+   started to get added). The bits are given in alphabetical order, and
+   the definitions shifted by one from the previous bit; thus, when
+   we add or remove a bit, only one other definition need change. */
 typedef unsigned long int reg_syntax_t;
 
 #ifdef __USE_GNU
@@ -215,7 +216,8 @@ extern reg_syntax_t re_syntax_options;
    (The [[[ comments delimit what gets put into the Texinfo file, so
    don't delete them!)  */
 /* [[[begin syntaxes]]] */
-# define RE_SYNTAX_EMACS 0
+# define RE_SYNTAX_EMACS						\
+  (RE_CHAR_CLASSES | RE_INTERVALS)
 
 # define RE_SYNTAX_AWK							\
   (RE_BACKSLASH_ESCAPE_IN_LISTS   | RE_DOT_NOT_NULL			\
-- 
2.31.1