Re: [PATCH 6/6] Use Arch instead of Debian for sr.ht builds

Alejandro Colomar via Mutt-dev <[email protected]> Tue, 24 Feb 2026 13:56:20 +0100

Newsgroups	gmane.mail.mutt.devel
Message-ID	<aZ2eOVIjZ8MsAf55@devuan>

Hi Rene,

On 2026-02-24T13:41:26+0100, Rene Kita wrote:
> This explains why it went so smooth with Arch. m-(
> 
> Running the build on Arch I get multiple errors of this kind:
> browser.c:548:17: error: initialization discards 'const' qualifier from
> pointer target type [-Werror=discarded-qualifiers]
>   548 |       char *c = strrchr (d, '/');
>       |                 ^~~~~~~
> 
> This is in function:
> static int examine_directory (MUTTMENU *menu, struct browser_state *state,
> 			      const char *d, const char *prefix).
> 
> AFAIU, strrchr is defined as: char * strrchr(const char *s, int c).

Being Arch, I suspect you're using the latest glibc.  C23 has changed
the prototype of string search functions to use 'QChar', which is just
a way of saying "the const qualifier, if present on the input, is
preserved in the output".
<https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf#subsubsection.7.26.5.6>

This makes it possible to write code that is more type-safe.

Since C23, the standard prototype for strrchr(3) is:

	QChar *strrchr(QChar *s, int c);

which could be documented in a more C++-style way, with overloads:

	char *strrchr(char *s, int c);
	const char *strrchr(const char *s, int c);

I now need to update the manual pages, and think I'm going to use the
latter, although feel free to suggest some preference or some other way
to document it.

The glibc commit that changed this was:

	glibc.git cd748a63ab1a (2025-11-20; "Implement C23 const-preserving standard library macros")

which is contained in glibc-2.43.

> 
> *c is changed later in that function, so we can't make it const. Any
> ideas what's the best way forward from here?

If *c is later changed, and it derives from d, then d must be non-const,
doesn't it?  Or is c later derived from another pointer?  If the latter
is true, then we'd need to use a different local pointer variable.

Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es>

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